uf 
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ia 
the plant cell as nondissociated molecules. The increased dissociation 
of the «-naphthaleneacetic acid in a more alkaline solution resultin 
ee: 
| effectiveness reported (26,79). It is well known that harvest sprays 
HARVEST SPRAYS FOR THE CONTROL OF FRUIT DROP 13 
from the addition of lime may possibly be responsible for the reduce 
are highly effective in many instances when applied to trees carrying 
- a heavy deposit of spray residue containing lime. In such cases, how- 
ever, this previously applied lime had probably been converted to the 
carbonate form and would be relatively inert in its effect on subsequent 
applications of harvest sprays. 
VARIETAL RESPONSE 
The duration of effect as well as the degree of effectiveness of harvest 
? sprays varies considerably with the variety. While no inflexible clas- 
sification of varieties with respect to response is possible, yet it is 
apparent from both experimental and commercial results that the 
- most outstanding results have been obtained with summer varieties, 
particularly Williams, Early McIntosh, and Oldenburg (Duchess). 
Harvest sprays, when properly timed and thoroughly applied, have 
been generally effective with Delicious, McIntosh, Stayman Winesap, 
Winesap, and Rome Beauty. It should be pointed out, however, that 
with these varieties great variation in results of spraying has been 
- obtained, and in a number of instances failure to obtain control of 
drop has been reported. Results with late-fall varieties, such as Bald- 
win and York Imperial, have been generally unsatisfactory, although 
under certain conditions satisfactory results have been obtained (7, 
14). The usual better response of summer varieties is probably due in 
part to the more active growth status of the tree at the time the fruit 
is maturing. Also the higher temperatures (p. 11) prevailing at the 
time of and after the spray application may play a contributing part. 
Harvest sprays seem te be less effective under conditions when or 
on varieties in which the drop is spread over a rather extended period. 
In such instances it becomes more difficult to time properly the spray 
application. The harvest drop of York Imperial and McIntosh in 
southerly regions is characteristically of this type. 
TREE VIGOR 
Hoffman (7/7) and Southwick (20) have shown that vigorous Mc- 
Intosh trees with a relatively high nitrogen content tend to have a 
heavier preharvest drop than trees growing at a lower nitrogen level. 
These investigators point out that such practices as heavy nitrogen 
fertilization, heavy mulching, and late cultivation may tend to increase 
the preharvest drop of this variety. Whether or not this relation 
between nitrogen level and harvest drop holds with other varieties 
is not known. 
There seems to be no definite evidence available indicating the rela- 
tion between tree vigor or nitrogen level and effectiveness of harvest 
sprays. It is known, however, that good success with these sprays 
is dependent on a normal, actively functioning foliage system. If 
_ sprays are applied late in the season on late-fall varieties after the 
foliage has begun to turn, little effect may be obtained. Failure in 
such cases may possibly be due to both the cool temperature and the 
foliage condition generally prevailing at the later dates. 
