26 CIRCULAR 867, U. S. DEPARTMENT OF AGRICULTURE 



tative tissues, it was considered promising as a thinning agent. Con- 

 ceivably, such a treatment, when properly timed, might reduce set 

 by coating over the stigmatic surfaces and thus prevent either further 

 pollination or pollen germination. In a later paper Stebbins, Neal. 

 and Gardner (4,1) presented results on the use of three oil-wax 

 formulations for thinning Wealthy, Mcintosh, and Duchess apples. 

 In this experiment the treatments had no significant effect on fruit 

 set, and the authors concluded that these oil-wax emulsions used 

 alone at a concentration of 1 gallon per 100 gallons of spray did not 

 result in sufficient thinning to warrant their use for this purpose. 



Ken worthy (26) observed a thinning effect on Delicious following 

 the use of postbloom sprays of a mixture of polyethylene polysulfide 

 (p. e. p. s.) and zinc dimethyl dithiocarbamate-cyclohexylamine com- 

 plex (Zimate). This mixture was being tested for scab control. No 

 reduction in fruit set occurred when these materials were used sepa- 

 rately. The following year this spray mixture was used on Stayman 

 11 days after full bloom, for the purpose of thinning. The polyethyl- 

 ene polysulfide was used at the rate of 2 pounds per 100 gallons in 

 all sprays and the Zimate at one-eighth and one-fourth pounds per 

 100 gallons. Prior to the June drop the checks showed 77.6 percent 

 set. the one-eighth pound of the Zimate 17.3 percent set, and the one- 

 fourth pound dosage 27.2 percent set. At harvesttime the trees re- 

 ceiving the one-fourth pound of Zimate bore 16.6 fruits per 100 blos- 

 soming spurs, while the difference in set between the one-eighth 

 pound application and checks had disappeared, being 35.8 and 35.1 

 fruits per 100 blossoming spurs, respectively. In addition to showing 

 promise as a postbloom thinner for apples. Kenworthy also reported 

 that preliminary observations over a 2-year period'indicated that this 

 spray may reduce fruit set on peaches when applied near the shuck- 

 fall stage. 



Flory and Moore (12) used the p. e. p. s. — Zimate spray mixture 

 for the thinning of York Imperial. The concentration was 2 pounds 

 of polyethylene polysulfide plus 1 pound of Zimate per 100 gallons. 

 The treatments employed were (1) one spray 10 days after full 

 bloom, (2) two sprays 10 and 20 days following full bloom, and 

 (3) 3 sprays 10, 20. and 30 days following full bloom. The number 

 of fruits set per 100 blossoming spurs were as follows : Checks. 31 : 

 1 spray. 11: 2 sprays. 20: and 3 sprays, 12. In a test on Stayman 

 similar results were observed, but less thinning occurred on this 

 variety than from comparable treatments on York Imperial. 



A spray containing 2 pounds of polyethylene polysulfide and one- 

 fourth pound of Zimate per 100 gallons as used at the calyx stage 

 on Rome Beauty apples and at the shuck stage on Elberta peaches 

 by Southwick, Hoffman, and Edgerton {39). The treatment failed 

 to reduce appreciably the set of either of these fruits. However, in 

 the Rome Beauty experiment where conditions were not favorable 

 for chemical thinning, both a dinitro bloom spray and a calyx spray 

 of the sodium salt of naphthaleneacetic acid seriously overthinned 

 the crop. 



Experiments in central "Washington performed by Batjer and 

 Thompson (J), involving the use of the polyethylene polysulfide and 

 Zimate spray, failed to result in fruit-set reduction on TTinesap and 



