Preharvest Apple Drop with Special 

 Reference to Mcintosh 



By L. P. Latimer, Assistant Horticulturist 



McIXTOSH APPLE TREES have the bad habit of frequently 

 dropping a considerable proportion of their fruit before the de- 

 sired amount of red color has d'eveloped. Red color is an important 

 requirement for "Fancy" and "A" grade Mcintosh. Under-colored 

 fruit, although sound and free from blemish, must be sold as "B" 

 grade. 



MacDaniels^^ found that dropping was preceded by the forma- 

 tion of an abscission layer across the pedicel of the fruit. Dickerson'*, 

 MacDaniels^^^ and Southwick^-'' have suggested that a reduced ni- 

 trogen supply in the soil results in fewer drops and better color than 

 when nitrogen is abundant. 



Spot-picking has been suggested as a means of preventing serious 

 loss by the pre-harvest drop. This method of harvesting apples, 

 however, involves greater expense. Therefore, there has long been 

 a desire for a method of preventing dropping before all the fruit has 

 developed sufficient color for commercial purposes. For this reason, 

 in 1938, an investigation was begun to determine the factor, or fac- 

 tors, responsible for the pre-harvest drop. It should be noted par- 

 ticularly that this work was begun before Gardner ct. al/> had re- 

 ported the beneficial effect of growth-promoting substances in re- 

 ducing the pre-harvest drop of certain apple varieties. 



For several years previous to the initiation of this project, rec- 

 ords were kept on the proportion of dropped fruit in the Experiment 

 Station orchard at Durham, New Hampshire. Data obtained from 

 1932 to 1937 on the per cent drop of fruit from 50 eighteen-year-old 

 trees located in the section of the orchard known as the BFP block 

 were subjected to analysis of variance. The results showed that cer- 

 tain trees dropped a significantly greater per cent of fruit annually 

 than others in the same block. There seemed to be a tendency for 

 the lighter-dropping trees to be more or less grouped together. The 

 same is also true for heavy-dropping trees. 



It was thought first that differences in the rate of dropping might 

 have been caused by rootstock differences. If this were the case, 

 heavy-and light-dropping trees could hardly be expected to be segre- 

 gated into groups as these were. Therefore, it was assumed as more 

 probable that soil differences, either physical or chemical, might be 

 the cause of the differences in amount of fruit-dropping in the differ- 

 ent areas of the BFP block. 



EFFECT OF SOIL 



The eight trees in the block identified as BFP which dropped 

 the greatest and the eight which dropped the least percentage of fruit 

 annually were used in this investigation. The difference in per cent 



