HARVEST SPRAYS FOR THE CONTROL OF FRUIT DROP ve 
| is applied too far in advance of the harvest drop the effect will be 
| largely or entirely dissipated before drop begins. An experiment 
- performed with the McIntosh variety in 1939 (7) will serve to illus- 
- trate this point. In the course of this experiment it developed that 
' spray applications had little or no effect in retarding the main har- 
/ vest drop, which began 9 to 10 days after the spray was applied. 
| When, however, spray applications were made in this same orchard 
| at the beginning of the main drop, effective retardation in drop was 
| obtained for a period of 8 days, after which a rather abrupt decrease 
~ in effectiveness became evident. 
Because of the longer effective period and somewhat greater inten- 
| sity of effect of harvest sprays on summer and some fall varieties, 
- timing of harvest sprays is not as exacting as with such a variety as 
McIntosh. With Williams, Oldenburg (Duchess), and Early Mc- 
_ Intosh the sprays may be applied several days before dropping 1s 
| expected to start, as judged by the maturity and condition of the 
- fruit. If sprays are applied on these varieties as early as 15 days 
| prior to the expected termination of harvest, good control should be 
| obtained. 
| With most fall varieties satisfactory results should be obtained if 
sprays are applied a week or 10 days before the estimated date of ear- 
lest picking maturity. In the case of McIntosh, with a relatively 
‘short period durmg which the spray is effective, it is often found 
desirable to apply the harvest spray when sound, mature apples are 
beginning te drop. This requires close day-to-day observation on sev- 
eral typical trees scattered throughout the orchard. When fruits that 
| drop just prior to the harvest period are defective in one way or an- 
_ other, the dropping of these fruits may nct be a reliable indication 
| that the harvest drop is under way. On the other hand, if spray ap- 
plication is delayed until the dropping of sound, mature fruit has be- 
“come conspicuous, the treatment may be too late to retard the proc- 
_ esses that resuit in fruit drop. 
_ In order to ascertain if it is possible to stop fruit drop once it is 
well under way, Batjer and Marth (2) applied a spray of 5 p. p. m. 
-concentration to McIntosh trees at Beltsville after the accumulated 
fruit drop had reached 15 to 380 percent. The results of this test showed 
_élearly that the spray was not effective, since fruit drop continued 
at about the same rate as if no spray had been apphed. Southwick 
and Shaw (23) in one experiment with McIntosh reported continued 
heavy drop after applying half-strength and full-strength sprays to 
m trees that had an accumulated drop of 10 to 15 percent prior to the 
time the spray was applied. In another instance with this variety, 
these investigators (23) obtained an apparently significant effect from 
a harvest spray applied after a 20-percent drop had occurred. Ellen- 
wood and Howlett (5), however, failed to obtain any effect from a 
spray applied to Stayman Winesap once a heavy drop had begun, yet 
they reported good control when the spray application preceded the 
drop by a few days. Murphy (78), working with McIntosh in Rhode 
Island, obtained more effective results when the spray was applied 
September 9 than with a later application on September 13. Un- 
sprayed trees in this experiment had dropped 30 percent of their fruit 
by September 21. 
Thus it seems apparent from the evidence at hand that the effective- 
hess of harvest sprays becomes progressively less pronounced as fruit 
