ANNUAL REPORT, 1929 349 



been directed toward the comparative efficiency of different types of oil 

 sprays for European red mite control, as well as checking them from the 

 standpoint of safety to the trees. 



Against a moderate infestation of red mite, almost all of the oils 

 tested gave satisfactory control, indicating that in general, under such 

 conditions, thoroughness of application and proper timing are more essen- 

 tial than the mere choice of oil s.pray. 



In some cases, after conference with manufacturers, oils were applied 

 at an advanced strength over that previously recommended, in order to 

 meet Massachusetts conditions better. 



The effect of combining certain types of oil sprays with sulfur or cop- 

 per fungicides was studied, both from the standpoint of safety to the trees 

 and of effectiveness against red mite. The results of these tests indicated 

 that these oils can be so used, safely and without impairing their insecti- 

 cidal value. 



The abnormally high temperature in early April afforded opportunity 

 to study the effects of oil sprays for delayed dormant application under 

 conditions very unusual in Massachusetts. The burning which resulted 

 pointed out the posibility of maximum temperature requirements for safe 

 application of oil sprays in addition to the minimum limits with which 

 Massachusetts growers are familiar. 



A study of a recently developed sulfonated, oxidized oil spray was 

 begun, particularly as to its possibilities as an activator for nicotine. 

 Preliminary tests have shown that a dilution of one-half to one per cent, 

 when combined with nicotine sulfate, gives satisfactory control of some 

 insects, with concentrations of nicotine much lower than those at present 

 recommended. This means a material reduction in the cost of such sprays 

 which are at present relatively expensive. 



Control of Onion Thrips. (A. I. Bourne). The summer of 1929 was 

 characterized by conditions of severe drought. Such an abnormally dry 

 season was very favorable for thrips development. Throughout the early 

 summer the infestation was comparatively light and of little consequence. 

 During July and August, when the effects of the continued drought be- 

 came more pronounced, thrips increased rapidly and' many onion fields 

 suffered severely from the combined effects of thrips and dry weather. 

 In the absence of blast and mildew, however, the plants on the whole re- 

 mained green and vigorous considerably later than in the years when 

 those diseases were prevalent. The period of abundance and activity of 

 thrips was proportionally lengthened. 



Some growers became interested in the possibilities of biological con- 

 trol of thrips, purchased a quantity of lady beetles from a western state, 

 and liberated them in a field where thrips were abundant. The effort was 

 not crowned with any conspicuous success. Examination of onion fields in 

 the Valley, throughout the season, resulted in the collection of at least 

 five different species of predacious beetles, all of them well established in 

 this region. The beetles imported from the West belong to one of these 

 species. 



Field tests demonstrated the nicotine-soap combination to be an effective 

 killing agent against thrips, and the machinery for application practic- 

 able. In cooperation with the Department of Botany studies were made 



