ANNUAL REPORT, 1945-46 3!^ 



The damage caused by abnormal weather conaitions was so severe that yield 

 records could be taken from only 50 feet of row across the north (higher) end of 

 the plots. The crop throughout the entire field was much lower than normal. 



The yield in the plots receiving standard 10-10-100 Bordeaux and 10-5-100 

 Bordeaux was approximately 195 bushels per acre in both cases. Where calcium 

 arsenate was added to Bordeaux, the yield was approximately 35 percent greater. 



The lowest yield occurred where Dithane alone was applied. When calcium 

 arsenate was added to Dithane, the yield was about 50 bushels per acre greater 

 and only slightly less than the yield in the standard Bordeaux plot where calcium 

 arsenate was included and greater than in the low-calcium Bordeaux plots. 

 Dithane appeared to have held blight in check to a degree at least comparable 

 with Bordeaux in spite of the adverse weather conditions and the inferior appear- 

 ance of the plants throughout late summer. 



The highest yield in the entire field was in the plot where DDT was applied 

 (273 bushels per acre compared with 261 bushels per acre following standard 

 Bordeaux plus calcium arsenate). This was in line with the superior vigor and 

 excellent appearance of the plants in this plot throughout the season. 



Reports that DDT is a very good insecticide for potatoes seemed to be borne 

 out in 1945. No aphis infestation developed in the DDT plot although a slight 

 infestation started in other plots. There was a very conspicuous reduction in 

 flea beetle damage and the highest yield in the whole field. The plants were 

 more vigorous throughout the season and remained green longer than in any other 

 part of the field. The results here correspond very closely with those reported 

 from other regions and were so generally favorable that this material may be 

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



Control of Onion Thrips. (A. I. Bourne.) A spray of a 4 percent derris (4 

 pounds per 100 gallons) with Ultra wet wetting agent gave 90.5 percent control 

 of thrips, DDT (0.4 pound per 100 gallons) 89.1 percent control, and Lethane 

 B-72 (3 pounds per 100 gallons) 48.2 percent control, as compared with 91-92 

 percent control following application of Black-Leaf 40 with the same wetting 

 agent. 



A 5 percent DDT dust gave 90 percent control in one test and 93 percent 

 following a heavy application. A 1 percent rotenone dust furnished 81 percent 

 protection, and a Lethane dust (B-71) 78 percent control in light application 

 and 95 percent following a very heavy dusting. 



The wetting agent Triton X-100 appeared to be very well suited for use on 

 the smooth waxy surface of onion plants and improved the effectiveness of all 

 spray materials greatly, derris spraying giving 98.9 percent control, and DDT 

 99.4 percent immediate control with marked residual action. Lethane B-72 

 gave 96 percent control but no prolonged protection. 



No injury was noted following the application of any of the above materials. 



Naphthalene and Similar Compounds as Greenhouse Fumigants. (W. D. 



Whitcomb and Wm. Garland, Waltham.) A paste containing a naphthalene 

 base fumigant was developed for painting on steam pipes to eliminate the use of 

 vaporizing units. Experimental fumigations on carnations with this paste at 

 70°-75° F. for a 6-hour exposure gave satisfactory control of the common red 

 spider at dosages of 6/10 ounce and 8/10 ounce per 1,000 cubic feet, but were 

 unsatisfactory at a dosage of 4/10 ounce per 1,000 cubic feet. Potted cucumber 

 and tomato plants were slightly injured bj' the treatment. 



Biology and Control of the Red Spider Mite on Greenhouse Crops. (W. D. 



Whitcomb and Wm. Garland, Waltham.) Tests of three commercial spray 

 materials containing 5.4 percent and 3 percent rotenone in four applications at 



