ANNUAL REPORT, 1941 59 



plant and remained at that low level until late August when the plants matured. 

 No blast was observed. 



Throughout the Valley, fields of both set and .seed-grown onions were com- 

 paratively free from thrips. Results of tests of contact insecticides for thrips 

 control were inconclusive because of the scarcity of the insects even on the un- 

 sprayed plants. Fixed nicotine with a resin residue spreader gave good initial 

 control although its action was slower than that of nicotine sulfate, it was as 

 effective alone as when used with a spreader. A rotenone extract with resin 

 residue spreader had a high immediate effect and good residual action. Derris 

 powder (4 percent rotenone) gave excellent kill within 24 hours, and reinfestation 

 was slow. This was true regardless of the type of spreader used. Nicotine sulfate 

 and soap caused the usual high mortality of thrips within a few hours after appli- 

 cation but its residual effect was inferior to that of rotenone. 



Predaceous insects were comparatively scarce during the early summer, but 

 by mid-August syrphid flies and predaceous thrips had increased to considerable 

 numbers and contributed very greath' to the rapid decline, in late August, of a 

 very light but long-drawn-out attack of thrips. No evidence of fungus disease 

 of thrips was observed. 



The Spray Residue Problem. (A. I. Bourne.) The more liberal limits of 

 tolerance established in the late summer of 1940 continued in effect for the ship- 

 ping season of 1941. While the present limits are calculated to allow the growers 

 greater latitude in their pest control program, the prolonged drought from late 

 July until harvest and the uncertainty as to the permanency of the present 

 limits made growers reluctant to enlarge their spray program, and for the most 

 part very few changes were made. In the spray program recommended by the 

 college foi 1941 the only significant change was the suggestion of a 75-25 sulfur- 

 lead arsenate dust as an alternate for the 2d cover spray. 



Through the cooperation of the Control Service, analyses were made for lead 

 and arsenic residue on samples of Mcintosh collected from the sprayed plots at 

 harvest. These analyses showed the amount of residue to be in all cases well 

 below the present limits. 



PVuit which had received the standard sclietlule recommended for the State 

 showed residues of .031 grains of lead and .013 grains of arsenic per pound of 

 fruit. Samples from the optional standard schedule in which no lime was used 

 in the cover sprays gave .026 grains of lead and .009 grains of arsenic per pound. 

 In the plots where wettable sulfur was used throughout the season, the lead 

 residue ranged from .023 to .037 grains per pound and the arsenic residue from 

 .005 to .015 grains. Lead arsenate was applied in the 2d cover spray (June 10) 

 at 4 pounds per 100 gallons; 3 pounds in the 3d cover (July 2); and 2 pounds in 

 the 4th cover (July 29). The fruit was picked September 15. While the total 

 precipitation for July was nearly normal, approximately half of it occurred in 

 one shower on the 28th. Records showed that during August and September 

 little more than half the normal rainfall occurred, a deficiency of 3.67 inches. 

 Fruit encountered unusually favorable conditions for the retention of spray 

 deposits and normal weathering off could not take place. 



Even under such a severe test as the past season offered, lead and arsenic resi- 

 tlues were so far below present limits that there was a substantial margin of safety, 

 which would indicate that if these limits are retained the growers will have more 

 latitude for stiffening their spray schedule for late summer pests than they have 

 enjoyed since spray residues became a problem of major importance. 



Apple Maggot Control. (A. 1. Bourne and W. D. Whitcomb.) Apple maggot 

 proved to be of relatively minor importance in 1941, not only in Massachusetts 

 but throughout most of the Northeastern States. In well-sprayed commercial 



