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Introduction to fruit crops (Chapter 1 of text)



Man’s relationship with fruiting plants began long before the origins of agriculture in 8000-10,000 BC, when all human beings practiced the hunter-gatherer lifestyle. Fruits gathered from the wild were mainstays of our diet, being excellent sources of fiber, vitamins, and other healthful or medicinal compounds unbeknownst to us then. While cereal grains such as wheat and barley were probably the first crop plants domesticated by humans, several of today’s fruit crops were not far behind since they were native to the very same area – the fertile crescent of Asia Minor. Domestication of wild fruiting plants may have been inadvertent; the first groves of fruit trees probably sprang from seeds thrown in waste heaps at the edge of villages. Careful observation and selection for useful traits such as larger size, better taste, and higher yield started the transformation of those wild plants into the crops we cultivate and enjoy today. During the age of discovery, fruits, seeds or live plants were often taken on transoceanic voyages, and exchanges in both directions helped spread many crops throughout the world. Christopher Columbus and his contemporaries may not have realized the impact they would have on agriculture and society when they brought crops such as coffee and citrus to the new world, and returned to Europe with previously unknown, but now common foods like cocoa and pineapple.

Today, we have well established world trade networks and sophisticated cultural and postharvest technologies that allow fruits to be enjoyed throughout much of the year, instead of mere weeks per year like our ancestors experienced. Global trade has made formerly rare and exotic treats derived from fruit crops commonplace in countries with no hope of cultivating the plants. Fruit crops are important agricultural commodities, adding tens of billions of dollars per year to the global economy, and being major sources of income for developing countries. Worldwide, over 100 million acres of land has been devoted to their production, and the livelihood of literally millions of farming families depends on continued global trade.

This text is designed to acquaint you with the basics of the botany, production, economic value, general culture, and food uses of the world’s major fruit crops. It is formatted as a reference text to allow quick retrieval of essential facts and figures. The following outline is used throughout the text to facilitate information retrieval and keep the discussion as uniform as possible from crop to crop:

  • I. Taxonomy
  • II. Origin, history of cultivation
  • III. Folklore, medicinal properties, non-food usage
  • IV. Production 
  • V. Botanical description
    • Plant
    • Flowers
    • Pollination
    • Fruit
  • VI. General culture:
    • Soils and climate
    • Propagation
    • Rootstocks
    • Planting design, training, pruning
    • Pest problems
  • VII. Harvest, post-harvest handling
  • VIII. Contribution to diet
  • IX. References and further reading

This chapter describes the general concepts and terminology related to each section of the outline. The book assumes only a basic understanding of plant biology and horticulture, and there is a glossary of terms where words underlined in this chapter are defined.

“Fruit Crop” Defined

One would think that the term fruit crop would be clearly defined – not so. In fact, one of the most frequently asked questions from this web site is “…is the tomato a fruit or a vegetable?” My usual reply is “both”, as it is clearly a fruit in the botanical sense, but a vegetable from a culinary perspective. There are also legal definitions on the books, since in some instances vegetables are taxed and fruits are not (or vice-versa). I think it wise to avoid culinary and legal definitions since these change over time and across regions, and the botanical definition of a fruit, being invariable, is a safer bet. I have chosen to define fruit crop as: perennial, edible crop where the economic product is the true botanical fruit or is derived therefrom. The term perennialeliminates crops grown as annuals such as tomato, pepper, melons, and corn, even though the harvested product is the true botanical fruit. Annual cultivation practices differ markedly from those of perennial crops, and to call these fruit crops would only increase the existing confusion. Note that strawberry, an herbaceous perennial, is included in the text despite the fact that in recent decades, much of the acreage is replanted annually. The word edible eliminates perennial crops whose fruits are used for fiber like Kapok (Ceiba pentandra), or strictly industrial oils like tung nuts (Aluerites fordii). The true botanical fruit is the ripened ovary plus any associated parts, and contains the seeds of the plant. While most would not consider coffee and cacao fruit crops, they fit my definition since they’re perennials, and coffee and cocoa are just roasted, ground up seeds of the fruit. African oil palm, coconut and olive might not strike you as fruit crops either, but again, they fit the definition since coconut, olive and palm oils are edible and derived from a true botanical fruit (all drupes). A nut is a dry, indehiscent fruit with a hard shell, and accordingly, several nut crops are included in the text.

TAXONOMY
Plant Names

The scientific or Latin name of a plant is extremely important, as common names vary with location and language spoken. Taxonomic classification places a plant in a large group of related plants (a family), and assigns to it an official name, based largely on Latin and Greek root words. Scientific names generally consist of two italicized words, the first denoting the genus, the second a species within that genus. For example, Malus domestica is the name for the cultivated apple, where Malus is the genus and domestica the species name. In Latin, Malus is a noun meaning apple, or alternatively evil, bad or wrong. [The dual meaning probably stems from the biblical story of Eve and the forbidden fruit in the Garden of Eden]. The species name domestica is an adjective meaning “around the house”, thus the entire name translates roughly to the domesticated apple. Last but not least, someone always has to take credit for things, so the authority is tacked on to the scientific name denoting the person who named the plant. In the case of the apple, it was a botanist named Borkhausen, so the precise, full name for the apple is:textbox

Malus domestica Borkh.

Linneaus, the father of botany, named many plants, which explains the capital letter “L” found at the end of many plant names, such as Pyrus communis L. (pear). The authority is often omitted in popular literature, on nursery tags, or in plant catalogs, so outside of scientific literature it is not often seen. The authority is not italicized, but typically abbreviated, and there are literally thousands of these abbreviations in use today.

To make matters more complex, some plants have been named or renamed several times, so two or more scientific names may be found for the same plant (see sidebar). For example, the Asian pear,Pyrus pyrifolia (Burm. f.) Nak., also is named Pyrus serotina L., so you may see either name used. Yes, this somewhat defeats the purpose of using a unique, scientific name for a given plant, but opinions vary as to which is “right”.

We are all familiar with different types of fruits within a species, such as ‘Red Delicious’, ‘Golden Delicious’, and ‘Granny Smith’ apples. Horticulturists refer to these subspecies as “cultivars“, which means “cultivated varieties”. The term “variety” often is used interchangeably with cultivar, although purists prefer the latter. Note the convention of enclosing the cultivar name in single quotes. The precise name of that green, crisp apple we see in grocery stores is therefore:

Malus domestica Borkh. ‘Granny Smith’, or alternatively written as

Malus domestica Borkh. cv. Granny Smith.

An even finer level of detail is found in some plants, the strain or sport. This is equivalent to a sub-subspecies, or a form, where within a cultivar we have several slight variations that have horticultural importance. An example would be ‘UltraEarli Fuji’ apple, which is a strain of ‘Fuji’ apple that ripens a bit earlier than the original ‘Fuji’. As in this example, strains are often given a new cultivar name if they become commercially important. Another example is ‘Red Max’, a strain of ‘McIntosh’ apple with deeper red color. While this seems like the splitting of hairs, it is useful to note that, in this example, ‘Red Max’ and ‘McIntosh’ are genetically more similar than are ‘Fuji’ and ‘McIntosh’. A few more points will help clarify the use of plant names:

  • After the first reference to a genus in the text, the genus name is often abbreviated using only the first letter. For example, in the chapter on apple, I discuss species related to Malus domestica and refer to these as M. floribunda, M. sargentii, M. micromalus, etc., hoping that you understand that the “M.” stands for “Malus” in each case; this saves valuable typing time for the author and a few drops of ink for publishers.
  • A multiplication sign “X” placed between the genus and species denotes an interspecific hybrid within that genus. An example is the name for the cultivated strawberry, Fragaria X ananassa, which was originally developed by crossing Fragaria chiloensis with Fragaria virginiana.
  • Some genera of plants are so poorly characterized, so diverse, or contain hybrids with complex parentage derived from so many species, that it is convenient to refer to them as a group using the abbreviation “spp.”. Among fruit crops, blackberries are a good example of this, often referred to as Rubus spp.

Figure 1.1 shows an abbreviated family tree for the Rosaceae, or Rose family (one of the most important families of horticultural plants). A family is the major botanical classification group above the genus level, often containing hundreds or thousands of species. Note also the subfamily and subgenus levels, which are useful in pointing out the finer details of genetic relationships among various crops. For example, apple, peach, pear, and plum are all members of the Rose family, but apple is more closely related to pear (both in subfamily Pomoideae) than to peach or plum (Prunoideae). The text lists the family and sometimes the subfamily or subgenus, to give you a sense of the broader genetic background and interrelationships for each crop.

rosaceae

Figure 1.1. Family tree of the Rosaceae, showing the relationships among important fruit crops. The other 3 subfamilies – Spiraeoideae, Chrysobalanoideae, and Neuradoideae – are not shown as they do not contain major crops.

Cultivars

For each crop, I discuss only the major cultivars or groups of cultivars. Even brief descriptions of the many cultivars grown would require a doubling of the length of the text. Cultivars change over time, and vary across different fruit growing regions, making it impossible to cover adequately and keep the text as concise as possible. Several other texts or sources are devoted to cultivar descriptions, including some listed below, and I have included one or two references for each crop that give more detail on cultivars.
Some helpful references on taxonomy in relation to fruit crops:
Bailey et al. 1976. Hortus Third: A concise dictionary of plants cultivated in the United States and Canada. Macmillan Publ., New York.

Borror, D.J. 1960. Dictionary of word roots and combining forms. Mayfield Publ Co., Mountain View, CA.

Downing, C. 1872. Downing’s encyclopaedia of fruits and fruit trees of America: part I and part II. John Wiley & Son, New York.

Facciola, S. 1990. Cornucopia: a source book of edible plants. Kampong Publications, Vista, CA.

Hedrick, U.P. 1922. Cyclopedia of hardy fruits. MacMillan Co., New York.

Lawrence, G.H.M. 1951. Taxonomy of vascular plants. MacMillan Publ. Co., New York.

Moore, J.N. and J.R. Ballington (eds.). 1995. Genetic resources of temperate fruit and nut crops. Acta Horticulturae 290. Vols. 1&2.

Morton, J.F. 1987. Fruits of warm climates. Julia F. Morton, Publ., Miami, FL.

Popenoe, W. 1927. Manual of tropical and subtropical fruits. MacMillan Co., New York.

Samson, J.A. 1986. Tropical Fruits, 2nd edition. Longman Science and Technical, Essex, UK.

Whealy, K. And S. Demuth (eds.). 1993. Fruit, berry, and nut inventory, 2nd edition. Seed Saver Publ., Decorah, Iowa.

