FRUIT THINNING WITH CHEMICAL SPRAYS 11 



ticularly if applied to trees of low vigor or when adverse weather 

 conditions prevail during the bloom period. 



Number of Spray Applications 



One application of an Elgetol spray is not usually sufficient to 

 approach the desired amount of thinning on some apple varieties 

 when grown under conditions conducive to a heavy fruit set. In the 

 Northwest Golden Delicious, Yellow Newtown, and Jonathan fre- 

 quently require two sprays. It is also desirable in some instances to 

 apply two sprays to Wealthy in the Northeast. This is especially true 

 for vigorous "on-year" trees that produce considerable lateral bloom 

 on the past season's terminal growth. This bloom opens several days 

 after the spur bloom, and a second application is required for ade- 

 quate thinning. Table 4 summarizes some of the results, comparing 

 the effectiveness of one and two applications of an Elgetol spray 

 applied to three varieties of apples. As might be expected in most of 

 the experiments, two sprays resulted in appreciably more thinning 

 than a single application. Overthinning resulted in two <>f the three 

 experiments (table 4) in New York with the Wealthy variety. In 

 those instances of overthinning following two sprays, the trees were 

 of relatively low vigor, caused in one case by a low nitrogen level and 

 in the other by imperfect soil drainage. 



In Washington the double Elgetol spray treatment overthinned 

 both Jonathan and Golden Delicious in 1948, while the same treat- 

 ment, though significantly reducing fruit set, failed to thin sufficiently 

 these varieties in other years. It is believed that weather conditions 

 in 1948 during the bloom period (cool and humid) caused a greater 

 indirect action of the spray. This point will be discussed in a subse- 

 quent section. 



Whether or not heavy -setting varieties will require two sprays to 

 approach the desired amount of thinning depends upon locality, tree 

 condition, and the type of weather prevailing during the bloom 

 period. Under Northwest conditions it is a general commercial prac- 

 tice during seasons of favorable weather to apply two sprays on 

 Golden Delicious, Yellow Newtown, and Jonathan. In this area Wine- 

 sap and Delicious under favorable conditions are sometimes sprayed 

 twice. Since conditions, particularly tree vigor and pollination, vary 

 from orchard to orchard it remains for individual fruit growers to 

 determine under their own particular conditions the advisability of 

 applying a second spray. When two sprays are used it is preferable 

 to apply the first one about 1 or 2 days ahead of full bloom, when 

 approximately 50 to 75 percent of the flowers are open. The second 

 application should be made from 1 to 3 days later when most of the 

 remaining flowers have opened. 



Pollination and Bee Activity 



As stated previously successful use of thinning sprays is predicated 

 on the assumption that fruit set will be heavy. Weather conditions 

 during the bloom season is an important factor in determining the 

 adequacy of pollinizers and number of bees needed to insure a heavy 



