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 RESULTS OF A PREHARVEST DROP CONTROL EXPERIMENT WITH McINTOSH APPLES 



Since the failure of 2,4,5-TA to satisfactorily control preharveet drop of 

 Mcintosh in 1955 there has been much speculation concerning the future of this 

 material ,_ Consequently, additional attempts were made in both 1956 and 1957 to 

 compare 2,4,5-TA with other materials or their combinations to determine whether 

 or not failure of 2,4,5-TA in 1955 was just a chance happening. Ofcourse, extent 

 of fruit ripening from stop-drop hormones must be considered, also. 



In 1956 we had a moderate crop plus a cool, late growing season and fruit 

 drop was of minor importance. All materials were reasonably effective. However, 

 two applications of 20 ppm of NAA gave somewhat better drop control than one 

 application of 2,4,5-TA. Neither treatment had any appreciable influence on 

 fruit ripening in 1956. 



This fall, with a large crop and a very dry year it seemed likely that a 

 much heavier drop of Mcintosh might be expected than occurred in 1956. Conse- 

 quently, a stop-drop test was set-up in the hope of getting additional comparisons 

 among materials. In Table I are data obtained from our 1957 experiments. 



Table I. The influence of several materials on the rate of preharvest fruit 



drop of Mcintosh apples. 1957 



Date Av. Cumulative Percentage of Drop Ave. Flesh 



"I trees per treatment 

 Av, yield per tree - 37,8 boxes. 



From the data presented it appears that 2 applications of NAA at 20 ppm 

 (treatment 2) will give as good or better control of drop than any other material 

 or combination of materials tested. Treatment 2 was also about twice as effec- 

 tive as 2,4,5-TA over a 3 week period. Use of Tween 20 as a wetting and penetra- 

 ting agent seems to increase the ability of 2,4,5-TA (treatment 6) to control 

 drop but appreciably increases the ripening influence of the compound. 