Wiersema, J.H. and B. Leon. 1999. World economic plants: a standard reference. CRC Press, Boca Raton, FL.

The national plant germplasm database maintained by the USDA

http://www.ars-grin.gov/npgs/searchgrin.html

ORIGIN, HISTORY OF CULTIVATION
 

The center of diversity of a plant species denotes the area of the world where the species evolved and is found growing in the wild. It is interesting to note that many of the fruit crops (and crop plants in general) grown in the United States are not native to North America. Perhaps more interesting is that several cultivated fruits are not found in the wild, indicating that man has hybridized or selected the species over time to make it very different from its wild progenitors. It is not surprising, therefore, that many of the world’s most common fruits are native to the area where agriculture had its roots – Asia Minor and China.

Knowledge of soil and climatic conditions occurring in the native range give us clues about site selection and cultural methods that should be employed when growing these crops in foreign areas. Also, plant breeders often return to these centers of diversity to collect germplasm useful for disease and pest resistance or other traits. A brief history of cultivation is provided for each crop in the text. Lessons from history have been valuable in shaping the way we grow crops today.
References on crop origins, history:

Diamond, J. 1997. Guns, germs, and steel: the fates of human societies. W.W. Norton & Co., New York.

Evans, L.T. 1998. Feeding the ten billion: plants and population growth. Cambridge University Press, Cambridge, UK.

Upshall, W.H. (ed). 1976. History of fruit growing and handling in the United States and Canada 1860-1972. Regatta City Press, Kelowna, BC, Canada.

 

FOLKLORE, MEDICINAL PROPERTIES, NON-FOOD USAGE
 

Fruits have more than just nutritional value to us; some may contain anti-cancer compounds while others may cause health problems or even death. In this section, I have compiled information from various sources on the folklore, myths, healing properties, and symbolism that has surrounded fruits for centuries. Some of the information on medicinal properties is well-documented, but some of it is speculative. Consult the sources below for more information on medicinal properties of fruits and other plants.
References on folklore, medicinal properties, non-food usage:

Duke, J.A. 2001. CRC handbook of nuts. CRC Press, Boca Raton, FL.

Duke, J.A. and J.L. DuCellier. 1993. CRC handbook of alternative cash crops. CRC Press, Boca Raton, FL.

Lewis and Elvin-Lewis. 1977. Medical Botany: plants affecting man’s health. John Wiley and Sons, NY.

Morton, J.F. 1987. Fruits of warm climates. Julia F. Morton, Publ., Miami, FL.

Ritchason. 1995. The little herb encyclopedia: the handbook of nature’s remedies for A healthier life. Woodland Health Books, Pleasant Grove, UT.

PRODUCTION
 

The production in terms of metric tons (MT) per year (1 metric ton=2200 lb or 1000 kg) or percentage of total is given for the world and the United States. Generally, publication of this data runs about 1-2 years behind the times. In the text, I have used the year 2002 since these data were fairly solid by 2004 when the book was written. Primary sources for this are the Food & Agricultural Organization of the United Nations (FAO), and the USDA Agricultural Statistics Service. In some cases, state agencies or commodity groups have been contacted for these data. Most states in the USA have agricultural statistics services that produce annual reports of agricultural production. Much of this data can now be accessed from the Internet, which is generally more up to date:

FAO - http://apps.fao.org/default.htm

USDA - http://www.usda.gov/nass/pubs/agstats.htm

Table 1.1 The world’s top 20 fruit crops ranked in terms of weight of production per year (FAO 2002).

Crop World Production
(Metric Tons)
Leading country Land Area
(million acres)
1. African oil palm 131,122,544 Maylaysia 27
2. Banana 69,832,378 India 11
3. Orange 64,128,523 Brazil 9
4. Grape 61,018,250 Italy 18
5. Apple 57,094,939 China 12.5
6. Coconut 53,090,561 Phillippines 26
7. Plantain 32,750,510 Uganda 12.5
8. Mango 26,147,900 India 8.5
9. Tangerine 18,792,909 China 4.2
10. Pear 17,115,205 China 3.9
11. Pineapple 14,853,339 Thiland 1.9
12. Olive 15,724,187 Spain 20.5
13. Peach/nectarine 13,815,213 China 3.3
14. Lemon/lime 11,227,173 Mexico 1.9
15. Plum 9,314,727 China 5.4
16. Coffee 7,667,536 Brazil 26
17. Date 6,405,178 Egypt 2.7
18. Papaya 5,950,722 Brazil 0.4
19. Grapefruit/pummelo 4,979,781 USA 0.6
20.  Strawberry 3,237,533 USA 0.5

 

The world’s top 20 fruit crops, ranked in terms of amount of production per year, are given in Table 1.1. I’ve been compiling the top 20 list since 1988, and in my experience, changes are rather minor from year to year. The number 2 spot has rotated among sweet orange, banana, and grape, and other crop rankings move one or two places over time. Keep in mind that FAO statistics are estimates at best, and keeping up with the dozens of fruit crops grown in over 200 countries worldwide is a daunting task. It is worth noting that FAO reports an “NES” category, meaning “not elsewhere specified”, which includes minor fruit crops such as pomegranate, carambola, and guava, as well as some major crops like mango that are misidentified. In all, the NES categories include over 43 million metric tons of fleshy fruits and half a million metric tons of nut crops that collectively would rank #7 in the top 20 list. This statistic is reflective of the great diversity of fruit crops grown around the world. The text covers the top 20, plus the major nuts crops, and a few others of importance native to North America such as blueberry and blackberry.

 

1-1BOTANICAL DESCRIPTION

In the courses I teach, this section is where I spend most of the lecture time. There is a considerable amount of terminology, and it is useful to consult the glossary as you read. The references listed at the end of this section have been invaluable to me, and are highly recommended for further study.

Plant
Most fruit crops are perennial trees, shrubs, or vines. Trees are large woody plants which generally produce a single main stem or trunk, where the renewal growth occurs at the shoot tips in the canopy. The latter is an important distinction between trees and shrubs, since large shrubs can be trained to a single stem, but tend to produce new growth from the base or crown.

Vines or lianas are woody plants that are trained to have a single trunk at the base, but use twining stems or tendrils to support the canopy. Vines rarely have large trunks like trees since they support themselves by climbing on taller plants in nature, or on trellises in cultivation. As a result, vines spend little of their energy on supportive wood, while growing very tall and maximizing leaf exposure to sunlight.

Leaves take many forms, being compound if composed of two or more leaflets, or simple if just a single leaf blade (Figure 1.2). Characterizing the foliage is a great way to start the process of keying out a plant. Several terms are used to describe the overall shape, tip, and margins of leaves or leaflets (Figure 1.3)

Figure 1.2 Compound and simple leaves and their associated parts. The compound leaf shown has a single terminal leaflet, and therefore an uneven number of leaflets. This is termed “odd pinnate”, whereas leaves lacking the single terminal leaflet are “even pinnate”.

1-2 1-3

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Figure 1.3.  Terminology used to describe the overall shapes, tips, and margins of leaves.

Flowers

The floral morphology of a fruit crop is important in determining the mode of pollination (i.e., wind or insect) and type of fruit that will arise when the ovary matures. A complete flower is one possessing all four fundamental appendages: sepals, petals, stamens and pistils. An incomplete flower lacks one or more of these features. The position of the base of the pistil, or ovary, with respect to the other three appendages is important in identification, and also partially determines what the fruit type will be. The two most common positions are inferior (epigynous) and superior (hypogynous). A third possibility is “half-inferior” (perigynous), as found in the stone fruits (Prunus spp.). Figure 1.4 shows that a superior ovary sits above the point of attachment of the sepals, petals, and stamens, whereas the inferior ovary is embedded within the receptacle, below the point of attachment of the other floral organs. A perigynous ovary sits within a hypanthium or floral cup. Different fruit types arise from the flowers shown, partly as a result of the difference in ovary position.

 

inferior superior

Figure 1.4  Superior and inferior ovary position in idealized flowers (above). Below, examples of ovary position in fruit crops: left, a superior ovary in thornless key lime flowers; middle, an inferior ovary of an Asian pear at petal fall; right, a perigynous ovary surrounded by the hypanthium in sweet cherry.

superior ovary thorn- key pear post bloom sweet cherry longi section

A perfect flower possesses both male (stamens) and female (pistil) parts, whereas an imperfect flower may be either staminate (functionally male, having only stamens) or pistillate (functionally female, having only a pistil or pistils). The style is very short or lacking in some pistillate flowers, like in  pecan, but the stigma and ovary are always present if the pistil is functional. If staminate and pistillate flowers are borne on the same plant but in different locations, the species is termed monoecious. If staminate and pistillate flowers occur only on different plants, the species is termed dioecious. One can see the ramifications for pollination and orchard design: a dioecious species such as pistachio or kiwifruit must be planted in an orchard with male plants near females for pollination. Aside from pollination, the male plants are useless since they do not possess ovaries that will ripen into fruit.

An inflorescence is a cluster of flowers, and there are several terms for specific inflorescences (Figure 1.5). Generally, inflorescences fall into two categories, determinate and indeterminate. In a determinate inflorescence, the top-most flower is the most mature, and generally opens first, whereas the top-most flower in an indeterminate inflorescence is the least mature and last to appear. The most common inflorescence types in fruit crops are indeterminate (spikes, racemes, panicles, umbels, corymbs), with the cyme being the most common determinate inflorescence.

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Figure 1.5. Stick figures of different inflorescence types commonly seen in fruit crops. See glossary for complete definitions.

Pollination
Pollination is the transfer of pollen from the anther to the stigma. This is usually mediated by the wind or an insect. In some cases, hummingbirds (wild pineapple), bats (wild bananas), or other animals may play the role of pollinator, but most fruits are pollinated by the familiar honey bee (Apis mellifera).

Once the pollen is transferred, the pollen grain will germinate on the stigma, and the pollen tube will grow downward until it reaches an ovule. This may take a few days. The pollen tube, under control of the tube nucleus, allows for the movement of the two generative nuclei through the style and into the ovule. The processes of pollination and fertilization are depicted in Figure 1.6.

 

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Figure 1.6. Simplified diagram of pollination and fertilization within a typical flower pistil. Some of the details within the embryo sac (exploded view at right) have been omitted for clarity. See text for explanation.

Upon release of the generative nuclei within the embryo sac, the process of double fertilization occurs, involving two fusion events (hence the name, “double fertilization”): one generative nucleus unites with the egg nucleus, and the other generative nucleus unites with two polar nuclei, yielding the zygote and endosperm, respectively. You may want to review the details of double fertilization in one of the references listed below (which will show all of the other details left out for the sake of clarity). Suffice it to say that the end-product of double fertilization is the seed. When a fruit containing seeds is deposited in a suitable place, the seeds germinate, and the life cycle of the plant is completed.

