THE McINTOSH DROP 17 



sideration for reasons discussed elsewhere in this bulletin. However, this new 

 development is in the experimental stage. Further investigations and trials 

 should give a more complete understanding of its possibilities. The best tech- 

 niques of application, the most economically effective ranges of dilution, the 

 proper utilization of proprietary substances, the ultimate effects on the tree and 

 on the fruit, the dependability of the method under variable environmental con- 

 ditions, the particular conditions, from an economic standpoint, warranting the 

 extra expense, and many other considerations are all yet to be fully developed. 

 Trials by growers are recommended and either the pure chemicals or commercial 

 preparations should be satisfactory. 



Summary and Conclusions 



The dropping of Mcintosh apples just prior to and during the usual harvest 

 period is a definite fault of the variety and is recognized as a serious problem 

 among commercial growers. Many other varieties have the same fault in greater 

 or lesser degree. 



The severity of the problem has brought about certain practices designed to 

 decrease losses. Spot picking and sun coloring have been utilized with variable 

 degrees of success. 



A reasonable continued growth of Mcintosh apples gives increased yields and 

 better fruit condition and emphasizes the practical value of a delayed fruit drop. 



The abscission process is characterized by a chemical dissolution of cell walls 

 and separation of tissues rather than by cell division as in abscission of blossoms 

 and young fruits. 



The significance of the nitrogen relationship is evident from several angles. 

 Dropping was more severe under cultural conditions which made nitrates plenti- 

 fully available, particularly late in the season. Heavy mulching, organic or min- 

 eral nitrogen applications, late cultivation, and limb injections of nitrogen tended 

 to increase the percentage drop of fruit. On the other hand, a low level of fertility, 

 sod culture, limited cultivation, low tree vigor, and late summer girdling tended 

 to delay the initiation of abscission processes. In many cases, dropping was found 

 to increase with increasing yields. Larger crops in well-fertilized orchards often 

 more than compensate for the heavier drop. 



In a planting of Mcintosh on clonal stocks, severity of drop seemed to be 

 related to the different stocks but not necessarily according to their vigor. 



Seed number was positively correlated with date of drop of apples from in- 

 dividual trees in three years. Number of seeds per apple and mean drop dates 

 varied among the different trees, but seed influence was practically always mani- 

 fest; and on any particular tree, the apples with many seeds tended to hang longer 

 than those with fewer seeds. 



Length of stems of apples was not an important factor in determining the time 

 of drop of Mcintosh. 



No clear indication was found of any relationship between mineral content 

 and preharvest drop. 



The effect of strain is not settled. It is probable that certain strains do not 

 drop as badly as others. There is some indication, however, that the dropping 

 tendency is not necessarily associated with a particular type of fruit color. 



The importance of weather conditions was evident but the proper evaluation 

 of all of the various factors was not possible. There was evidence of the signi- 



