PREHARVEST APPLE DROP 21 



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did not present data to show on what dates an equal amount of drop- 

 ping occurred on sprayed and unsprayed trees, which should indicate 

 the true etTective period. 



Batjer^ found that spraying with naphthaleneacetic acid with the 

 air temperature at 82° F. and 63° F. had a ditTerential etifect on fruit 

 drop with Delicious and Winesap and that the rate of drop was con- 

 siderably less following spraying at the higher than at the lower 

 temperature. However, equal amounts of drop at the two tempera- 

 tures were not more than two to three days apart. 



SUMMARY 



Although heavy- and light-dropping Mcintosh trees seemed 

 more or less segregated into groups in the orchard, dilTerences in soil 

 profile, root distribution, or number of small roots per tree were not 

 large enough to account for ditTerences in drop except that small roots 

 were more numerous in the lower levels of the soil under heavy 

 dropping trees than under light-dropping trees. 



The soil was a Charlton loam consisting of four distinct layers, 

 or zones, and an underlying hard till layer. The A and B zones were 

 weathered material, the C and D zones only slightly weathered. The 

 A and C zones were universally present. The D «one contained many 

 small and some large stones. No stones were found where the D 

 zone was absent. 



Small roots penetrated all four zones, but rarely into the till lay- 

 er except where it was closest to the soil surface. 



The density of population of small roots was greatest in the C 

 and D zones under both heavy- and light-dropping trees. 



There is some evidence that heavy-dropping trees were on 

 slightly more acid soil than light-droppers. 



The differences in amounts of available nitrogen, potassium, 

 magnesium and calcium under heavy- and light-dropping trees were 

 not sufficient to account for differences in apple drop. The phosphorus 

 content of the soil was slightly higher under the lighter droppers. 



\^ariation in correlation between per cent drops and yield from 

 year to year was large. Low and moderate positive correlation coeffi- 

 cients were found with Mcintosh in some years. With Northern Spy 

 the correlation was most frequently negative. Significant correla- 

 tions were not restricted to heavy-yield years. 



Variation within seasons, individual trees, date of harvest, and 

 undetermined factors render the correlation coefficients of per cent 

 drop versus yield of little or no value in estimating the number of 

 bushels of fruit dropped in a given orchard. Correlation between 

 weight of drops and yield, and its regression equation, gave a better 

 picture of effect of yield on drop. 



Very high correlations were found between total weight of drops 

 and yield over a period of years. 



Although certain thinned trees dropped less fruit than unthinned 

 trees, with others the reverse was true. Thus for all trees the differ- 

 ence in drops due to treatment was not statistically significant. 



Dropping was retarded when trees were sprayed with borax. 