At this point, one might ask: why is pollination necessary for fruit culture, given that seeds are undesirable in fruits from a marketing standpoint? The short answer is that seed development is the prerequisite for fruit set. From the plant’s perspective, a fruit functions in seed dissemination. Therefore, investing a great quantity of photosynthetic energy into a fruit that doesn’t contain viable seed is wasteful. Unpollinated and unfertilized ovaries are therefore dropped from the plant shortly after bloom, as there is no need to invest resources into fruits that cannot aid in the reproductive success of the species. Physiologically, the developing embryos within seeds produce growth regulators that prevent abscission of fruitlets, and cause the fruit tissue in the vicinity of the seed to grow. Thus, dropping of unfertilized ovaries after bloom is “pre-programmed”, and prevented only if there is one or more developing seeds present. In fruits with multiple seeds, poor pollination and low seed set results in misshapen or asymmetrical fruit that are often unmarketable (Figure 1.7).

lopsided apple x-section poor pollin poor achene set & norm

Figure 1.7  A lopsided apple (left) resulting from poor pollination and seed set in only 3 of the 5 locules (center). The right side of the fruit was stimulated to grow more than the left since it was in closer proximity to the developing seeds. On the strawberry (right), the normal fruit at left has uniform achene set across the surface, whereas the fruit at right shows an area of poor set and subsequent underdevelopment.
Having said that, it must have dawned on you by now that there are several types of seedless fruit, and the above argument does not always hold. Fruits that set and mature without seed are termed parthenocarpic, and these species, although rare in nature, have been exploited by horticulturists to a great extent. Examples include Persian lime, some seedless oranges and tangerines, banana, and pineapple. Seedless grapes are perhaps the best known seedless fruits, but are not truly parthenocarpic. They undergo pollination and fertilization, but seed development is aborted shortly afterwards; this situation is termed stenospermocarpy.

Cross-pollination and self-pollination are important terms. Some fruit crops require genetically distinct pollen for fertilization and fruit set to take place, and set fruit poorly if their own pollen is used. These species are planted in orchards with two or morecross-compatible cultivars to favor cross-pollination. On the other hand, some species set more than enough fruit when pollinated by themselves. Such self-pollinating species can be grown in large orchards composed of a single cultivar, which are easier to manage. The cultivar used as a source of compatible pollen is referred to as a pollinizer for cross-pollinating species. Note that transfer of pollen between one flower and another on the same tree is still considered self-pollination, as is the case when pollen is transferred between flowers on separate trees of the same genotype. The key to cross-pollination is having a genetic distinction between the pollen source and recipient.

Many cross-pollinating species exhibit self-incompatibility, such that fertilization by their own pollen is disfavored or prevented through physical or biochemical factors. There are different degrees of self-incompatibility, and many self-incompatible species will produce a few fruit even when self-pollinated. Thus, a single apple tree in your backyard may have a bushel or so of fruit, since apples are not completely self-incompatible, but the same tree may produce several bushels if cross-pollinated. Horticulturists have coined the terms “self-fruitful” and “self-unfruitful” to describe cultivars that can set commercial crops, or cannot set commercial crops (respectively) when self-pollinated. Thus, self-fruitful and self-unfruitful are economic or horticultural terms, whereas “self-incompatible” or “cross-incompatible” are botanical terms.

Highly self-incompatible cultivars or species are often referred to as “self-sterile”, which is technically incorrect. The term “sterile” implies that there is either no viable pollen or no viable eggs to be fertilized. If a cultivar is truly male sterile, for example, its pollen could not fertilize its own or any other egg; the pollen is simply non-functional. Likewise, a female sterile cultivar will not produce viable seed regardless of the pollinizer used. The rabbiteye blueberry (Vaccinium ashei) is a good example of misuse of these terms. When two cultivars of rabbiteye are inter-planted, fruit set is often 50% or more on both cultivars, but if either is planted alone, only about 2% of flowers will set fruit. The latter causes people to think that rabbiteyes are self-sterile. But, since fruit sets on both cultivars when cross-pollination occurs, this indicates that the pollen and eggs of both cultivars are viable (not sterile); rabbiteyes are simply highly self-incompatible.

Fruit
Fruits are matured ovaries plus any associated flower parts, and contain the seeds of the plant. The ovary may be subdivided into two or more carpels (then termed compound ovary) each bearing one to many ovules. Individual carpels develop into sections of a whole fruit, as with citrus where each familiar segment of the fruit represents one matured carpel. If the ovary is not subdivided, then it is termed simple. The ovules will mature into seeds if fertilized.
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The ovary has three layers of tissue: the exocarp (outermost), mesocarp (middle), and endocarp (innermost) (Figure 1.8). These layers may develop into distinct parts of the fruit. Generally, the exocarp becomes the fruit peel or skin, the mesocarp becomes the fruit flesh, and the endocarp becomes the innermost part of the flesh or a specialized tissue surrounding the seed(s), like a pit. In many cases, however, the three layers are indistinguishable, and the term pericarp is applied to denote all ovarian  tissues surrounding the seed(s).

Figure 1.8. Fruits are matured ovaries, and contain the seeds of the plant. Ovaries sometimes have distinct layers of tissues, as labeled above, which develop into distinct structures of the fruit as shown for a drupe. Not all fruits have such clearly demarcated tissues.

 

Fruit types are good identification criteria for plants, and are often determined by floral morphology, particularly ovary position (i.e., superior or inferior). The major fruit types in commercial fruit crops are: pome, drupe, berry, hesperidium, aggregate, accessory, multiple or syncarp, and nut. Use the glossary for descriptions of fruit types, and/or the fruit key below.

Key to Common Fruit Types

1. Fruit developed from two or more separate flowers, or derived from an entire inflorescence
2. Fruit consists mostly of receptacle tissue, with tiny, ripened ovaries borne along the inner wall of the hollow
receptacle………………………………………………………………………………………………………. Syconium (Fig)
2. Fruit consists of tightly clustered ripened ovaries plus
the inflorescence axis…………………………………………………… Multiple or Syncarp (Pineapple, Mulberry)
1. Fruit developed from a single flower
3. Fruit developed from two or more separate ovaries
4. Fruit primarily ovarian tissue; an aggregation fruitlets on a receptacle…………. Aggregate (Brambles)
4. Fruit primarily non-ovarian tissue ……………………………………………………… Accessory (Strawberry)
3. Fruit developed from one ovary
5. Fruit (mostly) fleshy at maturity
6. Fruit with a thin skin, homogenous texture throughout (except seeds) …………….. Berry (Grape)
6. Fruit with heterogenous texture
7. Outer part of fruit tough and hard, or leathery
8. Septa (partitions) present, several to many, rind leathery …… Hesperidium (Citrus)
8. No septa, outer rind tough, thick …………………………………… Pepo (Watermelon)
7. Outer part of fruit soft; thin-skinned
9. Fruit with a hard, bony endocarp surrounding the seed……… Drupe (Peach, Mango)
9. Fruit with two or more seeds, center with papery or cartilaginous
structure surrounding seeds…………………………………………….. Pome (Apple, Pear)
5. Fruit dry at maturity
10. Fruit indehiscent (not splitting open) at maturity
11. Fruit winged …………………………………………………………………….. Samara (Maple, Ash)
11. Fruit not winged
12. Seed fused to fruit wall ………………………………….. Caryopsis, Grain (Corn, Wheat)
12. Seed not fused to fruit wall
13. Fruit wall bladder-like, loose and free from seed………………… Utricle (Spinach)
13. Fruit wall not bladder-like, close-fitting to seed
14. Fruit large, with hard, bony wall ………………………..  Nut (Walnut, Pecan)
14. Fruit small, wall thin  ………………………………………. Achene (Sunflower)
10. Fruit dehiscent (splitting open) at maturity
15. Ovary compound; fruit developed from more than one carpel
16. Fruit splitting into one-seeded segments at maturity, but carpels not
dehiscing to release seeds ……………………………………………… Schizocarp (Carrot)
16. Fruit splitting open to release seeds at maturity
17. Two carpels separated by a thin, translucent septum
18. Fruit less than twice as long as it is wide ……….. Silicle (Shepard’s purse)
18. Fruit more than twice as long as it is wide …………………. Silique (Mustard)
17. More than two carpels, not separated by a thin, translucent septum ….. [Capsule]
19. Capsule opening along a transverse circular line; top separating
like a lid …………………………. Circumscissile capsule or Pyxis (Brazil Nut)
19. Capsule opening lengthwise or by pores, top not separating like a lid
20. Capsule opening by pores or flaps ……….. Poricidal capsule (Poppy)
20. Capsule opening longitudinally, often lengthwise
21. Capsule dehiscing through locules ….. Loculicidal capsule (Iris)
21. Capsule dehiscing through septa …..Septicidal capsule (Yucca)
15. Ovary simple; fruit developed from one carpel
22. Fruit opening along a single suture ………………………………………. Follicle (Milkweed)
22. Fruit opening along two sutures
23. Fruit not constricted between seeds …………………………… Legume (Pea, Bean)
23. Fruit constricted between seeds, sometimes breaking into
one-seed segments ……………………………………………………….. Loment (Desmodium)

The fruit bearing habit of a plant refers to the position and type of wood on which flower buds, and subsequently fruits, occur. This is important in pruning and training, because we want to encourage the type of wood that bears the fruit and minimize unnecessary vegetative growth. Some species are spur bearing, where fruit are borne on very short, slow-growing, lateral branches (Figure 1.9). Spurs develop on 2-year-old and older wood, and may grow only ¼” per year; thus, the fruit are borne at nearly the same points in the canopy from year to year. For spur-bearing species, it is important to keep good light exposure throughout the canopy because shaded spurs fail to form flower buds for next year’s crop. Lateral-bearing species produce fruit from lateral buds on 1-year-old wood. For these species, it is important to stimulate ample growth each year (by dormant pruning, fertilizing, etc) so that enough fruiting shoots are available for the next year. A number of crops bear fruit on current season’s growth, either laterally as in grape, or terminally as in walnut or mango. Some of the tropical crops exhibit cauliflory, where fruit are borne on large branches or trunks of trees (e.g., cacao).

1-11
Figure 1.9. The two most common bearing habits of fruit crops: spur and lateral. Spurs are simply short, lateral branches that occur on 2-year-old and older wood. Apple, pear, and sweet cherry are examples of spur bearing species. Lateral bearing species produce fruit from lateral buds on 1-year-old or current season’s growth, and include peach and grape.

