CoNTENTS 
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Summary and conclusions___--_-_------___-___- 2| Factors influencing effectiveness on apples— 
Harvest drop a serious problem_________________ 3 Continued. 
Effectiveness of various chemicals on apples____ 4 Varietal. response = 3 a eee 13 
Source o1spray-materialss =. ke 5 ‘Preé Vis0r =. 22 Ss 2 Ae ed ee ee ee 13 
Factors influencing effectiveness on apples_____ 5 Soil moisture = ae ee eee 14 
encentnalion ssn Ses a ee oe 5 | Relation of harvest sprays to fruit maturity____ 14 
ABINEIO ASD liCatIO Naat sen eee em eek Bee 6| Application of harvest-spray substances by 
Number of applications. _.---- =.= = 8 dusting =< 2°) S222 Se ee oe eee 14 
‘Thoroughness of coverage- -____---__--___---- 10 | Effectiveness of harvest sprays on pears________ 15 
Rain alter, application a= = 2s ee 11 | Effectiveness of harvest sprays on apricots and 
Memperatare ss hse Fe eet ge 11 PEACHES 23 sae ey ee ee 15 
Compatibility of harvest sprays with other ‘Literature-cited 92-2 are a ae 15 
Spray aaterials: oe des ee sip Awe te 11 
SUMMARY AND CONCLUSIONS 
Numerous investigators and fruit growers have obtained profitable 
results by spraying orchard trees at harvesttime in order to control 
fruit drop—a control measure first used commercially in 1940. This 
practice now promises to bring considerable savings to many fruit © 
growers and the Nation; it is therefore important that the experience 
of those who have studied and practiced the use of harvest sprays 
should be generally known, both by growers and by horticultural 
investigators. The results of various investigations seem at present — 
to warrant the following conclusions: 
Properly used harvest sprays are very successful with many vari- 
eties of apples. a-Naphthaleneacetic acid, «-naphthaleneacetamide, 
and the sodium salt of e-naphthaleneacetic acid are equally effective in 
retarding fruit drop. : 
Half-strength sprays (5 p. p. m.) are adequate for most summer va- 
rieties of apples, and when apphed under favorable conditions have 
given effective control of dropping with many fall varieties. Full- 
strength sprays (10 p. p.m.) have proved desirable and may be neces- 
sary for fall varieties under many conditions, but generally the small 
added benefit would not seem to be sufficient to justify the increased 
expense. 
Time of application is the most important single factor in the suc- 
cess of harvest sprays, but thorough coverage to reach the fruit stems 
is also essential. Generally 1 to 3 days are required for these sprays 
to become effective. Intensity of effect usually reaches a peak in 5 
or 6 days and may remain at a high level for 10 days to 3 weeks, vary- 
ing with such factors as variety, tree condition, and temperature; 
after this period the effect is rather quickly dissipated. Consequently, - 
as a general rule, the sprays are most effective when applied at the © 
very beginning of the harvest drop. If these sprays are applied too ~ 
far in advance of drop or are delayed until drop is well under way, 
little or no effect may be realized. a 
If harvest sprays are properly timed and thoroughly applied a 
single application will usually give all the protection it is possible to — 
achieve. A second application 4 to 6 days later, hosvever, is recom- — 
mended for some varieties and under conditions where exact timing is © 
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