12 MASS. EXPERIMENT STATION BULLETIN 381 



for best control, the hormone should come in contact with the abscission 

 zone itself. This is the area that roughly defines the location of the 

 abscission layer which, upon development, separates the pedicel from the 

 cluster base (the stem from the spur). Gardner, Marth, and Batjer (2) 

 have reported some eflFect from a spray applied only to the calyx end of 

 Delicious fruits. But such an eflfect must be of doubtful significance. 

 They also found that leaf coverage is not particularly important. Apples 

 only a short distance away from sprayed foliage seem to be aflfected little 

 if at all. 



The amount of spray material which is adequate for thorough coverage 

 depends on a number of factors such as wind movement, spray pressure, 

 and especially spraying technique. Material, of course, should be applied 

 efficiently with a minimum of wastage, but it is better for best control of 

 drop to apply too much than too little. Reports of amounts used in 1940 

 vary remarkably. In some cases, good results evidently were secured 

 with young trees when less than 5 gallons of spray were used per tree. 

 Another extreme was the application of more than 40 gallons on single 

 trees. These, of course, were very large trees bearing 15 to 40 bushels 

 of apples. Two ways of determining the amount of spray material needed 

 are based respectively on tree size and on tree crop. Competent men on 

 a spray rig will automatically consider both aspects. With hormone 

 spraying it is the apple rather than the leaf that deserves primary con- 

 sideration and this fact naturally places emphasis on the crop of fruit 

 rather than on the size of tree. On this basis, a recommended application 

 might be from one to two gallons of spray for each estimated bushel of 

 apples. Results have been too inconsistent and individual situations are 

 too variable to allow a more specific recommendation. The important 

 point is that very thorough coverage is essential. For example, in Mary- 

 land (1), with Delicious averaging seven bushels per tree, a 5-gallon 

 application per tree was just one-half as effective in retarding drop as a 

 10-gallon application of the same strength. 



This brings up the possible use of dust in a drop control program. 

 Several advantages of dusting over spraying are obvious to those who 

 have used both systems. One of the most important considerations is 

 the shorter time required for dusting. Since hormone spraying comes 

 during a particularly busy season, the time required to put on an applica- 

 tion is of vital concern to growers. Hence, the question of incorporating 

 the hormone in a dust carrier for use in the usual orchard dusters has 

 been raised. Although the efficacy of this method of hormone application 

 to fruit trees is practically unknown, it is believed that dusting will not 

 eflfect as thorough coverage as spraying. Intimate contact with tissue 

 .surface is better obtained with a wet than with a dry film of material. 

 The question is further complicated by the fact that, to be most effective, 

 the hormone probably should be in solution, although for certain other 

 uses dust application of hormones has been quite effective. The possibil- 

 ities of hormone dusts are being investigated further and it is possible 

 that certain of the obvious difficulties may be remedied, .^t the moment, 

 however, since spraying itself is none too effective, partly because of in- 

 adequate coverage, a dust program for drop control ofifers little encourage- 

 ment, especially with Mcintosh. 