 

 

 

 

Thinning refers to the partial removal of flowers or fruitlets in order to improve the size of the remaining fruit. Thinning is often practiced for large-fruited species that normally set too many fruit. By thinning, one directs the available photosynthate produced by the leaves into fewer, but ultimately larger fruit, rather than many small, unmarketable fruit.

Thinning is accomplished by hand usually, and is obviously very labor intensive and expensive. Flowers or fruits are removed such that a certain number of fruit per tree, or a certain spacing between fruit on a limb is achieved. For example, apples are thinned to 1 fruit per spur, with spurs spaced about 4-6″ apart, resulting in the removal of about 80% of the original number of fruitlets (Figure 1.10). Thinning should be uniform throughout the canopy, as fruit in clusters will remain small even if the correct total number of fruit are left. In some species, chemicals can be sprayed on trees to kill flowers or induce drop of fruitlets. Chemical thinning is less expensive, but riskier since the degree of thinning depends not only on chemical and concentration, but on weather, cultivar, stage of fruit development, and skill of the orchardist.

galabefore thin
galaafterthin

Figure 1.10  Fruit thinning is commonly practiced for large-fruited species, such as apple. In this case, three fruit have been left, one per spur, spaced about 4″ apart. Spacing is important; leaving three fruit on the same spur while removing all others would not yield the same increase in fruit size.

In terms of timing, the earlier the tree is thinned, the better the result. When possible, thinning at bloom provides the greatest improvement in fruit size. However, many growers wait until the threat of frost is passed to thin to make sure there will be enough fruit for a full crop. Much of the benefit of thinning is lost if delayed more than about 45 days post-bloom.

References on plant morphology, flowering and fruiting relating to fruit crops:

Harris and Harris. 1994. Plant identification terminology: An illustrated glossary. Spring lake Publ., Spring Lake, Utah.

Faust, M. 1989. Physiology of temperate zone fruit trees. Jihn Wiley and Sons, New York.

Monselise, S.P. (Ed). 1986. CRC handbook of fruit set and development. CRC Press, Boca Raton, FL.

Nyeki, J. And M. Soltesz (eds). 1996. Floral biology of temperate zone fruit trees and small fruits. Akademiai Kiado, Budapest, Hungary.

Sedgley, M. And A.P. Griffin. 1989. Sexual reproduction of tree crops. Academic press, London.

Soule, J. 1985. Glossary for horticultural crops. John Wiley and Sons, New York.

Westwood, M.N. 1993. Temperate zone pomology, 3rd edition. Timber Press, Portland, OR.

GENERAL CULTURE

For each crop, the main aspects of cultivation can be found in this section. The subsections include: soils and climate, propagation, rootstocks, planting design, training, and pruning, and pest problems.

Soils and Climate
Most fruit crops grow best on deep, well-drained, loamy soils, with pH of 6-7. The rare exceptions to this are noted. Climate is probably the strongest determinant of the success of fruit cultivation. Several aspects of climate are critical.

Cold Hardiness. This is the minimum temperature tolerance for the plant, often quoted in degrees F or C causing 50% or greater mortality. The flower buds, vegetative buds, and wood often have different killing temperatures, with flower buds being the least hardy. Thus, a fruit tree may survive in a northern winter, but produce little or no fruit. Maximum cold hardiness values are given for each species in the text. It is important to note that cold hardiness is not constant; in the summer, most fruit crops would be killed by relatively high temperatures (i.e., 10s or 20s °F or -12 to -2°C). As they acclimate in fall and early winter, they obtain the ability to withstand temperatures well below 0°F (-18°C) in most cases. Conversely, as the buds begin to swell in late winter or spring, several degrees of hardiness are lost per week (Table 2). In almost all fruit crops, open flowers or small fruitlets can withstand only 28 to 30°F (-1 to -2°C) without injury, making most crops vulnerable to relatively mild spring frosts. Fruit growers choose sites less prone to frost, and/or use heaters, sprinkling, or wind machines to prevent crop losses when frost occurs (Figure 1.11). Tropical crops are exceptions – most have no capacity for acclimation and are killed by brief exposure to subfreezing temperatures. Subtropical crops like citrus and date display a modest ability to acclimate and withstand temperatures 5-10°F below the freezing mark.

Table 1.2 Change in killing temperature of apple flowers as they develop during late winter and early spring (modified from Proebsting and Mills, 1978. J. Amer Soc. Hort. Sci. 103:192). Pictures below depict a few of the stages of bud development.

Dormant Silver tip Green tip Half-inch green Tight cluster First pink First Bloom Full Bloom Post Bloom
0F <-4 10 18 22 25 27 28 28 28.5
0C <-20 -12 -7.5 -5.6 -3.9 -2.8 -2.3 -2.2 -1.9

 

dormant spur tight cluster table 1.2center full bloom

 

closeup2

 

 

Figure 1.11. Peach flowers encased in ice during a frost event. Sprinkler irrigation is commonly used to protect fruit crops from frost damage in the temperate zone. The water releases heat as it freezes, keeping flower bud temperatures above the killing point of about 28°F.

Chilling Requirement  – this is the number of hours of exposure to 45°F (7°C) or below required each winter to satisfy dormancy and allow normal growth the following spring. The basic components of dormancy are depicted in Figure 1.12. Most temperate woody plants require between 500-1500 chill hours each winter, measured from leaf drop in autumn until February or March. If the winter is warm, and the chilling requirement is not met, then bud break is sporadic and light, and cropping is poor. If the plant receives much more chilling than needed, bud break is accelerated and often premature, resulting in frost damage. This is why it is important to match the chilling requirement of the plant to the location, and also why temperate species like apples cannot be grown in the tropics where temperatures rarely drop below 60°F. For most species, there are a few low chill cultivars that can be grown in areas with mild winters that would not support growth of traditional cultivars. ‘Flordaprince’ peach and ‘Flordahome’ pear are examples of fruit trees bred specifically for low chilling requirement, and can be grown successfully in Florida, southern Texas, and other warm winter locations. Tropical crops have no chilling requirements, and although they may often flower or break bud after winter in subtropical regions, they do not need the cool exposure to flower or grow normally.

dormancyfig

Figure 1.12. Typical timeline of dormancy in temperate fruit crops (northern hemisphere). Exposure to temperatures below 45°F conditions plants to respond to warm temperatures in late winter and eventually resume growth in spring.

Once the chilling requirement has been satisfied, temperate woody plants must receive a certain number of growing degree hours in order to resume growth. Thus, dormancy can be thought of as a two-stage process: a first stage requiring cool temperature exposure followed by a stage requiring warm temperatures. Some studies suggest that the two stages interact, i.e., a deficit in chilling causes the growing degree hour requirement to increase, and over-chilling reduces the growing degree hour requirement. It follows that bloom date in spring is strongly influenced by winter weather. In areas like the eastern United States, which experience wild fluctuations in winter weather, bloom dates for a given fruit cultivar can vary by 3-4 weeks from year to year.

Growing season length - Some fruit crops require as few as 30 days for fruit maturation, while others require several months or over a year. Species like pecan and kiwifruit require over 200 days between bloom and harvest for proper maturation, hence can only be grown where the growing season is long. The growing season is defined as the time interval between the last frost in spring and first frost in autumn.

Sunlight - Sunlight not only drives photosynthesis, but also drives pigment synthesis in the fruit’s skin, and flower bud formation for next year’s crop. Red color development in apples is much greater in the sunny, desert-like climate of eastern Washington than in the cloudy, humid climate of New York, for example. All fruit crops except coffee and cacao perform best in full sunlight rather than shade.

Rainfall and humidity - Many crops which originated in humid, rainy climates perform well where these conditions are found. When grown in arid areas, irrigation must be provided during the growing season. High humidity and rainfall favor weed, disease and insect outbreaks, and fruits grown in humid regions often require more pesticide applications to achieve the same yield and quality as fruits grown in arid climates. This is particularly true for species native to arid areas that have little natural pest resistance.

Temperature during fruit maturation - The flavor of a fruit is a function of the amounts and ratio of sugars and organic acids found in the pulp. Sugars increase and acids decrease as fruit ripen (Figure 1.13). Warm conditions during ripening favor sugar accumulation and organic acid degradation, rendering the fruit sweeter and richer in flavor. Cooler than desirable temperatures do the opposite – they make the fruit more watery and tart. This is one major reason why there are “vintage” years and poor years for wines. If the weather during late summer/early fall is too cool, then the wine will be acidic, dry, and perhaps low in alcohol, because the grapes never achieved an optimal sugar level and/or sugar:acid ratio. Grape growers hope for sunny, warm days and cool nights during maturation to obtain maximum sugar content and the proper sugar/acid ratio. What is warm weather for grapes may be cool weather for pineapples, so there are no cardinal temperatures applicable to all fruits.
1-13

Figure 1.13. As fruit ripen, they accumulate sugars and lose organic acids as shown above [Modified from Westwood, 1993].

References on climate:

Barfield, B.J. and J.F. Gerber. 1979. Modification of the aerial environment of crops. Amer. Soc. Agric. Engr. Monograph No. 2. St. Joseph, Michigan.

Faust, M. 1989. Physiology of temperate zone fruit trees. John Wiley and Sons, New York.

Schaffer, B. and P.C. Andersen (eds). Handbook of environmental physiology of fruit crops (2 volumes). CRC Press, Boca Raton, Fla.

The National Climate Data Center in Asheville, NC provides detailed weather data on for North America: http://www.ncdc.noaa.gov/oa/ncdc.html

 

Propagation
Most fruit crops are propagated by vegetative means to retain the exact fruit characteristics of the parent plant. Seed propagation generally results in highly variable fruit size, shape, color, and flavor, and creates a management nightmare, since each seedling is genetically different from the others. People recognized this a few thousand years ago and began grafting, budding, or rooting cuttings of desirable fruit crops, rather than planting them by seed. Today, almost all tree fruits are grafted or budded, and most small fruits and some grapes are grown from cuttings. Specialized nurseries produce millions of new plants each year, generally by growing rootstocks for a year, then budding or grafting them with the desired scion cultivars the following year. Many tropical fruit crops are still propagated by seed, including cashew, coffee, oil palm and coconut. They are either fairly true breeding from seed, or cannot be propagated easily by vegetative techniques.The general process of budding or grafting is depicted in Figure 1.14. In this book, I give a brief description of the methods used to propagate a given species, but if you have not studied plant propagation recently or at all, it would behoove you to refer to one of the texts below for general information. Several terms related to propagation are described in the glossary.1-14

Figure 1.14. Basic process of grafting or budding a fruit tree. The rootstock is grown for about one year prior to grafting or budding. Shown here is a seedling rootstock, but some rootstocks themselves are vegetatively propagated. Once the rootstock is of sufficient size, one or more buds from the desired scion cultivar are joined with it via a number of techniques.

