16 BULLETIN 1406, U. S. DEPARTMENT OF AGRICULTURE 



particularly with the Baldwin, there was medium to bad dropping- 

 at the time the fruit was rated in optimum picking condition. 



From the data available it has been impossible to determine the 

 exact causes leading to the loosening of the fruit and dropping 

 from the tree. It is apparent from the data presented in Table 3 

 that under certain conditions the fruit will drop when still hard, 

 whereas under others it will continue to adhere to the tree until 

 fairly soft, Jonathan, for example, showed only slight dropping 

 at Wenatchee in 1924, when it was testing only 15.4 pounds, but 

 showed medium dropping at Council Bluffs the same year when 

 testing 18 pounds. In many instances fruit of a greener ground 

 color in one section would show more dropping than fruit with a 

 more yellow ground color in another district, It has not been 

 possible to correlate dropping in any very satisfactory manner 

 either with the prevailing temperatures or with rainfall or irriga- 

 tion. In the varieties here studied it does not appear to be very 

 definitely correlated either with the firmness of the flesh, the ground 

 color of the fruit, or the length of time the seeds have been brown. 



In the Baldwin, Delicious, Grimes Golden, and Jonathan the 

 loosening and dropping of the fruit seems to be associated to a 

 certain extent with the number of days that have elapsed following 

 blooming. Baldwin generally showed some dropping in from 135 

 to 145 days following blooming. Delicious showed dropping in 

 135 to 140 days following the date of full bloom. Grimes Golden 

 generally ran 140 to 150 days, with Jonathan 135 to 150 days. 



On the other hand, Winesap and Ben Davis showed slight drop- 

 ping after about 150 days in Massachusetts and 160 to 170 days in 

 districts having long growing seasons. It should be pointed out that 

 even 150 days in the former district carried the fruit into late Octo- 

 ber, when cold weather and heavy frosts are likely to occur. It 

 would appear that Winesap and Ben Davis really require from 160 

 to 170 days to reach natural maturity on the tree, but if the season 

 is shorter than this, loosening and some dropping may occur as cold 

 weather comes on. 



Particular conditions in the trees and in the orchard also undoubt- 

 edly exert a great influence on the way the fruit adheres to the tree. 

 At Wooster, in 1924, for example, the fruit of all varieties grew very 

 rapidly, attained large size, and adhered remarkably well. A me- 

 dium-sized crop on vigorous nitrated trees with ample soil moisture 

 in this case resulted in the fruit holding on the tree until late in 

 the season. 



It has been shown that so long as it adheres to the tree growth 

 of the fruit is generally occurring, indicating that the fruit is actively 

 receiving food materials. It seems probable that when the move- 

 ment of food materials from the tree to the fruit stops for any 

 reason the abscission layer forms and the fruit loosens or drops from 

 the tree. It is apparent from the data here presented, however, 

 that any explanation of the real factors involved in the dropping of 

 fruit will have to be based on studies of conditions within the in- 

 dividual tree rather than the external or climatic conditions pre- 

 vailing. 



Since it is absolutely essential that the crop be picked before drop- 

 ping becomes excessive, the way the fruit adheres to the tree is of 



