FRUIT THINNING WITH CHEMICAL SPRAYS 23 



cross-pollination. This is indicated by the data in table 6 for the 

 variety Delicious (orchards 1 and 2), New York (22, 39), for the 

 years 1946 and 1947. These two orchards located on neighboring 

 farms were similar with respect to soil, age of trees, culture, and 

 provisions for cross-pollination. The season of 1946 was character- 

 ized by good weather for cross-pollination throughout the bloom 

 period, while in 1947 a general rain lasting about 30 hours occurred 

 at the peak of bloom. Although the check trees set somewhat heavier 

 in 1947 than in 1946, a calyx application of the sodium salt of naph- 

 thaleneacetic acid at 10 p. p. m. resulted in greater thinning in 1947 

 than in 1946; the percentage of thinning amounted to 73 and 55, 

 respectively. 



The fruit-set data in table 6 for Delicious and Winesap under 

 Washington conditions sIioay that naphthaleiieacetic acid applied at 

 the same stage of development reduced set considerably more in 1948 

 than in 1946. The bloom season of 1948 in central Washington was 

 characterized by relatively cool weather and occasional heavy 

 showers, which probably interfered with the normal amount of cross- 

 pollination of these two self -unfruitful varieties. 



In Washington there is usually greater variability in results (par- 

 ticularly on W^inesap and Delicious) when naphthaleiieacetic acid is 

 used as compared with the dinitro materials. Thus in seasons favor- 

 able for fruit set naphthaleneacetic acid generally is not so effective 

 as the dinitro materials, while in seasons when adverse conditions exist 

 for fruit set there seems to be a greater likelihood of overthinning 

 with this material. In Washington, Golden Delicious and Jonathan 

 under most conditions can be sprayed with naphthaleiieacetic acid 

 with little danger of overthinning or foliage injury, although gen- 

 erally the dinitro sprays are considered preferable for use on these 

 varieties. 



When conditions for crOss-pollination are uniform, trees on im- 

 perfectly drained soil seldom set as heavily as trees growing on deep 

 well-drained soil. This is especially pronounced in wet springs when 

 anaerobic soil conditions prevent the early growth of new rootlets. 

 Under such conditions a naphthaleneacetic acid spray may seriously 

 overthin the crop, even though untreated trees set too heavily for 

 good commercial size. In table 6 fruit-set records are given for two 

 New York Baldwin orchards, in which thinning experiments were 

 conducted in 1947 {39). Orchard 1 was located on well-drained land. 

 Although the set of the check trees was not excessive, both treat- 

 ments (10 p. p. m. at full bloom and 20 p. p. m. at calyx) proved 

 worth while from the standpoint of producing fruit of good commer- 

 cial size. In orchard 2, where the soil was waterlogged for a period 

 of several weeks during the early part of the growing season, a calyx 

 spray of 20 p. p. m. severely overthinned the crop. Under these condi- 

 tions the naphthaleneacetic acid treatment at calyx was more drastic 

 in its thinning effect than dinitro sprays applied during full bloom. 

 Similar results were obtained with Delicious in orchard 3 (39 and 

 table 6), growing on imperfectly drained soil. In this instance a 

 calyx spray of naphthaleneacetic acid at 10 p. p. m. practically de- 

 fruited Delicious. These results are in contrast to those obtained the 

 same season in orchard 2 (39) where the soil was well-drained and 



