HARVEST SPRAYS FOR THE CONTROL OF FRUIT DROP 3 
difficult or problematical. By making two applications (the first a few 
_ days ahead of the expected drop), the chances of hitting the fruit at 
the most receptive period are of course greatly increased. 
The addition of small quantities of summer oil (1 pint to 1 quart 
per 100 gallons) has generally resulted in slightly increased effective- 
_ness of harvest sprays. 
Harvest sprays are more effective when applied at relatively high 
temperatures (80° to 85° F.) than when applied under cooler condi- 
tions (55° to 60°). A somewhat higher spray concentration might 
be used on some varieties on days or parts of days when the tempera- 
ture is relatively low. 
No direct effect of harvest sprays on fruit maturity has been re- 
ported. Fruit receiving harvest sprays, however, should not be al- 
lowed to remain on the tree too long after the normal harvest period, 
since it may become overmature. 
Promising results with harvest-spray substances applied in dust 
form to McIntosh apples have been obtained. The chief advantage 
of dusting would seem to be the rapidity and uniformity with which 
applications could be made. 
Results with harvest sprays on pears, particularly the Bartlett 
and Bose varieties, have been generally satisfactory. The time of 
application, spray concentration, and duration of effect are essen- 
tially the same as for most varieties of apples. 
| Harvest drop of stone fruits is not generally a serious problem. 
With apricots the use of harvest sprays has reduced the subsequent 
fruit drop, whereas with peaches no appreciable effect has been 
obtained. 
=~ 
HARVEST DROP A SERIOUS PROBLEM 
Losses as a result of preharvest and harvest drop have long been a 
serious problem of apple and pear growers. As the fruits approach 
picking maturity they tend to loosen from the spur and considerable 
quantities may drop prior to and during the picking operation. Such 
fruit is badly bruised and if salvaged at all has a low value compared 
with that picked from the tree. This tendency for fruits of many 
varieties to loosen and drop as they approach proper picking maturity 
has led growers to advance the picking dates in some instances, with 
reduced color, reduced size, and poorer storage quality as possible 
results. 
Such fruits as Bartlett pears and summer and fall varieties of ap- 
ples generally are increasing in size and weight at the time they are 
harvested. Therefore, early or immature harvesting of the crop may 
appreciably reduce total tonnage. 
In 1939 it was shown by Gardner, Marth, and Batjer (7)! that a 
group of chemical compounds, generally referred to as growth-regu- 
lating substances or hormones, when used as sprays in dilute concen- 
trations, would inhibit abscission and thus effectively retard the pre- 
harvest drop of apples. After this discovery, proprietary prepara- 
tions containing the effective substances were made available to fruit 
growers. In 1940, the first year of commercial use of harvest sprays, 
1 Italic numbers in parentheses refer to Literature Cited, p. 15. 
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