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apple varieties reported thus far to be appreciably affected by 2,4-D 

 sprays are Winesap, Stayman Winesap, Kendall, and Bonum, the last 

 two being minor varieties. Apparently the differential effect of 2,4-D 

 on different species of plants, which is the basis of its usefulness as an 

 herbicide, extends even to varieties. 



Those workers interested in attempting to explain the differential 

 herbicidal eflect of 2,4-D might well ponder the results of Edgerton and 

 Hoffman (14), who introduced a solution of this compound into the 

 transpiration stream of Mcintosh apple trees. Numerous attempts to 

 control fruit drop of Mcintosh variety by 2,4-D sprays have been 

 uniformly unsuccessful, but a very definite effect was secured by the 

 injection method. Although abscission of both fruit and leaves was de- 

 layed, no injury to the trees was reported. 



While sprays of 2,4-D are effective in controlling drop of a few 

 varieties, its use is not without hazard in apple and pear orchards. For 

 best results it should be applied earlier than NAA; but the earlier it is 

 applied the more danger there is of damaging holdover effects which may 

 be expressed in deformed leaves and shoots the next spring. Marsh and 

 Taylor (27) described some severe damage to susceptible varieties of 

 apple from 2,4-D residue in a central spray system which had been 

 utilized for weed control and subsequently used for a late spraying 

 of the trees with summer oil. The persistence of the effect of 2,4-D is 

 sometimes remarkable. Moon, Regeimbal, and Harley (32) reported 

 a case in which Stayman Winesap, sprayed in August, 1946, showed 

 appreciable drop control in the following year's crop picked in October, 

 1947. 



Citrus Fruits. — Preharvest drop of oranges and grapefruit, unlike that 

 of apples and pears which in general occurs during the few weeks prior 

 to time of picking maturity, may straggle along for many weeks. This 

 situation is due in part to the fact that citrus, not being a starchy fruit, 

 has no definite physiological maturity stage. Once ripe enough to eat, 

 its picking may be, and usually is, delayed for weeks or even months 

 in order to catch a favorable market. Thus the cumulative loss from 

 droppage may be appreciable, rarely amounting to less than 10 per cent 

 of the crop and often much more. Certain varieties, such as Pineapple 

 and Temple oranges, may also exhibit a wave of heavy droppage in the 

 latter part of their season, in which most of the fruit drops within a few 



