ANNUAL REPORT, 1937 65 



were abundant from July 2 to 15, and mature maggots were leaving the rolled 

 leaves from July 27 to August 10, A distinct third generation developed on 

 young trees from eggs laid August 20 to 25 and mature maggots were plentiful 

 September 7 to 14. It i= now definitely established that a third generation of this 

 midge develops in a normal season and that it can become very abundant on 

 young trees or wherever new growth is available. 



No new infestations outside the known infested area were discovered. 



Natural enemies, especialh' Triphleps insidiosa Say, were slightly more abun- 

 dant and active than in other years but failed to cause any noticeable reduction 

 of infested tips. 



Control studies were conducted on small trees partly interplanted among old 

 trees and partly in separate blocks. The susceptibility of the different varieties 

 in this orchard was determined by counting the maggots in the rolled leaves of 

 10 typical infested tips on June 12. The result is as follows: 



Variety 



Baldwin 



Mcintosh 



Starking 



Golden Delicious 



Experimental sprays were applied 5 times (May 25, 28, June 1, 4, 8) during the 

 oviposition period of the first generation, and again 5 times (July 6, 9, 13, 16, 20) 

 during the corresponding period of the second generation. Although some trees 

 received sprays at both periods, no trees received the same spray materials at 

 both periods. Records were taken by counting the number of infested tips and the 

 degree of injury on each sprayed tree and the number on the nearest unsprayed 

 tree of the same variety and corresponding size. 



In general, the protection resulting from spraying was disappointing and from 

 25 to 60 percent of the tips were infested on the sprayed trees, although only about 

 10 percent of the tips were moderately or severely infested. Less control was 

 obtained on Starking trees than on Mcintosh, Richared, or Golden Delicious. 

 Spraying for control of the first generation reduced the infested tips by 46 to 

 12 percent. Wettable cube powder containing 3.65 percent rotenone, used at the 

 rate of 6 pounds in 100 gallons, with the addition of 3 pounds of water soluble 

 diglycol stearate wax as a spreader and sticker, applied to Mcintosh and Richared 

 3-year-old trees was the most effective treatment. Nicotine sulfate and molasses, 

 nicotine sulfate with fish oil soap and karaya gum, and a nicotine bentonite wet- 

 table powder with a commercial spreader called Ultrawet gave moderate control. 

 Summer oil diluted to 1 percent plus fish oil soap failed completely. 



In the second generation experiments, nicotine sulfate 1-800 plus molasses 

 3 percent was the most effective, and reduced the infestation 48 percent on Golden 

 Delicious. The cube-wax mixture was again good and averaged the best for both 

 series. When nicotine sulfate 1-800 was added to the summer oil-fish oil soap 

 mixture which had failed previously, the control became good although the test 

 was inconclusive because of poor growth on the trees. 



A count of the maggots in 10 typical rolled leaves on sprayed trees during the 

 larval period of the second generation showed that the number was reduced in 

 proportion to the effectiveness of the spray in preventing infestation. 



Although valuable information regarding the effectiveness of insecticides has 

 been obtained, the only logical conclusion that can be drawn from this work is 

 that spraying alone is not a practical means of combating the apple leaf-curling 

 midge. 



