16 MASS. EXPERIMENT STATION BULLETIN 372 



Influence of Spot Picking 



The place of spot picking should be mentioned at this point. Many growers 

 in Massachusetts are using this harvesting scheme and report much less loss 

 from dropping as well as a marked increase in color of the crop as a whole. Fruit 

 maturity is a factor in apple abscission. But further than this, there is some 

 indication that a partial harvesting of a crop results in a better chance for the 

 remainder to "stick on." On the other hand, many of the apples which are left 

 after a spot picking probably would not have dropped much sooner without the 

 stimulus of partial crop removal. Be that as it ma}', harvesting Mcintosh two or 

 three times according to color development is a sensible procedure, provided the 

 picking cost per bushel is not raised unduly. 



Influence of Chemicals 



The effectiveness of several chemical compounds in delaying and preventing 

 harvest drop of apples has recently been demonstrated. Following the discovery 

 that abscission of floral structures, stems, and petioles was delayed on cuttings 

 treated with certain hormone compounds, Gardner and others (5) conceived the 

 idea of utilizing these substances to prevent the normal dropping of fruits just 

 prior to and during the harvest period. They found that many of the commercial 

 so-called plant growth substances have some effect in delaying abscission. Naph- 

 thalenacetic acid and naphthaleneacetamide proved to be more effective than 

 certain esters or the indole compounds. Further experimental results have 

 checked and extended the original findings (6, 6a). The chemicals, applied 

 thoroughly in dilute sprays (1 to 10 parts per million of water) evidently delay the 

 abscission processes for periods varying from one to three weeks depending on 

 the variety and certain other factors such as temperature. Gardner reported 

 marked response to hormone sprays with more than twenty varieties including 

 Mcintosh. In contrast with other varieties the effect of the sprays on Mcintosh 

 was of rather short duration, usually 8 or 9 da^'s. First appreciable effects were 

 noted 24 to 48 hours after application. Concentrations as low as .0001 percent 

 (1 part per million) were effective, although the higher concentrations up to 

 .001 percent gave better control of dropping. Preliminary experiments (1939) 

 in the Experiment Station orchards at Massachusetts State College with a 

 .00025 percent solution of alpha naphthylacetamide gave positive results in one 

 Mcintosh block, but inconsistent results in another block. McCown and Burk- 

 holder (18) obtained no significant effect of a spray containing .0001 percent of a 

 naphthalene acetic acid with three varieties. Murneek (22) reported good results 

 with .0005 and .001 percent sprays of both substances. 



Gardner (6) found that best results followed the application of sprays to the 

 region of the abscission zone. Spraying the calyx end of Delicious resulted in 

 some delay of drop but application to the zone of attachment of stem and spur 

 was far more efifective. Since fruits not hit by the spray probably are not in- 

 fluenced, the necessity for thorough, drenching sprays is evident. Leaf coverage 

 was not found to be particularly important. After the effect wears off, fruit drop 

 may be sudden and severe. However, an additional spray or sprays will extend 

 the effective period. Repeated sprays at short intervals have been known to 

 cause such tight "sticking" that picking became a laborious task. 



The usefulness of hormone sprays in certain circumstances is unquestioned. 

 With Mcintosh, this method of drop control should be given particular con- 



