ANNUAL REPORT, 1930 257 



crease in jield resulted from dustinu-. Yields were increased somewhat by 

 applications of Bordeaux sprays. Onion fields in the Valley were observed 

 at frequent intervals during the growing season to note the appearance an3 

 extent of disease and insect pests. No instance of blast or mildew was dis- 

 covered. Dry weather and a moderate infestation of thrlps were the chief 

 factors aflfecting the crop. 



Control of the Plum Curculio in Apples. (W. D. Whitcomb, AValtham). 

 Although fruit growers secured l>etter control of the plum curculio in 

 1930 than in recent seasons, this appeared due to cumulative benefits 

 from improved control measures and timely spray applications rather 

 than to a noticeable increase in natural mortality. Tlie infestation, de- 

 termined by the number of larvae emerging from one bushel of un- 

 sprayed dropped apples in 1930 was 3047, compared with 3137 in 1929, 

 and 2379 in 1928. 



Preliminary studies of the effect of temperature on the activity of the 

 plum curculio showed that beetles confined at temperatures above 70° P. 

 made three times as many punctures (1991) as those held below 70° F. 

 (629). The corresponding number of punctures at normal outdoor tem- 

 peratures was midway between the two extremes (1191). 



The effect of maximum daily temperatures on curculio activity as de- 

 termined from insectary records of the past four years is variable yet 

 shows an average increase of 12 to 27 punctures per day for each 10° rise 

 in temperature. 



Beetles feeding on well-sprayed fruit of normal size at the time of the 

 calyx spray lived 10.6 days, and when supplied with normal fruit one 

 w^eek later they lived 10.3 days. With sprayed fruit gathered two weeks 

 and three weeks after the petal-fall period for food, the beetles died in 

 4.9 days and 3 days respectively. 



In both laboratory and field experiments, barium fluosilicate and syn- 

 thetic cryolite failed to control the plum curculio as well as eqiial amounts 

 of lead arsenate. Chemical hydrated lime added to the lead arsenate- 

 lime-sulfur combination spray was also less effective than the standard 

 solution. Molasses, fish oil, or linseed oil used as a sticker with lead ar- 

 senate was more effective than flour paste or calcium caseinate. An 85-15 

 sulfur— lead arsenate dust was very effective in the laboratory, but barium 

 fluosilicate-lime, cryolite-lime and naphthalene-lime dusts failed to kill the 

 beetles. 



The Spray Residue Problem. (A. I. Bourne). Another season of light 

 rainfall again emphasized the necessity of careful arrangement of the 

 spray schedule in order to avoid arsenical residue on fruit at harvest, 

 in excess of the established limit of tolerance. Rainfall was considerably 

 below normal, although the deficiency was not as great as in 1929. The 

 fact that the greatest shortage was in late July and August was of con- 

 siderable significance, since it followed the sprays applied in late July for 

 apple maggot and codling moth control, increasing the risk of residue 

 from those applications. 



Attention w^as centered chiefly upon commercial orchards where the 

 schedule included one or two July applications of spray, and on those 

 which were dusted once or more in August. Cooperative tests of differ- 

 ent dust materials were made in one commercial orchard. 



Analysis of fruit from these orchards shows that in a season such as 