 

 

 

 

 

References on propagation:

Garner, R.J. 1988. The grafter’s handbook, 5th edition. Cassell Publ., Ltd, London.

Garner, R.J. and S.A. Chaudhri. 1976. The propagation of tropical fruit trees. Horticultural Review N. 4, CAB International, Farnham Royal, UK.

Hartmann, H.T., D.E. Kester, and F.T. Davies. 1990. Plant Propagation: principles and practices, 5th edition. Prentice Hall Publ., Englewood Cliffs, NJ.

Rom and Carlson (eds). 1987. Rootstocks for fruit crops. Wiley Interscience, New York.

 

Rootstocks

As described above, the rootstock is the root system of a grafted tree. A 2-part tree may be referred to as a “stion”, which derives from stock + scion. The use of grafted trees overcomes many of the problems associated with growing trees from seed, such as:

  • The exact growth, flowering, and fruiting characteristics of the cultivar are preserved through grafting.
  • Juvenility is greatly reduced. Grafted trees begin fruiting at a very early age, often when only 2 or 3 years old. Seedlings of some species may not fruit until they are 5+ years old. Pomologists say that grafted trees are more precocious than seedling trees. Dwarfing rootstocks sometimes induce more precocity than non-dwarfing or seedling rootstocks.
  • Rootstocks allow adaptation of scion cultivars to climates and soils normally unfavorable for growth. Some examples include:
    • Tolerance of poor drainage (e.g., plum rootstocks for peach in wet soils)
    • Tolerance to drought (e.g., Rough Lemon rootstock for sweet orange cultivation on the droughty sands of central Florida)
    • Tolerance of high pH or salinity (e.g., peach x almond hybrid rootstocks for high pH tolerance of peach)
    • Improved cold hardiness and/or bloom delay of scions (e.g., Trifoliate orange rootstock for sweet orange)
    • Tolerance to soil diseases and nematodes (e.g., ‘Nemaguard’ rootstock for root knot nematode resistance in peach)
  • Rootstocks provide tree size control in some species. This is most widely exploited in apple, where there is a range of tree size obtainable by using different dwarfing rootstocks. For example, a ‘Red Delicious’ tree on M.27 rootstock will be only 6 feet tall at maturity, but would be 20+ feet tall if grafted onto an apple seedling rootstock. The availability of dwarfing rootstocks has allowed many innovations in tree fruit culture, such as more efficient planting designs and training systems, reduced pesticide use, and an earlier return on investment for orchardists.

References on rootstocks:

Rom and Carlson (eds). 1987. Rootstocks for fruit crops. Wiley Interscience, New York.

Tukey, H.B. 1964. Dwarfed fruit trees. Cornell Univ Press, Ithaca, NY.

To the Top

Planting Design, Training, Pruning

Planting Design. To achieve high yield and the earliest and highest return on investment, plants must fill their allotted spaces as rapidly as possible, and then be maintained within these spaces through annual training and pruning. Yield of all crops is positively related to the amount of sunlight absorbed by the leaf canopy per acre, so we optimize canopy shape and plant spacing, leaving just enough room between rows to move equipment and labor. The design of an planting should consider this concept primarily, but other factors such as pollinizer placement, row orientation, tree density (number of trees per acre), desired tree height, and training system are also important.

With free-standing trees, we typically see rectangular planting schemes, where the distance between rows is wider than the distance between trees in a row. An orchardist may say that trees are planted 20′ x 15′, meaning that rows of trees are 20′ apart, and trees within the row occur at 15′ intervals. Tree density would be the amount of ft2 per acre (43,560) divided by the space allotted each tree (20*15=300 ft2), giving about 145 trees/acre in this example.
trellis hedgerow
High density orchards contain several hundred to a few thousand trees per acre, and are generally made possible by dwarfing rootstocks (Figure 1.15). In these orchards, individual trees lose their identity as they are trained into continuous fruiting surfaces, looking like long hedgerows. Dwarfing rootstocks keep trees to a manageable height, and induce fruiting at a very early age, generally the 2nd year. Since dwarf rootstocks are poorly anchored, high density orchards are often supported by a trellis of 1-4 wires; the trellis also aids tree training. Vineyards are laid out very similar to high density orchards, using a trellis to support the vines.

Figure 1.15. A high density apple orchard with over 1000 trees per acre.

Training System. The training system refers to the shape of the canopy, which in turn is controlled by pruning and positioning limbs. Again, the main motivation is to maximize light absorption and induce fruiting as soon as possible. There are many training systems for trees, but all stem from 2 basic forms: the central leader and the open center or vase (Figure 1.16). The central leader, and all of its variations, utilize one main central stem (the “leader”) which extends from the trunk to the top of the canopy. At regular intervals along the leader, tiers of scaffold branches are trained to radiate outward from the leader. Each tier of scaffolds extends outward progressively less as you move from the ground up. As shown in the top view, scaffold limbs are not placed directly above another one, as the upper scaffold would shade the lower one. The resulting canopy has a pyramidal or Christmas-tree shape. This allows good light penetration to the lowest scaffolds, keeping them healthy and fruitful. Central leader systems are useful for many species, particularly those with a strong tendency to grow upright like apple, pear, and sweet cherry (Figure 1.17).

1-16Figure 1.16. Stick figures of the two most popular tree training systems. Most other training systems are modifications of these two basic forms.

The open center system, and its variations, have scaffolds originating from a single point on the trunk, and no scaffolds oriented upright or in the middle of the canopy. Generally, about 4 limbs are selected 1-3 ft above the soil which are pointing in different directions (about 90° apart). These limbs are then trained to grow upward and outward, branching repeatedly to fill one quarter of a circular canopy. The canopy acquires a “V” or vase shape as no structural limbs are allowed to grow in the center. This system allows good light penetration to all branches, as light comes in from the sides and through the center of the canopy. It is used for trees which tend to produce rounded, dense canopies with no main leader naturally, like peach, apricot, plum, and almond (Figure 1.17)

central leader apple open center

Figure 1.17. Dead apple and peach trees reveal the basic framework of central leader (left) and open center (right) trees.

Pruning. Annual pruning is necessary for most fruit crops to keep them young, vigorous, and healthy. However, any pruning during the formative years of the plant extends the time it takes to fill its allotted space in the orchard. Thus, pruning is used sparingly when training young plants, but often practiced annually once the plant is mature.

The amount of annual pruning varies tremendously with species. For wine grapes, about 95% of the previous season’s growth is removed every year, but for sweet cherry trees, only interfering branches and water sprouts are removed when necessary. The severity and type of pruning depends on:

•    inherent vigor of the tree
•    anticipated regrowth response
•    fruit size, or the number of fruiting sites needed for a full crop
•    the nature of the fruiting wood; i.e., spurs on 2+ year-old wood, or laterally on 1-year-old stems
•    the training system

If the cultivar is inherently vigorous, it will require more severe pruning to keep it in shape than would a weak-growing cultivar, or one grafted on a dwarfing rootstock. However, severe pruning invites strong, undesirable regrowth. Therefore, while a vigorous plant requires more pruning, it should not be pruned severely enough to stimulate unfruitful regrowth.

In large fruited species like peach, 100 lbs of fruit might be obtained from just a few hundred fruit, since each one weighs 1/4 to ½ pound. But in the small fruited cherry, several thousand fruit may be required to make the same 100 lbs total yield. Thus peach requires far fewer fruiting sites than cherry, and can be pruned more severely without a significant effect on yield.

Recall that some species bear fruit on short, lateral branches called spurs which may produce fruit for several years. Other species produce fruit only on elongated, 1-year-old or current season’s shoots. In spur-bearing species, we want to encourage the spurs to remain fruitful, so light pruning is needed to keep good sunlight exposure, but severe pruning will remove spurs or result in spurs growing out into long, unfruitful shoots. On the other hand, the lateral bearing species need to be pruned at least moderately to encourage formation of new shoots for next year’s crop. This underscores the importance of proper pruning – not only does it affect this year’s crop, but next year’s crop as well.

Some training systems require specialized pruning to maintain tree form. For each crop, the text will give some details on these specific training systems, but here I want to make a more general point on the types of pruning cuts and their effects on regrowth.

There are two basic types of pruning cuts: heading back  and thinning out, or just heading and thinning (not to be confused with fruit thinning). Heading back is when a branch is cut somewhere along its length, leaving some of it behind (Figure 1.18). Thinning out is when a branch is removed at its point of origin, leaving none of it behind. Pruning stimulates regrowth, regardless of the type of cut made, but the location of regrowth varies with the cut. Specifically, heading back causes a localized stimulus at the wound, such that regrowth occurs from buds just below the cut. Thinning out causes a more generalized stimulus throughout the tree canopy, and does not stimulate regrowth at the cut.

1-17

Figure 1.18. The two basic types of pruning cuts and associated regrowth response.

1-18
Orchardists use heading cuts to induce branching at a specific point; say, where a tier of scaffolds should be positioned in a young, central leader tree. They use thinning cuts where the canopy is too thick, or a branch is growing in the wrong orientation. Thinning misguided branches removes a problem, and sends a stimulus to the remaining, properly oriented branches. Figure 1.19 shows how heading and thinning cuts are used to train a young tree to a central leader system. Also shown in this figure is the proper time for pruning: late winter. Sometimes pruning is done in the summer to eliminate excess growth and improve light penetration into the canopy. Pruning in the autumn should be avoided since it can reduce cold hardiness.

Figure 1.19. Training of a single-stemmed, young tree to a central leader in 2 years with heading and thinning cuts.

References on planting design, training, and pruning:

Baugher, T.A., and S. Singh (eds). 2003. Concise encyclopedia of temperate tree fruit. Haworth Press, New York.

Childers, N.F., J.R. Morris, and G. S. Sibbett. 1995. Modern Fruit Science, 10th edition. Norman F. Childers, Publ, Gainesville, FL.

Galletta, G.J. and D.G. Himelrick (eds). 1990. Small fruit crop management. Prentice-Hall, Eglewood Cliffs, NJ.

Gilman, E.F. 1997. An illustrated guide to pruning. Delmar Publ., Albany, NY.

Jackson, D.I. 1986. Temperate and subtropical fruit production. Butterworths of New Zealand, Wellington, NZ.

