42 MASS. EXPERIMENT STATION BULLETIN 315 



59.12. These trees were very large and required from lj^ to 2J^ pounds of dust 

 per tree for satisfactory coverage. It is apparent that a pyrethrum dust con- 

 taining .2 to .3 percent pyrethrins gives better control than a derris dust con- 

 taining .5 percent rotenone, but their practical and economical value is not yet 

 determined. 



Control of Squash Vine Borer with Oils, Soap, and Nicotine. In field experiments 

 where the borer infestation in unsprayed Hubbard squash was 2.25 tunnels per 

 vine, oil emulsions diluted to contain 2 percent oil failed to give satisfactory con- 

 trol and caused slight injury to the vines. Lead arsenate and nicotine sulfate 

 combined with soap and pine tar soap (1 pound in 10 gallons of water) gave only 

 moderate protection. A spray consisting of 1 percent white lubricating oil emul- 

 sion and 40 per cent nicotine sulfate 1-500 was most effective, showing 26 percent 

 more reduction of borer than the standard treatment of 40 percent nicotine sul- 

 fate 1-250. This formula costs Y2 cent per gallon less than the standard spray 

 and promises to develop a practical value. 



Control of Cabbage Maggot with Calomel Dust. When 4 percent calomel-lime 

 dust was applied to 14 plats so that all possible combinations from 4 applications 

 were made beginning May 7 when first eggs were found and continuing at weekly 

 intervals, a single application at any of the treatment periods was not effective. 

 Applications at the first and second intervals gave 82 percent commercial control 

 of maggots and 88 percent large or medium heads. In general, two or more 

 treatments which included the first and second applications were satisfactory 

 but others were not. Of the untreated plants, 84 percent suffered moderate or 

 severe injury, although 43 percent reached satisfactory size. Corrosive sub- 

 limate solution 1-1000 continued to prove its superiority and if applied when the 

 eggs were first found yielded 80 percent commercially clean plants and 82 percent 

 satisfactory heads. Three applications of naphthalene flakes were equally effective. 



Applications of similar materials to radishes were less effective and although 

 two applications of corrosive sublimate solution gave moderate control the plants 

 were stunted by the treatment. 



Control of Onion Thrips. (A. I. Bourne.) Thrips were late in appearing this 

 past season and were much less abundant than for several years. There were few 

 fields in the Valley that showed any appreciable injury by these insects, although 

 the hot weather and long period of drought in midsummer offered conditions very 

 favorable for thrips. In the experimental plots the average number of thrips 

 per plant did not reach 20 until July 16. Their numbers reached the peak of 

 abundance July 30 to August 1 and dropped rapidly from that point. Set onions 

 did not show a heavy infestation, so that as they matured the migration of thrips 

 to seed onions was not serious. This condition was unusual in a summer so hot 

 and dry as that of 1934. 



None of the sprays or dusts used in the field tests gave as high a degree of 

 control as did the nicotine sulfate-soap combination, although rotenone sprays 

 (Ku-ba-tox) proved nearly as effective and appeared to have a considerable 

 residual effect which prevented rapid reinfestation. Grandpa's Wonder Pine 

 Tar soap proved fully as efficient a spreading and wetting agent as fish oil soap, 

 although its cost is higher. Rotenone dusts and a pyrethrum dust did not give as 

 good control as sprays, due chiefly to the mechanical difficulties in forcing a dust 

 into the tight axils of the inner leaves where most of the thrips are located. A 

 combined spray of nicotine sulfate and wettable sulfur gave only moderate con- 

 trol, the sulfur proving inferior to soaps as a spreader and distributing agent. 



Because of the mechanical difficulties involved in applying insecticides for the 



