ANNUAL REPORT, 1938 55 



Control of White Apple Leafhopper. (W. D. Whitcomb, Waltham.) The white 

 apple leafhopper was generally abundant in Eastern Massachusetts orchards. 

 In some orchards infestations as high as 25 hoppers per leaf developed and in 

 others the average was 1 to 4 hoppers per leaf. 



A finely ground dust containing 55 percent sulfur and .123 percent pyrethrins 

 was widely used. In most cases this dust gave good control, but the results 

 varied with the thoroughness of application and the weather conditions when 

 applied. Actual counts in one orchard where this dust was applied to three differ- 

 ent blocks of trees on different days showed reductions of 96.94 and 76.19 percent 

 in the number of live hoppers per leaf on Mcintosh, and 51.13 percent on De- 

 licious. In the experimental orchard, counts two days after application showed 

 that the sulfur-pyrethrum dust gave 88 percent reduction of hoppers and was 35 

 percent more effective than a standard pyrethruni-clay dust (30-70) containing 

 about twice as much pyrenthrins. 



Nicotine sulfate 1-800 with or without soap and a pyrethrum extract containing 

 2.2 percent pyrethrins 1-800 with either fish oil soap or cocoanut oil soap all 

 reduced the leafhopper population more than 90 percent. When counts were 

 made 10 days after the application, however, the nicotine sprays had maintained 

 the high percentage of reduction while the hopper population on the pyrethrum- 

 sprayed trees had increased by 16 and 25 percent, indicating considerably more 

 residual effect from the nicotine. A commercial oil-pyrethrum mixture 1-600 

 (DX) maintained its high degree of control for 10 days, but cube powder with 

 resin residue emulsion, an oil-rotenone mixture (Standard Chem. Co.) 1-800, 

 and a dinitrophenol material (cyclonox) 1-800 and 1-400 permitted a slight in- 

 crease in hopper population 10 days after application. 



Control of Plum Curculio in Apples. (W. D. Whitcomb, Waltham.) In spite of 

 abnormally warm weather early in the spring, the maximum emergence of the 

 plum curculio and the critical period in its control did not occur in 1938 until 

 June 6 to 13, about 3 weeks later in relation to tree development than normal. 

 The usual application of the first cover spray was made May 20 to 25 with good 

 results, but the delayed activity necessitated another application June 8 to 10 

 which was not called for in the recommended schedule. 



During the period from May 19 to 27, trees in the experimental orchard were 

 sprayed when the fruit on them had grown to approximately 4/16, 5/16, and 

 6/16 inches in diameter. An e.xamination of 19,000 apples showed noticeabh 

 better protection when sprayed at the 5/16-inch size even though these applica- 

 tions were made on successive days. On Gravenstein the application at 4/16-inch 

 size permitted 13 percent more curculio injury and was apparently too early; 

 and the application at 6/16-inch size showed 16 percent more curculio injury, 

 being apparently too late. On Mcintosh, the apples sprayed at 5/16-inch size 

 were damaged only about one-half as much as those sprayed when the fruit was 

 6/16 of an inch in diameter, and about one-third as much as the 4/16-inch size 

 fruit. 



During this period (May 19 to 27) the apples grew approximately 1/16 inch in 

 diameter each day, indicating the great importance of timeliness of application 

 for curculio control. 



Apple Maggot Control. (A. I. Bourne and W. D. Whitcomb.) Apple maggot 

 proved to be more abundant than in 1936 or 1937, and even in well-sprayed 

 commercial orchards the pest was present in greater numbers than would be 

 expected following a thorough spray or dust program. This was due in part to 

 the fact that many growers relaxed their vigilance and took less care in the prompt 

 disposal of dropped apples. The decline in numbers of the pest in the last few 



