6 CIRCULAR 685, U. 8. DEPT. OF AGRICULTURE — 
Taste 1.—Relation of concentration to effectiveness of harvest sprays on 
apples—Continued 
| | 
Spray State and | Spray State and 
Variety concen- Fees ae literature Variety concen- | qoppls literature 
| tration |CTOPP reference | tration | de ihe reference 
ese m Be | P.p.m.| Percent | 
1.3 | 
ee a eta || Pa a Delicious_.__- | 25) 70 |stariand (). 
Sane tr ae ae 5.0 5.0 
'L 10. 13. 0 13.0 
lf 0 15.7 | 1) Oe ee 3.0 | 10.0 ee 
| ie Massachusetts = 
Do SSS | oO. 0 14. 0 if (23). | 6. 0 8. ‘ bs 
10. 0 12.3 10.0 6.6 
i{ 0 19.3 a Ores 3S. 0 
if Fagen 5.0 6.6 Do. | | Stayman Wine: 5.0 | 161 ig Maryland (2). 
| “oO 284 Massachusetts ine | O | 30.0 
Dose sets % | 5.0 9. 5 (91). Bgee see 5.0 EGE 8 
Ll 10.0 6.5 | 10.0 6.5 
HS 20s Siete Dhar et TA? Tot Sc ae AD 
Bo... 10.0} 99 is pe ee Winesap_______ 2.5.) . 40 BS 
{20.0 7.4 | 5.0 | 3.0 
| 0 17.0 0 | 17.2 
lini Aap 1.4 | | 3.0°| 9.3 || Massachusetts 
Delicious______ 5.0 | 56 pare (2): DQ sae 6.0 | 9 4 Mi (22). 
10.0 4.4 Il 100] 22 
It may be seen in table 1 that while concentrations as low as one- 
fourth strength (2.5 p. p. m.) resulted in an appreciable reduction 
in drop of later varieties of apple, increasing the concentration 
generally gave more effective control. The results of various experi- 
menters, working with a number of varieties, substantiate the earlier 
conclusion (7) that as the concentration is increased the benefit de- 
rived from this increase becomes less. In some instances little or 
no benefit has resulted from increasing the concentration from 5 to 
10 p. p. m., while in other cases the stronger spray resulted in appre- 
ciably greater effectiveness. Southwick (2 2) found double-strength 
sprays (20 p. p. m.) somewhat more effective than full-strength (10 
p- p.m.) with McIntosh and Wealthy. Still further retardation in 
dropping of Wealthy was obtained by this investigator when a 
quadruple-strength spray (40 p. p.m.) was applied. It may be seen 
from table 1, however, that under many conditions a half- -strength 
spray (5 p. D. m.), if correctly timed and thoroughly applied, will 
often give effective control of dropping. Increasing the spray con- 
centration above 10 p. p. m. may prove desirable under some condi- 
tions, but generally the small added benefit would not seem to be suf- 
ficient to justify the expense. 
Tore or APPLICATION 
During the last 3 years of experimentation it has become increas- 
ingly evident that timing is the most important single factor in the 
success of harvest sprays. Early experiments (7) were directed 
toward finding the most effective time of application. In 1939, from. 
experiments involving a number of varieties, it was found that the 
effect of harvest sprays on most varieties usually reaches a peak in 5 
or 6 days after application and may continue very effective for 10 — 
days to 3 weeks, varying somewhat with such factors as tree condition 
and temper ature and consider ably with the variety; after this period 
the effect is rather quickly dissipated. Consequently, as a general 
rule, it is best to apply the sprays at the very beginning of drop in 
order to utilize their period of greatest effectiveness. If the spray 
