HOfilvIGIjaS FOR ?KE-HARVES'f DROP CONTROL 



We now have two materials that may be used for pre-harvest drop control: 

 (1) the standard naphthaleneacetic acid (N.1A), or (2) 2,U,5-trichlorophenoxypro- 

 pionlc acid (2,li,5-TP). Also, 2,U,5-TP is of interest to some because of its 

 possible influence on color and maturity. Since the use of these materials depends 

 upon one's objectives, it is best to consider their use under two headings. 



1. YJhere Drop Control is the Primary Objective . 



A. On Mcintosh both materials should be used at about the time the drop 

 of sound apples commences. 



B. 2,U,5-TP will delay drop longer than NAA materials but growers should 

 pick Kclntosh trees sprayed with either hormone before they get too ripe if one 

 wishes a good storage apple. 2,U,^-TP may delay drop 3 weeks, as compared to 7-10 

 days for NAA materials. Fruit sprayed with 2,U,5-TP should probably be picked 

 within about 2 weeks after spraying in order to have a good storage apple, 



C. Because of the inherent ripening possibilities followdug the use of 

 materials containing 2,U,5-TP, MA is still advised where it has given satisfactory 

 drop control. Also, with a relatively short crop of Mcintosh, the need for extended 

 drop control is not as essential as in a heavy crop year. 



D. 2,U,5-TP should be used at a concentration of 20 ppm and no higher 

 on our varieties. It may be concentrated safely up to 3X. 



E. On late varieties, such as Baldwin, which may drop badly in some 

 years, 2,ii,^-TP does not have to be as carefully timed as it needs to be with_ 

 Mcintosh. On Baldwin an application 2 to 3 weeks aliead of harvest may be satis- 

 factory and desirable (since foliage may be injured from frost or quite senescent 

 in October) without influencing maturity very much. 



F. Some formulations of 2,ii,5-TP have been changed this year. One 

 common commercial brand has been doubled in concentration. In other vrords, one may 

 need only U oz. per 100 gallons to give a 20 ppm solution as compared to 8 oz. a 

 year ago. Remember to read the label . It takes about 8 grams of actu al 2.It,5-TP 

 per 100 gallons to give a 20 ppm spray . 



2, Where Hastening Maturity and Improving Color with 2,U,^-TP is the Objective . 



A, In 1952, with a short Mcintosh crop, it would appear that interest in 

 this would be less than a year ago. .However, some may wish to use it for this 

 purpose on other varieties. Early Mcintosh apparently responds quite vrell. Its 

 effect on Duchess, Gravenstein, and Milton is not too favorable. In some instances 

 2,U,5-TP has stimulated ripening and color development of Baldwin and Golden 

 Delicious, 



B, Treatment with 2,U,5-TP should be used at the same concentration 

 (20 ppm) as is used for pre-harvest drop control. Apply the material at least 

 3 -vreeks ahead of harvest on early and midseason varieties and from 5 to 6 weeks 

 ahead of harvest on late varieties. In general, the earlier it is applied the 

 greater the coloring and ripening effect at a given calendar date thereafter. 



C, The fruits will ripen unevenly. Some apples will be much more mature 

 and better colored than adjacent fruits on the same tree. Keep your eyes open for 

 over-ripeness, water core, and an increase in cracking of the fruits wiiere this 

 material is used. 



