SPRAYING TO CONTROL APPLE DROP 9 



should be noted that the average dropping percentages of the sprayed and 

 the check trees in each case were practically equivalent up to October 2. 

 Although the actual yields are not the same, estimates of the drops per 

 acre based on these yields are given. Under conditions of these tests, a 

 saving of about 50 bushels per acre could be attributed to the late hormone 

 spraying. These estimates are based on 27 trees to the acre for the large 

 trees and 50 trees to the acre for the smaller ones. Of course this arbitrary 

 analysis is for comparative purposes only. No two tests could be expected 

 to give identical net results. Thus, if the above yields had been higher, the 

 benefit froin spraying would have been enhanced. 



Two other tests were conducted where spraying was delayed even longer 

 than in the above cases. There was some effect from these applications, 

 but the results probably did not justify the cash outlay and the time ex- 

 pended. Furthermore, the data indicate that the effectiveness of a hormone 

 spray application on Mcintosh may be progressively less pronounced as 

 the crop becomes more and more mature on the tree. Involved, of course, 

 is the question of decreasing temperature means as the season progresses. 

 Late spraying of York Imperial and Rome Beauty in Maryland (1), Bald- 

 win in Rhode Island (5), and Baldwin at Ainherst was generally unsuccess- 

 ful in lessening subsequent dropping. This possibly may be explained on 

 the basis of the low physiological activity of the tissues of the tree late in 

 the fall. Without ignoring the question of variety itself, the above argu- 

 ment is supported by the fact that early apples usually are more likely to 

 react favorably to hormone applications than late varieties. 



It is a widely accepted fact that losses from preharvest dropping of Mc- 

 intosh were, in general, less pronounced in 1940 than in many previous 

 years. This was certainly true in Massachusetts. As a result, several 

 investigators have concluded that the response of Mcintosh to hormone 

 sprays in 1940 may not represent a true index of response for a normal sea- 

 son. August and September were relatively cold months, the Amherst 

 mean temperatures being respectiveh^ 1.7° F. and 1.6° F. below normal. 

 That the effectiveness of the hormone in a spray is influenced greatly by 

 differences in temperatures at a critical time has not been proved, but may 

 offer one explanation for certain differential results. It has been observed 

 that high temperatures at this season increase preharvest dropping of 

 apples. This is discussed at greater length in a previous publication (6). 

 It is sufficient here to emphasize the important influences which temper- 

 ature may have on drop. With high temperatures, which favor dropping, 

 the usefulness of hormone spraj's may be enhanced. 



Effect of Concentration 



The amount of active hormone in the spray solution seems to be very 

 important. The proprietary commercial hormone preparations on the 

 market last season were designed to furnish 10 parts of hormone per mil- 

 lion parts of water when the manufacturer's recommendations were fol- 

 lowed. This is a .001 percent concentration. Table 4 summarizes results 

 secured as a result of reducing the hormone concentration. Three com- 

 mercial preparations were used. In every case, some decrease in effective- 

 ness resulted from the use of the lower hormone concentrations. 



This finding is substantiated, in general, by results elsewhere. Gardner, 



