ANNUAL REPORT, 1934 45 



treated to an acid bath in a washing machine were in all cases so cleared of spray 

 residue that even when the complete schedule of four cover sprays (the last one 

 applied in late July) was followed, the fruit showed only traces of either lead or 

 arsenic. 



The season of 1934 was particularly favorable for the retention of sprays on 

 fruit and foliage. Throughout June, July, and early August the rainfall was 

 unusually light and there were no hard driving rains to wash the spray materials 

 from the fruit. Throughout September and early October the rainfall was heavy 

 and consequently late varieties showed somewhat less residue. In a season of 

 more normal rainfall in late July and August the danger from the third cover 

 spray would be materially lessened. 



Results of the present season's tests show that lead is much more persistent 

 than arsenic and constitutes the real problem. Lead residues were in many cases 

 three to four times those of arsenic and were almost always higher than the ratio 

 of lead to arsenic in lead arsenate. It is evident that running fruit through a 

 wiping machine does not remove sufficient residue. Apparently the brushes 

 become more or less covered with the spray material and consequently may 

 transfer the residue from one sample to another. This was definitely proved in 

 the case of a sample of fruit which, although sprayed with calcium arsenate 

 throughout the season, nevertheless showed .002 grains per pound of lead present 

 after being passed through the wiper. Frequent cleaning or replacement of the 

 brushes would be necessary to avoid objectionable accumulations of spray ma- 

 terial. Greater emphasis on reduced dosage in the late cover sprays or the sub- 

 stitution of a dust schedule for the late application offers the best solution of the 

 difficulty as long as lead arsenate continues to be used. 



Systematic Study of Oil Sprays. (A. I. Bourne in cooperation with the Depart- 

 ment of Chemistry.) The three oils used in the 1934 field tests were samples 

 which had been prepared the previous season and held in storage for approx- 

 imately a year. The results obtained furnished data on the insecticidal value of 

 these oils and also demonstrated their stability. All the samples were found to 

 be in perfect physical condition, with no trace of breakdown of the emulsion. They 

 offered no difficulty in preparation and showed no trace of separation and appear- 

 ance of free oil when once diluted with water. They were applied, at a strength 

 of 3 percent basic oil, to a block of young plum trees heavily infested with over- 

 wintering eggs of European red mite, at the delayed dormant stage of bud devel- 

 opment. No trace of injury was noted nor was any check to seasonal development 

 observed. All the samples proved very effective against red mite, as shown in 

 the following table. 



Apple Maggot Control. (A. I. Bourne.) The appearance and seasonal abundance 

 of the insect were watched with considerable interest throughout the season to 

 note the influence of the severe weather conditions of the previous winter upon 

 the insect and the effect, upon the infestation in commercial orchards, of the 

 extensive CWA program of removal of neglected trees in pastures, fence rows, 

 etc., closely adjoining such blocks. 



