ANNUAL REPORT, 1935 43 



soap and bentonite sulfur. One application of these materials in addition to 

 the regular schedule was made July 1 by the owner. 



In the block sprayed with the soluble and insoluble nicotine compound, the 

 examination of 15,283 apples showed 6.31 percent stung and 2.64 percent 

 wormy; and in the block sprayed with the nicotine sulfate-sulfur soap combina- 

 tion 2.58 percent and 1.44 percent of the 5,265 apples were stung and wormy 

 respectively. However, only 0.40 percent and 0.33 percent of the harvested 

 apples were wormy, and this is considered excellent control. Most of the 

 worms were in the dropped fruit, there being 11.22 percent more stung and 

 wormy windfall apples in the block sprayed with the nicotine sulfate-sulfur 

 soap combination than in the block sprayed with the nicotine compound. Al- 

 though these figures favor the latter treatment, the differences are not suffi- 

 ciently conclusive to offset other factors such as fewer apples, more open trees 

 permitting better coverage, and the addition of bentonite sulfur to the nicotine 

 sulfate spray. 



Control of Onion Thrips. (A. L. Bourne. ) Conditions during late spring 

 and early summer were unfavorable for onion thrips. The insects were late in 

 appearing and their development was slow. At the peak of their seasonal 

 abundance their numbers were insignificant while the cool weather and frequent 

 rains stimulated the onion plants to make rapid growth, so that little or no 

 injury resulted. Unfortunately for the crop, these weather conditions favored 

 the development of blast, which first appeared about the third week of July 

 and developed rapidly, so that by early August it was present very generally 

 throughout the Valley, and in most of the fields the plants were dying down 

 rapidly. 



The most promising of the resistant varieties of onions in the tests of 1934 

 were selected for further study, and again consistently showed fewer thrips 

 per plant than did the Danvers Yellow Globe, the standard variety grown in 

 the Valley, although the differences were not so marked as in the previous year 

 because of the comparative scarcity of thrips. The average number of thrips 

 per plant is recorded in the following table. 



Average Number of Thrips 

 per Plant 



Date 



Danvers Winegar Harris Utah 



June 24 0.2 0.2 0.6 0.2 



July 1 0.8 0.7 0.6 1 



9 5.1 2 1.9 2.5 



15 13.6 6 8 6 



22 ,. 15.4* 4.5 6 5.6 



30 20. 8t 5 6.8 4.9 



August 5 5.5 7.2 6.6 10.4 



12 5.3 14.4 9.2 17.8 



19 % 29.6 % 30 : 7 



*Blast began to appear. 

 fPlants dying rapidly. 

 jPlants down. 



It should be noted that the three resistant varieties showed a very light in- 

 festation throughout the season. The rapid rise in thrips population on these 

 varieties occurred after blast had killed the plants of the Danvers variety and 

 the thrips had migrated into these plots. The Winegar plots located nearest 

 the Danvers received the greater part of this migration. 



