ANNUAL REPORT, 1947-48 39 



Following very thorough application to relatively small plants, all the sprays 

 gave excellent initial kill: Black Leaf 40, Ryanex, and DDT, 99 percent control; 

 Derris and DDD, 95 percent or over. After 7 days, the Derris, DDT, and DDD 

 plots showed no increase in thrips population; Black Leaf 40 and Ryanex, how- 

 ever, did not give prolonged protection. 



Of the dusts, DDT and BHC (benzene hexachloride) gave practically complete 

 control following heavy application, and only slight increase in thrips population 

 after a 7-day interval. Plants dusted with BHC retained a pronounced odor 

 for weeks, but the onions when harvested did not have their flavor impaired. 

 Ryanex dust gave approximately 94 percent control. 



Control of Cabbage Maggot. (W. D. Whitcomb, W. J. Garland, and C. S. 

 Hood, Waltham.) The natural infestation of the cabbage maggot in the experi- 

 mental planting at Waltham caused 79 percent commercial injury in 1947. In 

 the same planting, one and two applications at 10-day intervals of benzene 

 hexachloride-talc dust at the rate of 25-30 pounds per acre gave perfect control. 

 The most effective dusts contained 5 and 3 percent benzene hexachloride, but 

 dust containing 1 percent benzene hexachloride was commercially satisfactory. 



Benzene hexachloride harrowed into the soil at the rate of 2 pounds per acre 

 before transplanting failed to give satisfactory protection.. 



The treatments which gave excellent control produced 85 to 95 percent market- 

 able heads, and there was no taste or odor contamination at harvest. Although 

 no records were obtained, observations indicated that the cutworm injury was 

 completely eliminated by these treatments. 



Studies of Odor and Taste Contamination from Soil Treatment witli Benzene 

 Hexachloride. (W. D. Whitcomb, W. J. Garland, and C. S. Hood, Waltham.) 



Benzene* hexachloride is an effective insecticide for the control of wireworms 

 and cabbage maggot. However, it has a strong, persistent musty odor and 

 taste which may be imparted to vegetables grown in treated soil. 



In the experimental garden where areas were treated with benzene hexachloride 

 at the rate of 2, 3, and 5 pounds per acre, carrots, onions, parsnips, and radishes 

 were judged free from odor or taste contamination at the harvest by fifteen 

 disinterested testers. Potatoes were contaminated at all dosages, and beets at 

 the higher rates of application. 



In general, the odor and taste of BHC were accentuated by boiling and baking. 

 Potatoes still retained the odor to an undesirable degree seven months after har- 

 vest. Radishes and turnips were contaminated when the benzene hexachloride 

 was applied as a dust to the plants after the shoulder was developed above ground. 



Control of Squash Vine Borer. (W. D. Whitcomtr, W. J. Garland, Waltham.) 

 The natural infestation by the squash vine borer in the experimental plantings 

 at Waltham in 1947 was 49.5 borers per vine. Applications of dust gave ap- 

 preciable protection when applied at weekly intervals during July. 



The most effective treatment was dusting with 3 percent DDD (Rhothane) 

 which gave 81.6 percent protection. Other dusts which gave satisfactory pro- 

 tection were effective in the following order: 5 percent methoxy DDT; 0.5 per- 

 cent DDT plus 0.06 percent pyrethrins; and 40 percent ryania powder. 



The infestation in both the untreated and the dusted plants was about 30 

 percent greater in Cucurbita maxima plants than in C. pepo. 



Biology and Control of Common Red Spider on Greenhouse Plants. (W. D. 



Whitcomb, W. J. Garland, and C. S. Hood, Waltham.) Parathion, a new 

 organic phosphate insecticide, was found to be very effective for control of the 



