10 MASS. EXPERIMENT STATION BULLETIN 372 



other materials also increased early dropping, especially when injected in sufficient 

 quantity or concentration to cause visible foliage injury. 



Other corroborative evidence can be found in the practical experiences of fruit 

 growers who often report increased drop under conditions of high fertility, es- 

 pecially in relation to nitrogen. On the other hand, less concern with drop is 

 manifest by those growers who operate their orchards on the "hard" side in 

 contrast to being liberal with nitrogen. Scantily fed orchards in tough sod usually 

 show less dropping — and less yield — than orchards in sod highly fertilized, 

 under regular cultivation, or under heavy mulch. 



Effect of Girdling 



In the summer of 1939, a 15-year-old tree was chosen for a study of the dropping 

 behavior of individual limbs treated in different ways. This tree was carrying 

 a heavy crop and was in a fair state of vigor. Branch treatments and subsequent 

 dropping results are given in Table 5. 



Table 5 — Effect of Limb Treatments on Subsequent Dropping (1939) 



Total Percent of Apples 



Treatment Date of Number Still Hanging 



Treatment of Apples After October 4 



1. Girdled by 3 knife cuts Sept. 7 54 43 



2. Girdled by removing strip of bark Sept. 7 50 39 



3. Xylem partly destroyed by boring Sept. 7 46 37 



4. Girdled by removing strip of bark Aug. 1 157 25 



5. Check 600 19 



All of the treatments had a retarding influence on fruit drop. Girdling was more 

 effective when done in September than a month earlier, even though the August 

 girdle did not heal over. It should be pointed out here that such treatments, 

 though useful from an experimental standpoint, are drastic and of course im- 

 practical. Murneek (21, 22) has shown that apple fruit set can be increased by 

 branch ringing and evidently the effect is produced largely by the alteration of the 

 carbohydrate supplies. The girdling was done at the time of full bloom. Hodgson 

 (9) found that girdling reduced fruit drop in the persimmon. He observed that 

 excessive dropping was usually associated with high tree vigor. 



The single-year data in Table 5 are rather limited but the differences in the 

 drop of the variously treated branches are quite pronounced. It would seem 

 that girdling should reduce the upward passage of nitrogen and other nutrients 

 as well as the downward movement of carbohydrates. Perhaps both of these 

 effects could influence the normal initiation and progress of fruit abscission. 

 With the role of nitrogen in its relation to drop more or less evaluated (above), 

 it would seem that nitrogen supply is probably the important factor. 



Effect of Stock 



Block D is a 10-year-old clonal stock planting of Mcintosh and Wealthy ' 

 Table 6 gives the yield and drop data for some of the Mcintosh trees for the 

 period 1934-1937 inclusive. 



