SPRAYING TO CONTROL APPLE DROP 7 



When to Apply a Hormone Spray: Repeat Sprays 



It was stated that in test 3 (table 2) the September 12 spray applica- 

 tion was too early. The data show that this spray might have been de- 

 layed somewhat without undue risk. Since the effective period of a hor- 

 mone spray on Alclntosh is definitely limited, it is to the grower's advan- 

 tage to delay as long as possible before putting it on. The endeavor to 

 determine the proper time showed that there are many considerations 

 which may upset any hard and fast rule. It must be remembered that 

 when the retarding effect of tlie hormone wears off, dropping may be 

 sudden and severe. This evidently happened after October 1 with Mc- 

 intosh in the tests reported in Table 2. Despite the second application on 

 September 28, heavy dropping resulted. In fact, the increase in dropping 

 was relatively larger with the sprayed trees than with the checks. A 

 repeat application on October 2 on a few trees in one of the tests had a 

 slight influence but was unsuccessful in materially slowing up the severe 

 rate of dropping. The failure of repeat sprays with Mcintosh is also re- 

 ported by Batjer and Marth (1) who offer the explanation that when 

 abscission has progressed beyond a certain stage spray applications of 

 hormones will not retard the process. 



With some varieties, a repeat spray closely following the initial spray 

 increases effectiveness of drop control (2). This probably is due to a 

 "building up" of protection or to a more complete coverage. However, 

 with Mcintosh in 1940 repeat sprays did not prove particularly advan- 

 tageous. In Table 2, it is difficult to see any added beneficial effect of the 

 September 17 application (treatments (a,) and (c)). The accumulated 

 drop to September 30 for the trees receiving this application was just about 

 equal to the drop of the trees which had had only the September 12 spray 

 (treatments (b) and (d)). The application on the 28th, of course, had not 

 become effective. In another test with 10 large trees per treatment, re- 

 sults were as follows: 



2 sprays (10 p. p.m.) 3.1 percent drop 



1 spray (10 p. p.m.) 4.4 percent drop 



Check .^. 19.9 percent drop 



Here, the repeat spray, 6 days after the first one, did have a beneficial 

 effect, but it was of minor importance. However, in Rhode Island (S), 

 a second application 6 days after the first seemed to increase by 4 days 

 the period of effectiveness. Batjer and Marth (1) found that a repeat 

 application (in 7 days) increased the effective period only 1 to 1^ days 

 longer than the single application treatment. They found little added 

 benefit from smy sprays following the initial application. Additional data 

 on this point may be needed, but the evidence at hand seems to show that 

 repeat applications, at least with Mcintosh, are hardly warranted. 



It is evident then, that with Mcintosh it is doubly important to determine 

 the best time for hormone spray applications. On the basis of the evidence 

 to date, it would seem advisable to wait until the preharvest drop has 

 begun and then to apply one spray only. The dropping of injured or 

 wormy apples at this season should not be used as a certain indication that 

 preharvest dropping has definitely commenced. When average-sized, well- 

 shaped, sound, clean apples have begun to drop in any quantity — 20 to 25 



