SUMMARY 



Efforts to reduce the economic loss caused by 

 fruit falling from trees at harvest have gained out- 

 standing success with apples and pears. 



Four plant growth-regulating compounds in dilute 

 sprays are being widely used by growers to retard the 

 natural loosening of fruit on the tree. Each compound 

 has merits, also limitations, in use. 



NAA (naphthaleneacetic acid) controls drop of all 

 commercial varieties of apples and pears. It is the 

 only fruit-sticking chemical found practical for air- 

 plane spraying. Its effectiveness is usually no longer 

 than 10 days or 2 weeks. 



2,4-D (2,4-dichlorophenoxyacetic acid) controls 

 drop of Wine sap and Stayman apples and Bartlett pears. 

 It has such lasting effectiveness that it can be applied 

 3 to 4 weeks before harvest. 



2,4,5-T (2,4,5-trichlorophenoxyacetic acid) and 

 2,4,5-TP (2,4,5-trichlorophenoxyproprionic acid) con- 

 trol drop of all connmercial varieties of apples, but 

 are damaging to pears. Like 2,4-D, their effectiveness 

 is prolonged. 



Research has progressively added to understanding 

 of factors that affect success with these preharvest 

 sprays, including: choice of compound; solution strength; 

 timing of application; ten-iperature; moisture; and avoid- 

 ance of such side effects as overripening and soften- 

 ing of fruit and damage to foliage and buds. 



Information in this report was provided by the Horticultural Crops Research 

 Branch, Agricultural Research Service 



