FRUIT THINNING WITH CHEMICAL SPRAYS 25 



ginia show that one application of either of these materials failed to 

 prevent completely fruit set on York Imperial, Golden Delicious, 

 Jonathan, and Yellow Newtown. Almost complete defruiting was 

 obtained on Winesap, Delicious, Grimes Golden, and Gano ; Stayman 

 was intermediate. 



Magness and Batjer (30) reported later that all the trees sprayed 

 in these initial experiments on which the set of fruit was reduced to 

 not more than 1 fruit per 10 blossom clusters on heavily blooming- 

 trees formed fruit buds and set good crops the year following treat- 

 ment, During a second season's work substantially the same results 

 were obtained on York Imperial, Stayman, and Gano. The data in- 

 dicated that TOD at 0.8 percent concentration, thoroughly applied, 

 was sufficient to prevent the set of a large proportion of the bloom 

 of all varieties investigated, with the possible exception of Yellow 

 Transparent. DNO, an insecticide preparation, at one-half dormant 

 strength (1 percent) appeared to be slightly more effective than TOD 

 at 0.8 percent in preventing set. The delayed cluster bud or early 

 pink stage was found to be the most satisfactory stage for reducing 

 fruit set. There were indications that later sprays of these materials 

 might result in sufficient injury to prevent fruit-bud formation. 

 These treatments killed all young foliage as well as blossom buds that 

 were effectively hit. All of the blossoms and leaves were killed on 

 many spurs and some of the weaker spurs failed to make any further 

 growth, giving the immediate appearance of very serious injury. In 

 most cases, however, the leaf bud in flower clusters was not injured, 

 and as a result of a reduced fruit set and conservation of reserve foods 

 greater foliage growth was produced by sprayed trees than by un- 

 sprayed trees in advance of the period of fruit-bud formation. 



Childs and Brown (7) used TOD sprays on Yellow Newtown in 

 Oregon, employing a method termed "spot spraying." The applica- 

 tions were made when approximately 10 percent of the bloom was 

 open. Since the Yellow Newtown is a distinct biennial bearer, the 

 idea of spot spraying was to reduce fruit set sufficiently on a certain 

 part of the bearing area so that in succeeding years each tree would 

 produce some bloom each season. The data indicate that this was 

 accomplished. Since annual hand thinning was still required for good 

 commercial size and quality on that part of the tree bearing fruit, 

 this approach would not seem to materially affect the total amount of 

 hand thinning over a period of years. However, the changed tree 

 performance would permit a much better distribution of the required 

 man-hours for thinning from year to year and conceivably result 

 in a better net return to the grower. Following the work of Childs 

 and Brown the tar oil distillate spray for reducing fruit set probably 

 reached its greatest commercial use on the Yellow Newtown variety 

 in the Hood River Valley of Oregon. Because of its severe caustic 

 properties it is not adapted for use as an annual thinning treatment. 



Gardner (13) reported that sprays of an oil- wax emulsion at 1 and 

 5 percent concentrations applied on mature Duchess trees when in 

 full bloom reduced the set of fruit. The results from the two con- 

 centrations were almost identical. The reduction in set was not drastic 

 but sufficient to reduce substantially the amount of hand thinning 

 required. As this oil-wax emulsion appeared nontoxic to all vege- 



