Fruit drop

One of the economically most important areas in the control of plant processes is defoliation—the intentional removal of leaves. Large quantities of several chemicals currently are employed for this purpose, including magnesium chlorate and DEF (S,SyS-tributyl phosphor otrithioate), and the principal commercial value is for defoliation of cotton. Several synthetics such as 4-chlorophenoxyacetic acid and naphthalene-1-acetic acid are used to provide the opposite but related effect of retarding or limiting fruit drop in apples, stone fruits, and grapes. 

The phenomenon of leaf and fruit drop is known as abscission and has been suspected for some time to be under hormonal control. Dr. Addicott s description of the structure and properties of Abscisin II, the abscission hormone isolated from cotton, climaxes over 12 years of his own investigations on the subject and represents perhaps the greatest advance in plant hormone research in the past decade. It also provides an unusual and unsuspected structural model to guide... 

In a good year, some cultivars will set a great deal of fruit so much so that the weight can break branches. In such years, after the natural fruit drop in early summer, thin the remaining fruitlets with scissors to about 2-5 in (5-10 cm) apart. 

Thompson, C. R., and O. C. Taylor. Effects of air pollutants on growth, leaf drop, fruit drop, and yield of citrus trees. Environ. Sci. Technol. 3 934-940. 1%9. 

In summary, oxidant stress reduced water use and photosynthesis, increased leaf drop and fruit drop, and resulted in a severe reduction in yield of marketable fruit. All these effects occurred without the development of plainly visible leaf symptoms. 

Several inferences can be drawn from these data that may suggest the impacts to be expected at the consumer and decomposer levels. Accelerated leaf drop may influence the development of pests—namely, aphids, scale insects, and red citrus mites. Pest populations might be increased if injured leaves had higher concentrations of amino acids or free sugars before abscission (see Chapter 11) or diminished if leaves fell too rapidly. Leaf and fruit drop would provide a larger substrate for populations of decomposer organisms at the soil surface. 

The commercial use of 2,4-D has decreased substantially and (ca 1993) it has general use for home lawns to control broadleaved weeds it also is used on a limited basis to control broadleaved weeds in commercial moncotyledonous crops, eg, sugarcane. 2,4-D is used on citrus when the fruit is 1/3 to 1 inch in diameter to increase fruit size and to limit fruit drop on trees more than six years old. It should not be applied to trees that are in full flush. A further use includes treatment of harvested lemons at 500 mg/L to improve storage properties and to delay yellowing (23). It is used in certain parts of the world to increase latex flow in old mbber tree plantations. 

Lactidichlor-ethyl has been used to increase yields, reduce fruit drop in apples, and increase maturity in grapes. It causes fruit drop in peaches which decreases actual number of peaches per tree while increasing yields due to larger fruit size. The mode of action is attributed to inhibition of ethylene... 

Induce or prevent leaf and/or fruit drop (abscission). 

With the exception of 2,4-D and gibberellic acid treatments of a variety of citrus crops, where improved fruit set, reduced fruit drop, and the ability to delay harvesting without loss of fruit quality are recognized benefits, few applications have been developed for the use of hormone-type regulators in tropical fruits. Recent work has shown that gibberellic acid will delay postharvest ripenining and improve the quality of bananas and that napthaleneacetic acid treatment of oil palm to delay fruit abscission has increased both yield and oil content. 

The varying sensitivity of apple cv. Coxfs Orange Pippin to ethephon applied at different times as a fruit thinning agent. ° o fruit drop during the 11 days following spraying... 

Using individual citrus trees which were exposed to clean or smog-polluted air, Thompson and Taylor (36) and Thompson et al. (37) were able to show a reduction in crop yield from trees growing in unfiltered air. They showed that the combined pollutants in smog caused reduced water use, reduced photosynthesis, increased leaf and fruit drop, and severe reduction in yield. All of these changes occurred without the appearance of any visible injury to the leaves or fruit. 

Drop, Fruit Drop and Yield of Citrus Trees, Environ. Sci. Technol. (1969) 3, 934. 

Our search for attractants is focused on the Tephritid family of fruit flies which Includes species that are of economic importance in Europe, Asia, Australia, and the Americas. It is estimated that the olive fly, Dacus oleae. causes ten percent fruit drop in European olives. Of the Infested fruit remaining on the trees, 25 percent of the flesh is destroyed (48). A conservative estimate of the annual cost of the recent Medfly infestation in California, not including capital outlays, is 59 million for chemical controls, 38 million for quarantine and fumigation, and 260 million in crop losses (49). It is estimated that 70% of the susceptible fruit in Egypt is infested by the Medfly (50) and a 50 million control program has been started there. 

There are two periods in which trees are sensitive to lack of light. The first is shortly after flowering (when lack of light results in smaller fruit and can lead to increased fruit drop in June), and the second period is before harvesting (when lack of light affects fruit growth and surface colour). 

Ripening mid-end August, spread out over a long period, more than one picking needed, tendency to early fruit drop, colour development often inadequate... 

Susceptibility some susceptibility to scab and mildew, early fruit drop Keeping quality satisfactory, until the end of October in cold storage at 3°C Red mutants Ambassy (Dalili), Davodeau Ligonniere Nursery (France) Celeste (improved standard), Herr Nursery (Germany)... 

Origin East Mailing, UK Gox Orange X Idared cross Ripening early to mid-September, tendency to early fruit drop Fruit medium size with bright red or orange-red striped colour, flattened sphere shape... 

Wiiiiams Bon Chretien good yields fruit drop... 

Herman 1st-2nd week round, dark blue, sweet, 35 g dwarfing, broad tolerant pre-harvest fruit drop, very good tor baking, better than R. Gerstetter... 

Damage Maggots tunnel through apples, blueberries, and plums. Fruit drops prematurely early cullivars are most affected. 

Life Cycle Adult beetles overwinter under fallen leaves, stones, logs, or other garden debris, flying to trees just as blossoms open adults feed and lay eggs, which hatch in 5-10 days larvae feed in fruit 2-3 weeks when fruit drops, they exit and pupate in the soil. Second generation adults emerge in late July to late October, feed on ripe or fallen fruit until fall, then move to shelter to hibernate. Up to 2 generations per year. 

Magnesium is a constituent of chlorophyll and acts as an activator of numerous plant enzymes. Thus, chlorosis in plants is an early symptom of Mg deficiency, as well as weak stalks and premature leaf and fruit drop. 

Use Selective weed killer and defoliant, fruit drop control. 

Use Growth retardant used in greenhouses, retards premature fruit drop. 

Products and Uses A fungicide, herbicide, weed killer, and defoliant that controls fruit dropping. It is used on barley (milled fractions, except flour), oats (milled fractions, except flour), potable water, rye (milled fractions), sugarcane bagasse, sugarcane molasses, and wheat (milled fractions, except flour). 

Large amounts of auxin, however, by causing increased amounts of ethylene, encourage fruit drop, and are used in the thinning of fruit in the production of apples and olives (31). 

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