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10 CIRCULAR 685, U. S. DEPT. OF AGRICULTURE 
necessity for using two applications on most summer varieties. Be- — 
cause of the relatively long effective period of the sprays on such | 
varieties, timing the application is accordingly less difficult. = 
Cost would doubtless be one of the factors in determining the 
feasibility of making two harvest spray applications. As pointed 
out previously (p. 5), no inflexible recommendation can be made 
regarding spray concentration, yet it may be seen in table 2 that very 
effective control of fruit drop was obtained in all cases where two 
half-strength (5 p. p. m.) applications were used. Obviously the 
cost of spray material would be the same as for a single full-strength 
spray application. 
‘THOROUGHNESS OF COVERAGE 
Harvest sprays to prevent abscission of fruit should for best results 
be applied to the fruit stem at or near the point of abscission. When 
applied to the fruit stem and cluster base of Delicious apples (7), 
these materials were far more effective in retarding fruit drop than 
when applied to the calyx end only. The lack of transmission of 
effect to fruit only short distances away from sprayed leaves suggests 
that leaf coverage is not particularly important. It is certain that 
sprays applied to entire large limbs have no observable influence on 
the fruit of adjacent limbs. 
In applying harvest sprays, every effort should be made to do a 
thorough job, particularly in the top of the tree, since the best fruit is 
usually borne in this part of the tree. Also, when an apple falls from 
the top it is likely to knock off other fruits on the way down. A tree 
should be sprayed from both the inside and the outside. It is difficult, 
if not impossible, to cover adequately a heavily loaded tree from the 
outside only. The fact that the spray solution is dripping from the 
foliage is no proof of thorough coverage; each fruit stem must be hit. 
Adequate coverage is not as difficult to obtain with long-stemmed 
varieties. such as Williams, Rome Beauty, Delicious, and Golden Deli- 
cious, as with short-stemmed varieties. With the long-stemmed varie- 
ties it is relatively easy to reach the stems with the spray solution, and 
the fruit hangs in such a manner that during the process of spraying 
the stem cavity often becomes filled with the spray; this insures ideal 
coverage. McIntosh and York Imperial are examples of short-stem- 
med varieties with the fruit usually clustered in such a way as to make 
it difficult to reach the stem with the spray. Only a very thorough 
and systematic job of spraying will be effective on varieties of this 
type. 
It is not possible to make any definite statement about the amount 
of spray solution required, because of differences in operators and 
equipment, as well as conditions under which the spray is applied. 
As a general rule, however, about 1 gallon of spray solution for each 
bushel of fruit is essential for satisfactory coverage. At Beltsville 
(2), 12-year-old Delicious trees received a light spray application of 5 
gallons of 5 p. p. m. concentration per tree. Another group of trees 
of the same variety received the same concentration, but a more 
thorough application, 10 gallons per tree. In general, the hight apph- 
cation proved to be just half as effective in retarding drop. These 
results serve to emphasize that the control of fruit drop can be no 
more effective than the coverage given. 
