34 MASS. EXPERIMENT STATION BULLETIN 398 



DEPARTMENT OF ENTOMOLOGY 

 Charles P. Alexander in Charge 



Investigation of Materials which Promise Value in Insect Control. (A. I. 



Bourne and W. D. Whitcomb.) Work on a cooperative project on investigations 

 of dinitro combinations was concerned primarily with the effectiveness of such 

 combinations against outbreaks of European red mite during the growing season. 



A surprisingly heavy infestation of red mite developed in commercial orchards 

 in practically all sections of the State. Evidences of mite abundance and begin- 

 ning of injury to foliage were noted by mid-June. The attack developed steadily 

 throughout June and reached its peak in most sections by late July and early 

 August. Heavy bronzing of foliage occurred in many orchards, even on varieties 

 which usually were not considered to be particularly susceptible. 



Tests with a DN dust (a L7 dicyclohexylamine salt of DNOCHP) and a DN 

 spray (a dicyclohexylamine salt of DNOCHP + dispersing and wetting agent, 

 used at the standard recommended strength of IJ^ pounds per 100 gallons) 

 were made in nearly all the blocks of the college and station orchard, and in 

 several commercial orchards. L^niformly good control of the mites was furnished 

 by both DN dust and DN spray, and where the applications were made with due 

 care and under suitable spraying conditions no injury resulted. 



Special studies of different strengths of the DN spraj- were made in a block of 

 Baldwin and Wealthy trees. The material was applied at the rate of 12 ounces, 

 16 ounces, and 24 ounces per 100 gallons. All treatments gave good control of 

 m.ites on both varieties. Some slight marginal burn was noted in a few cases, 

 but this was so slight and occurred with such irregularity that it could not be 

 definitely attributed to the treatment and was of no commercial significance. 



Toxicity tests of the DN dust and of the DN spray upon 15 different types of 

 ornamental trees and shrubs resulted in no measurable injury to the foliage of 

 butternut, elderberry, flowering plum, willow, rose, ornamental crabapple, privet, 

 barberry, Norw^ay maple, red maple, evonymus (several varieties) or magnolia. 

 Sumac, raspberry, and grape showed slight to appreciable injury. Fortunately 

 these would seldom require summer application of insecticides of this type. 



At Waltham a commercial DNOCHP material, known as DN-111 and con- 

 taining approximately 20 percent of the toxicant, was used at the rate of 24 ounces 

 and 12 ounces per 100 gallons of water on Baldwin apple trees infested with 

 European red mite. The spray was applied July 23 when the mites averaged 12 

 to 16 per leaf. Both dosages gave good control, and no serious injury to foliage 

 was observed although the margin of some of the tender leaves was slightly 

 scorched. As a result of these experiments and others, DN-111 appears to be a 

 very satisfactory material for the control of summer infestations of the European 

 red mite, and excellent control can be expected from sprays containing as little 

 as 12 ounces in 100 gallons. 



Control of Cabbage Maggot. (W. D. Whitcomb, Waltham.) The natural 

 field infestation of cabbage maggot at Waltham was heavy and caused commercial 

 injury to 88 to 90 percent of the untreated plants of susceptible varieties such as 

 Golden Acre and Copenhagen Market. 



The first eggs were found on May 1 which is about the average date for the 

 last 12 years. 



A study of the relative susceptibility of 13 varieties showed 4 early varieties 

 and 3 medium or late varieties with more than half of the plants severely injured 

 or killed and more than 80 percent commercially injured, while 2 earh' varieties 

 and 4 medium or late varieties had less than half the plants severely injured or 



