ANNUAL REPORT, 1945-46 35 



Orchard Tests Against Apple Pests.^ Because of the adverse weather condi- 

 tions mentioned above, several readjustments had to be made in the plans for 

 the experiment. The set of fruit was light and scattering and much of it was 

 severely damaged by hail. In the face of such handicaps the results of the 

 season's work cannot be given as much weight as could be desired, but some sig- 

 nificant differences were noted. Yield records were taken on Mcintosh only. 



On unsprayed checks, such fruit as survived the frost and hail damage ripened 

 and dropped prematurely. Practically all of it was infested by curculio, codling 

 moth, and apple maggot and blemished by scab. 



DDT gave excellent control of codling moth. At a dosage of 1 pound Gesarol 

 AK-40 (0.4 pound DDT) per 100 gallons, only 1.5 percent damage was recorded; 

 and at a dosage of 2 pounds, no injury was found. The standard spray schedule 

 in this block held codling moth damage to 3 percent. 



DDT was not as effective against plum curculio as was the standard schedule 

 with lead arsenate, although a combination of lead arsenate and DDT gave 

 somewhat better control than lead arsenate alone. 



No evidence of apple maggot damage appeared in any sprayed plot. 



DDT on Potatoes. Reports that DDT has proved a good insecticide for pota- 

 toes would appear to be borne out in the 1945 tests. A spray contining 0.4 pound 

 DDT (1 pound Gesarol AK-40) per 100 gallons combined with a 10-5-100 

 homemade Bordeaux mixture was used in the test plot. No aphid infestation 

 developed in this plot during the season. There was a very conspicuous reduc- 

 tion in flea beetle damage in the DDT plot, and the highest yield of any of the 

 plots (273 bushels per acre compared with 261 following standard 10-10-100 

 Bordeaux mixture with calcium arsenate). The vines in the DDT sprayed plot 

 showed consistently more vigorous growth and remained green for a longer 

 period than in any other plot. 



The results of these tests in a season of very unfavorable weather conditions, 

 correspond closely with those reported elsewhere. It can be expected that DDT 

 will become an important element in the spray program for potato pests. 



DDT on Onions. DDT spray at 0.4 pound DDT (2 pounds Gesarol A-20) per 

 100 gallons gave 89 percent control of onion thrips, as compared with 90 percent 

 following application of a 4 percent derris powder (4 pounds per 100 gallons) 

 and 91 percent following a fixed nicotine spray (3 pounds per 100 gallons). A 

 5 percent DDT dust gave 90 percent control compared with 81 percent following 

 a 1 percent rotenone dust. 



In a second series, heavy rain a few hours after application appeared to cut 

 down the efficiency of most of the materials. DDT spray gave 82 percent con- 

 trol; derries 83 percent; and fixed nicotine, 80 percent. DDT dust gave 70-}- 

 percent control; rotenone dust, 61 percent. These results indicate that DDT 

 was affected much less by rain soon after application than were the other mater- 

 ials. 



Records of treated plots four days after treatment showed that DDT spray 

 was giving 85 percent control, derris 38 percent, and fixed nicotine 71 percent. 

 DDT dust showed 98 percent control; rotenone dust, 24 percent. Apparently 

 DDT had a considerable residual effect. 



In a third series, the Rohm & Haas wetting agent, Triton X-100, 6 fluid ounces 

 to 100 gallons, was used with all spray materials and made a vast improvement 

 In application and resultant effectiveness. DDT gave 99 -j- percent control, 

 and derris 98.8 percent, in comparison with unsprayed checks. DDT dust 

 gave 93 percent control. 



Further details of these tests will be found under the project "The Value of Control Measures 

 to Supplement the Standard Spray Program for Apple Pests in Massachusetts." 



