SPRAYING TO CONTROL APPLE DROP 13 



Addition of Oil 



III 1939, tiardiicr, Martli, and Batjer (2) reported increased effectiveness 

 ot drop control sprays when a small amount of oil was added. Since it 

 seemed that even a small quantity of oil might act as a spreader and 

 improve coverage, it was included in some tests with Mcintosh. The 

 addition of a summer oil (1 pint per 100 gallons) had an effect similar to 

 that reported above. For example in one test, using 10 p. p.m. of hormone, 

 tlie dropping amounted to 10.2 and 14.1 percent respectively witli and 

 witliout oil. Tlie check trees dropped 24.3 percent. Furtlier work nui\ 

 indicate that the use of oil may compensate in part for decreased hormone 

 concentrations. At the present time, however, it should be considered as 

 a supplementary procedure to enhance the action of the hormones. Its 

 use should not affect apples in appearance, quality, or storage ability. 



Importance of Size of Crop 



It lias already l)een suggested that the amount of fruit on a tree may be 

 a deciding factor in determining the advisability of using a hormone spray 

 It) lessen dropping. The grower is interested in actual bushels, not in 

 mere percentages. Percentage figures in themselves, as related to dropped 

 aijples, mean little in terms of monetary gains or losses. However, when 

 a grower reads that a hormone spray has reduced drop by 10 percent, he 

 immediately associates this percentage figure with an arbitrary orchard or 

 acre yield, or possibly with the known performance of his own trees. The 

 "10 ])ercent" then becomes "bushels per tree" or "bushels per acre" and 

 lias a definite meaning so far as that grower is concerned. Other growers 

 will interpret differently as a result of different yield standards. Thus, 

 with a 200-bushel yield per acre, a reduction in drop from 15 to 5 percent 

 means a saving of 20 bushels. Such a reduction with a 600-bushel yieUl, 

 on tiie other hand, gives a saving of 60 bushels per acre — an increased 

 saving of 40 bushels. Hence, it is evident that size of crop is especially 

 significant in the economical use of hormone sprays. The heavier the 

 \ield, tlie more jiistification there is for a hormone application. 



Orchard Variability 



.Since the purcliase of liormones and their application cost considerable 

 money, it is wise for each grower to consider carefully to what extent 

 this method of decreasing drop should be utilized under iiis particular 

 conditions. No two Mcintosh orchards are alike. Even similar appear- 

 ing orchards in close proximity often behave differently in regard to pre- 

 liarvest dropping of fruit. This same variability may e.xist among neigh- 

 boring trees in a single block. It has been shown also that severity ol 

 droj) with Mcintosh may be associated with a high state of fertility, 

 esijecially in relation to nitrogen. These relationships have been discussed 

 fully in a previous publication (6). Briefly, when available nitrogen is 

 jjlentiful and trees are in a vigorous state of growth, more severe pre- 

 harvcst dropping of apples is likely to occur than when trees are grown 

 on the "liard side." Since good vigor is essential for high production, a 

 method to reduce premature dropping other than by decreasing vigor is 

 ol paramount significance. The use of drop-control sprays is especially 



