FRUIT THINNING WITH CHEMICAL SPRAYS 29 



to take place. Thus, in the season following the "on year" there is 

 a reduced bloom resulting in a short crop. Under these conditions 

 excessive fruit-bud formation takes place. Once such a fruiting 

 habit is established alternate years of heavy bloom and heavy crop 

 are followed by relatively light bloom and light crop. Under many 

 conditions practically all varieties show a tendency toward alternate 

 bearing, although this characteristic is much more pronounced with 

 certain varieties than others. Even with varieties considered regular 

 in their bearing habits, very early thinning is often necessary if the 

 tendency toward alternation is to be kept at a minimum. With bien- 

 nial varieties, under most conditions it is not feasible to hand-thin 

 early enough to avoid pronounced alternation. 



Perhaps one of the most outstanding features of chemical thinning 

 sprays is their effect on alternate bearing. These sprays, particularly 

 the dinitro chemicals, reduce fruit set in the blossom stage, thus 

 eliminating many fruits at the earliest possible time. Thinning in the 

 bloom stage avoids wastage of carbohydrates, thereby enabling the 

 tree to form a greater number of fruit buds for next year's crop. 

 The data in table 8 illustrate this point. Increase in yield as a result 

 of chemical thinning varied from 23 to 66 percent. The check trees 

 of the Wealthy variety without benefit of hand thinning were com- 

 pletely biennial, as may be noted from the absence of crop the second 

 and fourth year of the experiment. With both Golden Delicious 

 and Wealthy the chemically thinned trees produced sufficient bloom 

 each year to necessitate chemical thinning. 



Yield records of commercial orchards using chemical thinning 

 sprays over a period of 2 or more years often show an increase of 

 15 to 20 percent over hand-thinned or non thinned fruits. In orchards 

 or blocks of trees that were decidedly biennial, chemical thinning fre- 

 quently resulted in a more substantial increase. 



Reduction in Thinning Cost 



In some fruit areas chemical thinning has been used with the ob- 

 jective of eliminating the need for hand thinning entirely. How 

 successfully this can be accomplished will depend upon a variety of 

 factors that have been discussed previously. In many instances use 

 of chemical thinning sprays do not result in sufficient reduction in 

 fruit set. In central Washington heavy thinning is required for 

 satisfactory annual crops of good size and quality. In this section 

 chemical thinning generally results in accomplishing one-half to 

 three-fourths the thinning necessary. It is common for fruit growers 

 in certain years to do all their thinning with sprays. 



In some instances the amount of fruit on sprayed trees following 

 the June drop may appear as great as on similar trees not sprayed. 

 In such cases the unsprayed trees seem to have a much greater initial 

 fruit set but may "shed down" to a point following the June drop 

 where both sprayed and unsprayed trees have about the same ultimate 

 set, In several experiments (5) fruit set following the June drop was 

 approximately the same on both sprayed and unsprayed trees ; never- 

 theless the amount of bloom the following years was appreciably 

 greater on the trees that had received the dinitro spray. Reduction 