Ryugo, K. 1988. Fruit culture. John Wiley and Sons, New York.

Teskey, B.J.E. and J.S. Shoemaker. 1978. Tree fruit production, 3rd edition. AVI Publ., Westport, Conn.

Westwood, M.N. 1993. Temperate zone pomology, 3rd edition. Timber Press, Portland, OR.

A note about backyard fruit growing. Some of the cultural practices detailed in this text may not be appropriate to backyard fruit culture. If you live in an area that happens to be one of the main production centers for a crop, then you’re fairly safe in adapting the commercial practices to your own backyard. It stands to reason that I can offer only generalized advice, which may or may not be sufficient for you to be successful. In most areas of the world, particularly North America, information provided through government extension services is available, generally free of charge on the Internet, or from the local Extension Agent or Farm Advisor. Below I’ve listed key Land Grant universities that publish this type of information and the web addresses as of 2004.

 
Region Land Grant Universities Website
Northeast Cornell
Penn State
http://www.hort.cornell.edu/

http://tfpg.cas.psu.edu/

http://ssfruit.cas.psu.edu/

Mid Atlantic Virginia Tech
North Carolina State
Region-wide
http://www.ento.vt.edu/Fruitfiles/VAFS.html

http://www.ces.ncsu.edu/depts/hort/hil/hfruitnew.html

http://www.caf.wvu.edu/kearneysville/fruitloop.html

Southeast Univ of Georgia
Univ of Florida
http://www.uga.edu/hort

http://edis.ifas.ufl.edu/DEPARTMENT_HORTICULTURAL_SCIENCES

Midwest Michigan State http://www.msue.msu.edu/fruit/
Inter-mountain west Colorado State http://hla.agsci.colostate.edu/
Southwest Texas A&M http://aggie-horticulture.tamu.edu/extension/fruit.html
Pacific Northwest Washington State
Oregon State
http://treefruit.yakima.wsu.edu/

http://oregonstate.edu/dept/hort/

California Univ. of California – Davis http://fruitsandnuts.ucdavis.edu/

Pest Problems
For each crop, the major problems that occur in many regions or the largest production region are highlighted. This section must be generalized because pests and diseases tend to be highly regional. Once again, refer to the sources listed above for specifics on pest management. Here, I present a brief overview of major pests of fruit crops and their management options.

Weeds
Although “weed” doesn’t fit some people’s definition of pest, the single greatest limitation to yield in agriculture is weeds, and more herbicides are used in the USA than all insecticides and fungicides combined. Fruit crops are intolerant of heavy weed infestations or turf grass growing next to the trunk (Figure 1.20). Three basic control strategies for weeds are herbicides, mulches, and cultivation. Commercially, growers generally keep a weed-free strip beneath trees using herbicides or mulch (Figure 1.21). Mulching is effective, but more labor intensive and costly than herbicides. Organic growers frequently use mulches since herbicides are not cleared for use in organic orchards. Cultivation is used often in arid climates in conjunction with flood irrigation, or with crops harvested from the ground (nuts). Cultivation can damage roots and tree trunks, and increase erosion. In developing countries, or on small organic farms growers may weed plots with hand implements. In this text, nothing more will be said about weeds of individual crops, and it can be assumed that weeds are problems in the production of all fruit crops.

apple is k-31 sod apple herb strip

Figure 1.20. Three-year-old ‘Empire’ apple trees with different amounts of weed competition. At left, tall fescue grass was allowed to grow up to the trunk; at right, tall fescue was kept at least 4 ft away on all sides (photos courtesy of Mike Parker, NC State Univ.).

herb strip n ga apples
f20prun6
organic apple orchard

Figure 1.21. Orchard floor management with herbicide strips beneath trees and grass row middles in apple (above), clean cultivation in grapes (center), and mulch strips in an organic apple orchard (below).

Insects and Mites
There are literally hundreds of thousands of species of insects – more than any other life form on the planet. In some fruit crops, up to 300 insects have been documented to cause damage to one or more parts of the plant. Fruits are particularly attractive to some insects since they are sources of food and protection, and useful sites for raising the next generation (Figure 1.22). Generally, only a few cause economic injury to any given crop, and often one or two represent the bulk of the outlay for insecticides or other forms of protection. The text focuses on these key pests, as a complete discourse on all species affecting the crop is prohibitively lengthy. Some of the most common insect and mite problems of fruit crops are listed in Table 1.3.

ofm feeding on seed

Figure 1.22. Larvae of the oriental fruit moth feeding on the seed of a developing peach fruit. Infestation this early generally causes fruit drop.

Table 1.3. Major insect and mite pests affecting fruit crops.

Insect Crops affected1 Damage
Codling moth
(Cydia pomonella)
Apple, pear, plum, walnut Fruit feeding, fruit drop
Oriental fruit moth
(Grapholita molesta)
Peach, plum, apricot, almond, apple Shoot dieback, fruit feeding, fruit drop
Plum curculio
(Conotrachelus nenupar)
Peach, plum, apple, cherry, blueberry Surface scarring, catfacing, fruit feeding, fruit drop
Leafrollers (e.g., Platynoda, Argyrotaenia spp) Apple, pear, peach, plum, grape, citrus, strawberry Leaf & bud feeding, damage; webbing on fruit; fruit damage and subsequent rot
Scales (e.g., Quadraspidiotus) Most fruit crops Fruit scarring, cosmetic damage; leaf feeding; limb and twig dieback, tree decline; honeydew secretion and sooty mold development
Stink bugs & Plant bugs (e.g., Leptoglossus, Lygus) Most fruit crops Fruit catfacing, spotting
Aphids (e.g., Aphis) Most fruit crops Leaf and shoot feeding, distortion; honeydew secretion and sooty mold development; virus transmission
Leafminers (e.g., Lithocolletis) Citrus, apple Leaf feeding by tunneling
Mites (e.g. Tetranychus, Panonychus) Most fruit crops Leaf feeding, stippling, distortion; webbing at shoot tips

1Partial list of major crops affected
mite stipple keraji
Mites are spider relatives, not true insects, which injure plant tissues by puncturing cells on the surface and ingesting the contents. Feeding damage results in a stippled appearance of leaves and other organs attacked (Figure 1.23). If unchecked, leaves lose the ability to photosynthesize efficiently, and often fall off prematurely. Fruit feeding may cause undesirable blemishing or stippling of the peel, causing a downgrade in fruit external quality.

Figure 1.23. A normal mandarin leaf (left) and one damaged by mite feeding (right) showing the familiar stipple symptoms.

Plant Diseases: Fungi, Bacteria, Mycoplasmas, and Viruses
Fungi cause most diseases of fruit crops. The fungi are a highly diverse and widespread group of organisms, ranging from simple water molds and mildew to beneficial organisms like yeast and mushrooms. Their life cycles are extremely complex, but all produce spores of some type that float on wind currents, splash around on raindrops, or hitch rides on insects. Once the spore reaches a suitable host, it germinates and the fungus grows through or on the tissue, provided ample water is available. That’s the critical issue in many cases – the presence of water – and the reason that crops grown in dry climates often have far less fungal disease than those grown in humid climates. Fungal diseases can affect any part of the plant, and those affecting fruit directly are some of the worst problems facing fruit growers (Figure 1.24). Common diseases of fruit crops are listed in Table 1.4.

peach brown rot 24.9 left

Figure 1.24. The brown rot fungus on ripe peaches (left). The tan dots are spore masses. Note the spread of the fungus between two adjacent fruit. The bacterial disease fire blight on a pear shoot (right). Dying shoots turn black and exhibit a typical “shepherd’s crook” shape.

Table 1.4 Major fungal and bacterial diseases of fruit crops.

Disease Crops Affected Symptoms and Damage
Fungal diseases – leaves and stems
Powdery mildew (Podosphaera, Sphaerotheca, and Uncinula spp) Apple, grape, strawberry, cherry, peach, plum Distorted, stunted growth at shoot tips with white, powdery spore masses on both sides of leaves; web-like russeting or discoloration of fruit
Leaf spots or scabs (e.g., Mycospharella, Venturia) Apple, pear, peach, strawberry, many others Circular, angular or irregular blemishes or lesions on leaves. Spots often coalesce to form blotches if severe.
Fungal diseases – fruit
Brown rot (Monilinia spp) Peach, apricot, plum, cherries, almond, quince The blossom blight phase kills flowers at bloom; the fruit rot phase occurs within days of harvest. Brown, soft spots spread rapidly, producing powdery tan spores.
Gray mold or bunch rot (Botrytis spp) Grape, strawberry Classic grey, velvety covering over ripe fruit; fruit softens, shrinks as a result.
Anthracnose (Colletotrichum spp.) Banana, mango,  avocado, papaya, pineapple Small to large, brown or black, sunken lesions on fruit surface near harvest; lesions may coalesce in badly infected fruit. Lesions usually dry and firm.
Fungal diseases – trunk, crown, and roots
Armillaria or oak root rot (e.g., Armillaria) Apple, grape, peach, plum, cherry, apricot, walnut, citrus, many others Wilting, decline, and/or dieback of the aboveground portion of the tree; a conspicuous white mycelial mat forms between the wood and bark of affected trees, and clusters of mushrooms may grow at the base of the trunk
Stem canker (e.g., Leucostoma, Phomopsis) Apple, pear, peach, plum, cherry, apricot, almond, many others Sunken, discolored, or rough areas in bark; often round or elliptical in shape. Size variable, may grow in size from year to year. Limb weakening or dieback through girdling. Callus tissue may form at margins of large cankers.
Vascular wilt (e.g., Verticillium, Fusarium) Peach, plum, apricot, cherry, black- and raspberries, almond, strawberry Leaves wilt, become chlorotic or turn brown, followed by shoot dieback. Often one limb or side of the plant affected before other(s). Yellow, red, or brown discoloration of vascular tissue.
Phytophthora root/crown rot Apple, pear, peach, apricot, cherry, plum, citrus, others Poor shoot growth, chlorotic leaves and generally lack of vigor. Shoot dieback and tree collapse may occur after rainy periods.
Bacterial diseases
Bacterial canker (Pseudomonas syringae) Peach, plum, apricot, cherry, almond, walnut, others Irregular, sunken areas in bark; variable in size. Often with amber gum exuding from canker in spring. Tissue beneath cankers is discolored and often sour smelling. Twigs, limbs, or entire trees dieback, but tree sprouts from rootstock since roots are alive.
Crown gall (Agrobacterium tumefaciens) Over 200 species of woody plants Galls or tumors from ¼” to 6: in size form at the crown or on main roots. Tree may not exhibit foliar symptoms if galls are small; large galls may cause stunting and leaf chlorosis, particularly on young trees.
Fire blight (Erwinia amylovora) Pear, apple, quince Browning or blackening and withering of flower clusters or current season’s shoots. Shoots appear burned, and curl at tips into a “shepherd’s crook” shape. Entire limbs and trees can be killed by girdling
Leaf scorch, scalds, declines (Xylella fastidiosa) Peach, plum, grape, citrus; species in over 30 plant families This is a bacteria-like organism called a mycoplasma; it grows in the xylem and restricts water and nutrient flow, often for years before the tree or vine succumbs.

