ANNUAL REPORT, 1932 31 



The Spray Residue Problem. (A. I. Bourne.) The dry weather that pre- 

 vailed during the past summer again force 1 the problem of spray residue upon the 

 attention of the fruit growers. The rainfall during June was nearly 1 inch less than 

 the normal, and more than half of the precipitation for the month occurred in one 

 storm. There was a deficiency of half an inch in July and of more than li- inches 

 in August. While the rainfall in September was slightly greater than the normal, 

 almost 60 per cent of this amount occurred in two storms late in the month when 

 the Mcintosh crop had been harvested. During October there was slightly more 

 rain than normal. The fact that the greater part of the deficiency in rainfall 

 occurred during the spraying season and extended up to time of harvest ma le the 

 problem acute for early varieties and Mcintosh. The precipitation in late 

 September and October very largely removed the danger in the case of late varie- 

 ties such as Baldwin. This deficiency in rainfall in itself was sufficient to make 

 readjustment of the spray schedules necessary, but its effects were reflected also in 

 the seasonal development of several important pests, notably railroad worm, which 

 made proper timing of late sprays very difficult. 



In many cases growers failed to apply the late sprays necessary for maggot con- 

 trol. Others made these applications only on late varieties. In both cases failure 

 to control maggot resulted. 



Growers who sprayed in late July or early August encountered the problem of 

 residue on Mcintosh in excess of the tolerance or dangerously near it. Growers 

 who dusted in late summer again proved that this ofTers one of the most satis- 

 factory solutions of the problem under Massachusetts conditions at present. 



In preliminary tests a non-arsenical stomach poison showed to good advantage 

 as compared with lead arsenate. This indicates a possible way out of the diffi- 

 culty without forcing the growers to the practice of washing their fruit. 



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

 Department of Chemistry.) The five samples tested this season were all pre- 

 pared with the same emulsifying agents. The oils ranged from a spindle oil to a 

 medium turbine oil and varied in their viscosity from 203 seconds to 619 seconds 

 at 70° F. One sample was an asphalt base oil; the others were of the paraffin base 

 type. These were applied as delayed dormant sprays in the college orchard, to 

 test their comparative efficiency against overwintering eggs of European red mite 

 and their toxicity to the trees. All the samples went into the spray solution with- 

 out difficulty. They showed no tendency to break, even when dissolved in very 

 cold water. Their efficiency as insecticides is noted in the following table. 



Sample Percentage of clusters Number of mites per 



free from mites 100 leaf clusters 



A3 55 70 

 B3 65 100 

 C3 60 87 

 D3 66 67 

 E3 66 73 



All the samples gave practically perfect control. The differences above are 

 too small to be of significance when compared with unsprayed trees which showed 

 an infestation of more than 500 mites on single clusters and averaged more than 

 18,000 mites per 100 clusters. No injury to buds by burning of tissues or retard- 

 ing of growth was noted. 



Apple Maggot Control. (A. I. Bourne.) Apple maggot was more abun- 

 r.ant throughout the entire State this past season and caused more damage than 



