profitable Fruit Growing
through better production methods
Mimeo. HO 50-3	December, 1956
what's new in ...
fruit varieties • soil management • spraying and dusting • fruit handling • fertilization • pruning and thinning • storage • marketing
PRE-HARVEST DROP CONTROL OF APPLES
The use of chemical growth regulators or "hormones" to prevent the premature dropping of apples has become an established practice in many Indiana orchards* These materials are used to prevent the normal dropping of fruits for a few days in order to obtain better color, size, and maturity or to allow greater flexibility in the harvesting of the crop*
Several materials have been used for drop control on apples and many new materials are being tested experimentally. Two materials are presently recommended for use in Indiana:
N.A.A. (Naphthalene acetic acid)
N.A.A. is the original growth regulator to be used for drop control on apples and is still used quite widely. It is effective on all varieties of apples at a concentration of 10 p.p.m. (p.p.m. a parts per million; see container label for proper dilution). N.A.A. is absorbed rapidly and becomes effective In a short time. Sprays should, therefore, be applied 2 to 3 days before drop would normally begin. Since N.A.A. is effective for a relatively short period of time, the spray application should be repeated in 7 or 8 days if the harvest must be delayed beyond that period of time. The concentration may be increased to 15 p.p.m. on McIntosh, Jonathan or Grimes, which are harder to "stick" or to lengthen the interval between sprays to 10 to 12 days.
2.4.5 - TP (2.4.5 trichloronhenoxv propionic acid)
2,4,5-TP is another growth regulator used for drop control on apples. It is effective on all varieties but must be applied further in advance of expected drop than N.A.A. since it is absorbed more slowly and, therefore, requires longer to become fully effective, Care should be taken in using 2,4,5-TP on summer varieties as it will result in direct ripening and increased color development and maturity if applied too early or at a high concentration, 2,4,5-TP remains effective for a longer period of time than does N.A.A. and a single application is usually sufficient to control drop for the entire pre-harvest period.
Applications of 2,4,5-TP should be made at least 3 to 7 days before expected normal drop at a concentration  of 10 p.p.m. for Delicious, Jonathan, Grimes and all summer varieties. For all other fall and winter varieties of apples, use 20 p,p,m, applied 7 to 10 days before drop is expected to begin.
PURDUE UNIVERSITY
Agricultural Extension Service Lafayette, Indiana Department of Horticulture