Bacterial diseases of fruit crops are not as common or diverse as fungal diseases, but more difficult to control. In fact, the only solution for some crops is to produce them in areas where bacterial growth and dissemination is disfavored. For example, pears were cultivated commercially in New York, Pennsylvania, Michigan, and other eastern states in the 1800′s and early 1900s. The bacterial disease Fire Blight (Figure 1.24) wreaked havoc in these rainy, humid climates, and pear culture gradually moved to the arid Pacific Northwest where the disease does not develop as well. As in humans, bacterial diseases can be treated with antibiotics, but this is cost prohibitive for most commercial fruit growers. Quite often, the only solutions are to grow resistant cultivars, or to remove and destroy infected plant parts as soon as the infection is noticed.

Mycoplasmas are somewhere between bacteria and viruses on the evolutionary scale of life. Diseases such as Pierce’s disease of grape, plum leaf scald, and phony peach are examples of the blight that mycoplasmas bring to the fruit world. Mycoplasmas colonize the water-conducting tissues of woody plants, and after multiplying for months or years, they eventually clog the xylem and kill or severely debilitate the plant. Insects that feed on xylem sap, such as leaf hoppers and spittle bugs carry them from plant to plant. It is not feasible to control the disease through insecticide spraying, because it takes only one feeding event from one insect to transmit the disease. Injections of antibiotics can slow the disease, but resistant cultivars, rouging, and quarantines are the only practical methods of control.

Viral diseases are similar to mycoplasmas in many respects. They are moved by insects in many cases. They may also move on pruning tools and some even in pollen, so are a bit more mobile than the mycoplasmas. Once a plant is infected, it remains so for the rest of its life. As in human medicine, there is no cure for viral diseases. Viruses usually cause striking symptoms like mosaic yellowing of leaves, unusual spotting patterns, or twisting and contortion of leaves and shoots, so it is easy to spot an infected plant and remove it from the site. Plants can live many years after being infected with a virus, sometimes without showing obvious symptoms, and thus be a source of infection for other trees for long periods of time. Rouging infected plants is often the only means of controlling viruses.

Nematodes
Nematodes are microscopic, non-segmented round worms that feed on roots of plants. Nematodes are one of the most diverse groups of organisms on the planet, with hundreds of thousands of species named (and still counting). Species in only 2 of 15 orders of nematodes actually parasitize plants, but that leaves more than enough to go around. Virtually every agricultural crop known to man plays host to a dozen or so nematodes. The most common fruit pests tend to be in the root knot (Meloidogyne), ring (Criconemella), dagger (Xiphinema), root lesion (Pratylenchus), and cyst (Heterodera) groups. Despite their diversity, nematodes cause similar injury symptoms because they simply feed on roots, reducing the ability of the root system to support the top of the plant. Stunting, wilting, chlorosis, and in severe cases, toppling over are common symptoms. While they cannot be seen with the naked eye, the result of their feeding is often easily detected in the form of root galls, knots, lesions, or simply poor root development (Figure 1.25).

banana root nema banana toppled

Figure 1.25. “Banana topple” disease, caused by Radopholus nematode feeding on roots (left). Root death leaves plants poorly anchored, and they fall over easily in heavy rain or wind (right).

Soil fumigation prior to planting is often recommended in soils with high nematode populations. Fumigants and other nematicides are highly toxic chemicals that provide good control, but are dangerous to work with and strictly regulated by federal, state and local government agencies. Methyl bromide, the chief soil fumigant used in fruit crops, has been gradually phased out of production due to its ability to escape into the atmosphere and cause ozone depletion. Alternatively, tolerant rootstocks can be used for certain crops; for example ‘Nemaguard’ rootstock for peach, which resists root knot nematode feeding (Meloidogyne incognita). Note that nematode resistant rootstocks resist feeding by only a few species of nematodes at best, and no rootstock resists feeding by all nematodes.

Basic approaches to pest control
Pesticides are not the only way to deal with pests. They are extremely effective and commonplace today, but agriculture was practiced for several thousand years before the development of synthetic pesticides. I divide approaches to pest control into five basic strategies, recognizing that elements of 2 or more strategies may be utilized by a given fruit grower.

Let nature take its course. Doing nothing is easy, so letting nature take its course is quite popular with backyard gardeners. In fact, there is solid scientific justification for doing nothing, since every native pest has some natural enemy, and sooner or later that enemy will bring the pest population back into balance, at least from Mother Nature’s viewpoint. The real question is whether that natural balance occurs at a point where a commercial grower can make a profit. A commercial grower with the thinnest of profit margins can scarcely afford to throw out even one tenth of their crop. This method is also used in integrated pest management (IPM, see below) when pest pressures are not severe enough to warrant action. The direct environmental impact of this method is obviously none, but indirectly, if more land must be cleared for cultivation to compensate for lower yields, the impact of doing nothing can be severe.

Cultural Control. This includes all non-chemical or biological means to control pests. Generally, these are not as rapidly effective as chemicals and done well in advance of pest outbreaks. An example would be closely mowing the grass beneath orchard trees to remove stink bugs living there, just waiting to jump on the newly set fruit after bloom. Cultural controls help to relieve or reduce pest pressures, and often reduce the number of chemical sprays required, but alone they infrequently reduce pests to insignificant levels. The environmental impact is generally minimal, but some cultural controls can damage the environment; for example, tilling weeds and leaving the soil exposed may accelerate erosion. Here are some important cultural controls in brief:

  • Sanitation – One bad apple can indeed spoil the whole bunch, so locating and rouging out the bad ones, when feasible, is a good idea. A flower, fruit, leaf or twig affected by a pest is often the source for further infection within the same tree or orchard. With sanitation, one is physically removing the pest organism and/or its means of propagating itself, which slows the rate of pest build up. One example is pruning out fire blight affected shoots in pears and apples to remove the bacteria that could otherwise affect another shoot within the tree. Disease organisms often overwinter in trees they affected the previous summer, so dormant pruning presents an opportunity to reduce the pest’s potential numbers in the upcoming season.
  • Life cycle disruption – If one can disrupt any point of a pest’s life cycle, its population will collapse. For insects, this has been exploited commercially with the use of pheromone mating disruption. Pheromones are chemicals that allow insects to communicate, and certain pheromones allow male insects to find females during the mating period. Once the specific mating pheromones were identified, researchers reasoned that saturating an area with pheromone would prevent males from finding females. Commercially, this is done for pests such as grape berry moth and codling moth by attaching plastic ties to tree limbs that release pheromone. This works great for large orchards, or in any case where the mating takes place in the orchard. In small, irregularly shaped plantings, there’s a lot of border area, and adults can easily mate outside the orchard, after which the female can fly in to lay eggs. Nevertheless, this has reduced the need for chemical sprays for certain pests substantially, and is a strategy with almost no non-target effects.
  • Traps, baits, diversions – Similar to the foolery involved in life cycle disruption, we can use pheromones or other attractants to lure insects to traps or diversions and kill them, or at least steer them away from the crop. The insect is often lured by visual or chemical cues to a sticky trap where it lands and cannot escape. This has been very successful for controlling flies that produce maggots in apple, blueberry, and cherry. For apple maggot, decoys are made that look like nice red fruit for laying eggs (Figure 1.26). The decoys are laced with insecticide, killing all flies that approach. They are also made of cornstarch so they break down naturally in the field. In some trials, pesticide application has been reduced by 90% using this method.
  • Resistant cultivars – This is the ultimate in cultural pest control strategies, simply planting cultivars that are genetically resistant to the pest. Sounds easy, and has worked in the past for some key pests, but resistant cultivars are slow to develop and sometimes unavailable. Also, pest resistance is specific; years of breeding may go into conferring tolerance to one species (or subspecies) of a pest, leaving several others available to affect the crop. Last, the pest often breaks down the resistance of the host if the two are left alone in the evolutionary landscape for a period of time, which makes breeding an ongoing effort.

 

apple maggot decoys apple maggot decoys2

Figure 1.26. Fruit decoys for control of apple maggot. At left, USDA entomologist Michael McGuire examines decoys in an apple tree. At right, Erica Bailey prepares a cornstarch based apple decoy. The red color attracts the flies to the decoy for egg laying, and the insecticide within kills the adult.

Biological Control. This involves introducing other organisms that prey on or parasitize the pest of the fruit crop. Biological control is extremely effective for specific pest problems, but has yet to achieve the widespread use of most other pest control strategies. For example, introduction of the Vedalia beetle to control cottony cushion scale in California citrus eliminated the need to spray for that pest. Since other insects may attack citrus, unfortunately, Vedalia beetles are killed while spraying to control something other than cottony cushion scale. Another limitation is the need for at least some pest population to be present to support the biological control agent. This basal pest population may be above the threshold for economic loss. Also, the bio-control agent may need other sources of food besides the pest to live, and we may not have these present or even know what they are in some cases.

Chemical Control.  Pesticides are much more responsive than cultural or biological controls, allowing a grower to react instantly to a crisis, and quickly reduce pest populations. Unfortunately, many non-target organisms are affected by chemical applications, and there is potential for human and environmental damage from pesticide misuse. Chemicals have evolved over the years to be less persistent in the environment and have fewer non-target effects, and some of the worst chemicals (e.g., DDT and EDB) were banned years ago. In some cases, availability of pesticides prompted growers to reduce cultural controls in favor of spraying chemicals every few weeks (days) to control pests without knowing whether or not they were present. This spray-by-calendar strategy is not common anymore due to the advent of integrated pest management.

Integrated Pest Management (IPM). As the name suggests, many methods of control are used in an integrated fashion to reduce crop losses. Cultural and biological controls are often used, and pesticides are applied only when other means fail to keep pests below a certain threshold. This threshold, determined by years of research, is the level of pest infestation that can be tolerated before economic losses occur. IPM generally reduces the effect of pesticides on the environment by reducing the number of spray applications, not eliminating sprays entirely.

