ANNUAL REPORT, 1939 59 



total precipitation was only slightly greater than the amount of rain in the single 

 storm which preceded the hurricane of September 1938. During the 4-month 

 period there were only 7 records of piecipitation of 3^ inch or over and most of 

 the rain occurred in light, brief showers which would have little effect upon spray 

 deposits. 



The present tendency on the part of commercial growers to replace lime-sulfur 

 with wettable sulfurs led to a study of the effect of such a practice upon the residue 

 problem. Analyses of the residue on fruit sprayed with wettable sulfur showed 

 less than one-half as much lead and less than one-third as much arsenic as was 

 found on fruit sprayed with lime-sulfur. The visible residue persisting on fruit 

 which received some of the wettable sulfurs was evidently misleading, and the 

 margin of safety represented by the difference in the persistence of spray deposit, 

 particularly in a dry season such as 1939, strongly favors the movement toward 

 wettable sulfurs. 



Studies of supplementary measures to leinforce the spray schedule and of non- 

 toxic insecticides for codling moth control were continued in the same orchard 

 as in 1938. In addition to banding, a commercial fixed nicotine compound was 

 used in the Mcintosh block in late summer sprays to supplement the lead arsenate 

 applications recommended in the regular schedule. Considerably better control 

 of injury by late-season codling moth was secured with the fixed nicotine com- 

 pound than with the regular spray schedule, shown both in percentages of clean 

 fruit and in percentages of fruit showing late season "stings." The improvement 

 due to the addition of the fixed nicotine compound was even more marked in the 

 drops than in the hand-picked fruit. 



The very great reduction in codling moth population was also reflected in 

 band records in this orchard. The total number of larvae collected from 119 

 trees was 411, or an average of 3.4 per band; in contrast with 1,691 larvae col- 

 lected from 103 trees in 1937 and 1,184 larvae collected from 93 trees in 1938. 



Apple Maggot Control. (A. I. Bourne and \V. D. Whitcomb.) The pest was 

 somewhat more abundant than in 1938 and damage was much more prevalent 

 than in 1937. Even the most careful growers throughout the State experienced 

 difificulty in the proper timing of their sprays, and their crop showed more damage 

 than usual. The protracted drought during the period of adult emergence in- 

 terrupted and delayed the appearance of the flies in some orchards. In more 

 favored locations, emergence was practically normal and the recommended 

 schedule of sprays or dusts gave satisfactory control. 



The record of emergence of apple maggot flies from the cages at Waltham 

 is as follows: 



In Sun — Light Soil 



CultivEted Sod 



1st fly June 26 July 4 



25% emergence July 7 July 11 



50% emergence July 15 July 14 



75% emergence July 20 July 19 



Last fly Aug. 7 Aug. 1 



Insecticides for the Control of European Corn Borer. (A. I. Bourne.) Weather 

 conditions during May were very nearly normal, and on the whole were favorable 

 for the development of both corn and the corn borer. The last frost occurred on 

 May 16, the daily temperature was comparatively high, and from the 20th to 

 the end of the month the minimum temperatures with but few exceptions were 

 50° F. or above. During that period there was only one storm of any conse- 

 quence, so that pupation and moth emergence took place normally and there was 

 little or no interference with egg deposition. The month of June was also very 



