PRSHARVEST DROP CONTROL 



It is now evident, barring a major catastrophe, that a very large crop of 

 apples is to be harvested in Massachusetts, You recall that with a similar crop 

 in 1955 an exceedingly heavy preharvest drop was experienced. 



Mcintosh . In August of 1955 we had considerable faith in 2,4,5-trichlorophenoxy- 

 acetic acid (2,4,5-TA) for preharvest drop control of Mcintosh, but by mid- 

 September much of our faith in it was lost. The reason for the failure of 2,4,5- 

 TA to control drop in 1955, when both naphthaleneacetic acid (NAA) and 2,4,5- 

 trichlorophenoxypropionic (2,4,5-TP) were effective, is still not definitely known. 

 In 1956 we tested 2,4,5-TA again in hopes of determining whether this material 

 would be as effective as it appeared to be prior to 1955. However, the 1956 

 season was not a good year to test preharvest drop control materials. Because of 

 a cool growing season, last year's harvest period for Mcintosh was 7 to 10 days 

 later than usual in most sections and no serious fruit drop developed on Mcintosh 

 until late September or early October. Under these conditions 2,4,5-TA reduced 

 fruit drop about 50 percent. Even so both NAA (2 applications) and 2,4,5-TP were 

 slightly superior to 2,4,5-TA in this regard. 



If Mcintosh fruit drop is no more serious in 1957 than in 1956, then 2,4,5-TA 

 would probably be a suitable material. It controls fruit drop for 3 to 4 weeks 

 when effective and does not hasten fruit ripening to a marked degree. It is 

 our guess, however, that Mcintosh fruit drop will be more of a problem in 1957 than 

 it was in 1956. 



Since 2,4,5-TA appears to lack the reliability of HAA we believe that 20 ppm 

 of NM is generally the best material to suggest for Mcintosh drop control in 

 1957. For drop control beyond 10 to 12 days, growers will have to apply HAA at 

 least twice at / to 10 day intervals. For those who wish to try 20 ppm of 

 2,4,5-TA in hopes that a single application of it will be satisfactory, we 

 suggest that you watch fruit drop very carefully following its use. If drop 

 control is not evident 5 to 6 days after its application, NAA should be applied 

 immediately. 2,4,5-TP is not recommended for drop control of Mcintosh unless 

 they are picked within 2 weeks after it is applied, because of its strong tendency 

 to hasten fruit ripening. 



Early Apples. NAA materials are generally satisfactory for drop control of early 

 apples . 2,4,5-TP has a strong tendency to increase the rate of fruit ripening. 

 In some cases it may hasten the development of red color but sometimes the 

 influence on ripening is so pronounced that the fruit may become too soft for 

 sale. 2,4,5-TA does not appear to be reliable for drop control of early apples. 



Late Apples . For drop control of late apples (Baldwin. N. Spy, Delicious, and 

 Rome) 20 ppm of 2.4.5-TP is outstanding. It will often control fruit drop for 

 about 4 weeks after the time of application and generally it doesn't hasten the 

 rate of fruit ripening of these late varieties appreciably. Be sure to get this 

 material on the trees while the foliage is in a good healthy condition. If foliage 

 is injured by a frost after this material is applied, good drop control will be 

 obtained. On the other hand, if the foliage has been injured by frost, mites, or 

 magnesium or potassium deficiencies prior to a hormone application, any material 

 may be completely ineffective. ;^ • 



---F. W. Southwick 



I I I 11 I I I I t I I 11 I I 