Scouting is used in IPM to determine if thresholds have been reached. For example, a scout might sample 50 leaves in an orchard block, and count the number of mites on the underside of each leaf. If an average of more than 2 mites per leaf were found, the grower would take action and spray, since research shows that the 2 mites per leaf threshold is the point where economic losses begin to occur. Pheromone traps are often used in IPM to monitor pest populations (Figure 1.27). Unlike the apple maggot traps described above, they are not designed to control the insect population, but serve as indicators of pest presence and aid the grower in spray timing.

insect trap

Figure 1.27. Entomologist Dan Horton places a pheromone trap in an apple tree to monitor insect populations and advise growers on spray timing.

IPM demands greater technical knowledge – growers must be able to recognize all types of insects, fungal signs and symptoms, etc, and quantify their extent quickly. Alternatively, consultants or scouts are available for hire to do this work, or an extension agent may be assigned the task in commercially important fruit-producing regions.

Organic farming has received great attention over the last decade or so, and is currently the fastest growing segment of agriculture in the United States. Pest management in organic farming is really just a form of IPM that does not use synthetic chemicals as a control option. One common misconception is that “organic” means “not sprayed with chemicals”. A certified organic farmer can use chemicals for pest control if they are naturally occurring or plant-derived. This does not mean that such chemicals are not toxic to humans or wildlife. For example, rotenone, a natural insecticide compound, is extremely toxic to fish and can be harmful to pesticide applicators. In some cases, such as apples in humid climates, organic farmers spray pesticides more frequently and apply far more active ingredient per acre per year than conventional farmers. Organic fruit growers can afford higher crop losses because current prices are often double those paid for conventional produce. The upsurge in organic farming has prompted all fruit growers to rethink their approach to pest control and pesticide use.

Food safety in fruit crops. In the United States, the Food and Drug Administration (FDA) has the responsibility of enforcement of the Environmental Protection Agency (EPA) standards in the nation’s food supply. They routinely test food destined for the consumer’s kitchen for a variety of chemical and biological hazards. There are also state agencies that do essentially the same thing, adding another layer of safety assurance. Figure 1.28 shows an example of residue testing by the FDA in 2001. The domestic data is derived from fruit samples collected from 41 states and Puerto Rico. The 2001 data are typical for domestic fruit, showing about 1% violative samples. A violative sample is one containing even a trace amount of a pesticide not registered for that crop, or an amount of legally registered pesticide above the crop tolerance. Crop tolerances are set by the EPA at levels at least 100-fold below the level that caused no observable effects in lab animals that ate the pesticide every day of their lives. Imported fruit data is derived from fruit samples from 99 countries with Mexico the primary source. Imported fruit contained slightly more violative samples in 2001, but also had a higher percentage of no detectable residues. Thus, 97-99% of the time, fruit consumed in the United States has either no residue or residues that fall well below EPA tolerance.

domestic fruit residues
imported fruit residues

Figure 1.28. Pesticide residue test results from 2001 by the Food and Drug Administration for domestic fruit (above) and imported fruit (below).

References on pests and pest control:

Print Resources:

Alford, D.V. 1984. A colour atlas of fruit pests. Wolfe Publ., London.

Avery, D.T. 1995. Saving the planet with pesticides and plastic. Hudson Institute, Indianapolis IN.

Croft, B.A. and S.C. Hoyt. 1983. Integrated management of insect pests of pome and stone fruits. John Wiley & Sons, NY.

Flint, M.L. 1998. Pests of the garden and small farm: a grower’s guide to using less pesticide. Second edition. Univ. Calif. Div. Agric. & Nat. Res. Pub. 3332. 276 pages.

Lind, K., G. Lafer, K. Schloffer, G. Innerhofer, and H. Meister. 2003. Organic fruit growing. CABI Publ., Wallingford, UK.

Ogawa, J.M. and H. English. 1991. Diseases of temperate zone tree fruit and nut crops. Univ. Calif. Div. Agric. & Nat. Res. Publ 3345. 461 pages.

Pena, J.E., J.L. Sharp, and M. Wyoski. 2002. Tropical fruit pests and pollinators. CABI, Wallingford, UK.

Ploetz, R.C. (Ed). 2003. Diseases of tropical fruit crops. CABI, Wallingford, UK.

The American Phytopathological Society has published a series of Compendia on crop diseases including apple and pear, blueberry and cranberry, citrus, grape, raspberry and blackberry, stone fruit (peach, plum, apricot, cherry), strawberry, and tropical fruit (Banana, coconut, mango, pineapple, papaya, avocado). Full citations of compendia are given at the end of the relevant crop chapters.

Web Resources:

On the issues of pesticides and food safety, Extoxnet: http://ace.orst.edu/info/extoxnet/ is a collaborative effort among extension specialists from several universities. The information is unbiased and science-based.

The USDA site on organic food production: http://www.nal.usda.gov/afsic/ofp/

Photos of insects and diseases of many crop plants: http://www.insectimages.org/ and http://www.ipmimages.org/

The EPA’s page on pesticides: http://www.epa.gov/pesticides/

The actual data from the FDA’s Total Diet Study, which monitors pesticide levels in food in the USA: http://www.cfsan.fda.gov/~comm/tds-toc.html

HARVEST, POSTHARVEST HANDLING

Harvesting is usually the most labor intensive, expensive component of fruit growing, as it is usually accomplished by hand. Also, many workers are needed to sort, grade, and pack the harvested fruit. In this section, I present the basics of harvesting and handling common to most species.

As the fruit reach maturity, one must decide when to harvest. Harvesting too early results in poor size and quality, and harvesting too late causes many of the fruit to soften, bruise, or rot before reaching the consumer. Experience is key in this decision, but there are a few tools that commercial growers can use to objectively determine harvest date. Two of the most common tools are the refractometer, which measures the sugar content, and the firmness meter (or penetrometer), which quantifies the firmness of the flesh (Figure 1.29). As a fruit matures, sugars accumulate and the flesh softens. From research, or past experience, growers know the ranges of sugar content and firmness that correspond to a given cultivar and its intended market. For example, apples intended to be stored for long periods are picked more firm than apples intended to be marketed immediately.

refr&pressure

Figure 1.29. A refractometer for measuring “soluble solids” or basically sugar content of fruit juice (left). The penetrometer or firmness meter (right) measures the force required to crush the flesh. Both are rapid field methods for monitoring crop development and determining when to harvest.

Fruit color is also important in determining maturity, and strongly influences consumer acceptance. However, color may develop in the fruit skin well before or after the pulp reaches the optimal sugar content or firmness, so skin color should not be relied upon exclusively. The background color (or ground color) of the fruit is often better correlated with pulp characteristics than the red or highlight color.

Other methods have been developed for specific crops. In fruits that store starch and gradually break this down into sugars, a starch test can be performed to assess how much breakdown has occurred. In cherry, the “fruit removal force”, which is the tension required to pull the fruit off, is measured with a pull gauge. Fruit used for processing into juice or wine undergo more sophisticated measurements of sugar content, acid content, pH, sugar/acid ratio, and other chemical constituents before they are harvested.

As mentioned above, hand harvest is the norm, but in several crops mechanical harvesters have been developed. These devices shake, slap, or vibrate the plant to dislodge the fruit, and then collect the fruit as it falls. Mechanical harvesters are most frequently used for nut crops and fruits intended for processing, since blemishes or bruises are unimportant or do not occur in these crops.

Fresh fruit are washed, graded, sorted, and packaged postharvest (Figure 1.30). Most fruit are graded by size, and less often by color. They are packed in various containers: mesh and plastic bags, cardboard boxes, single-layer flats, and plastic “clamshells” for berries. Perishable fruits are generally shipped immediately after harvest and packing, but long-keeping fruits like apple and some pears may be stored for months prior to packing and shipping.

washing bunches

Figure 1.30. Scene at a banana packing house where fruit are washed, culled, graded, and packed for distant shipment.

Fruit storage temperature is dependent on species and cultivar. If possible, fruit is stored around 32°F, as it will last the longest at this temperature. Some fruits are susceptible to chilling injury, which manifests itself as internal breakdown, surface pitting or browning, or other disorders, after storage at low, nonfreezing temperatures. The best example of this is the rapid browning that occurs in bananas when placed in the refrigerator (Figure 1.31). Many tropical fruits cannot tolerate temperatures below 45°F without chilling injury. Controlled atmosphere storage (called CA storage) is used for some fruits (mostly apple), where the O2 level in the storage room is lowered and the CO2 raised to inhibit fruit respiration and subsequent breakdown. Some apples can be stored for 1 year using CA storage.
banana chilled 24hr

Figure 1.31. A banana stored at room temperature (above) and one stored at 40°F for 24 hours (below). Chilling injury has occurred to the lower fruit, evident as peel browning, which will get progressively worse with time.

References on harvest and postharvest handling of fruit crops:

Mitra, S.K. (Ed). 1997. Postharvest physiology and storage of tropical and subtropical fruits. CABI, Wallingford, UK.

Salunkhe, D.K. and S.S. Kadam (eds). 1995. Handbook of fruit science and technology. Marcel Dekker, New York.

Snowdon, A.L. 1990. A color atlas of post-harvest diseases and disorders of fruits and vegetables. Vol. 1: general introduction and fruits. Wolfe Sci. Publ., London.

Thompson, A.K. 2003. Fruit and vegetables: harvesting, handling, and storage. Blackwell Pub., Oxford, UK.

CONTRIBUTION TO DIET, FOOD USES

Fruits are an essential component of a healthy diet, being high in vitamins A and C, low in calories, and high in fiber. Nuts are packed with protein and nutrients, but are generally high in fat and therefore calories. In this section, I have listed the nutrient composition of various fruits and nuts, and give the percentage of the recommended daily allowance (%RDA) for each vitamin or nutrient. This is based on the Food and Drug Administration guidelines for a 150 lb adult male, assuming a 2700 calorie/day diet. Also listed are the major food uses, and the utilization statistics (i.e., %fresh vs % processed), largely based on USDA data.

References on dietary value, consumption, and food uses:

Hansen, R.G., B.W. Wyse, and A.N. Sorenson. 1979. Nutritional quality index of foods. AVI Publ., Westport, Conn.

Lapedes, D.N. (Ed). 1977. McGraw-Hill encyclopedia of food, agriculture, and nutrition. McGraw-Hill, New York.

Morton, J.F. 1987. Fruits of warm climates. Julia F. Morton, Publ., Miami, FL.

Schneider, E. 1986. Uncommon fruits and vegetables: a common sense guide. Harper & Row, New York.

US Census Bureau. 2001. Statistical abstract of the United States.

http://www.census.gov/prod/www/statistical-abstract-us.html