ANNUAL REPORT, 1938 57 



None of the maggots covered with 2 inches of soil in laboratory cages emerged 

 as flies, while 18.5 percent of those under 1 inch or less transformed, and 48 per- 

 cent of those on the surface completed their development. 



Experiments with soil treatments applied just before the flies begin to emerge^ 

 as determined by collections of adults in cloth cages covering 15 square feet, 

 indicate that naphthalene flakes either broadcasted on the surface or spaded 

 into the soil gave very good control of midges in the soil. When naphthalene 

 flakes were applied at the rate of 2 pounds to 100 square feet, either by broad- 

 casting or spading, the number of flies emerging was reduced 94.6 percent. Spad- 

 ing alone reduced them 71 percent; Cyanogas at the rate of 1 pound per 100 

 square feet reduced them 86.9 percent; and tobacco powder containing 1 percent 

 nicotine was 60 percent effective. 



The Spray Residue Problem. (A. I. Bourne.) There was no particular spray 

 residue problem in Massachusetts in 1938. Aside from the fact that the Septem- 

 ber storm made windfalls of a large proportion of the crop, the rain which preceded 

 it had removed most of the spray deposit from the fruit. Including the 12 inches 

 of rain which fell in the days immediately before the hurricane, the total precipi- 

 tation from July 30, the date of the last cover spray, until September 21 was 

 16.39 inches. In the 70-day period from the third cover spray to the same date 

 there was an accumulation amounting to 23.09 inches and from the second cover 

 spray the rainfall totaled 28.61 inches. The fruit, therefore, encountered nearly 

 as much rainfall, from the time it received the last full dosage of lead arsenate 

 until the anticipated date of harvest, as the total noimal precipitation from 

 January to August. 



In early September notice was received that the limit of tolerance for lead 

 for the 1938 shipping season had been raised from 0.018 grains per pound of 

 fruit to 0.025 grains; and in November the limit of 0.02 grains per pound, or 

 double the previous tolerance, was announced for fluorine compounds. This 

 action will materially lighten the burden on the fruit grower and allow much 

 greater latitude in the spray program. 



In a study of methods to supplement lead arsenate in the control of orchard 

 pests, experiments with chemically treated codling moth bands were continued 

 in the same orchard as in 1937. In addition to the banding of the trees, the reg- 

 ular spray schedule was supplemented by two extra applications of a fixed nicotine 

 compound in an effort to check late season "stings." There, as in the orchards 

 at the college, the intervention of the hurricane prevented checking the fruit in 

 the experimental blocks. The apples were blown about for such distances that 

 there could be no certainty as to the particular plots from which they originally 

 came, and the fruit was in many cases so badly bruised that minor insect blem- 

 ishes were not distinguishable. By late fall, however, the trees in this orchard 

 had been pulled back into an upright position so that most of the codling moth 

 bands could be removed and examined. 



A total of 3,287 larvae was collected from 210 trees, or an average of 15.7 larvae 

 per tree. In the previous year 4,078 larvae were collected from 248 trees, or an av- 

 erage of 16.4 larvae per tree. The Northern Spy trees in this orchard had prac- 

 tically no fruit in 1937, but bore a full crop in 1938. While the total number of 

 larvae collected in the entire orchard in 1938 was very close to the record in 1937, 

 nearly one half of the number was found on the Northern Spy trees, .which showed 

 an average of 45.5 larvae per tree, while the average for all other varieties was 

 10.5 larvae per tree. Comparison of the collections from the other varieties 

 showed a material reduction in codling moth population in 1938 from that of 

 the previous year. On several trees two bands were set, one above the other, 

 on the main trunk, in an effort to determine what proportion of the larvae moved 



