52 MASS. EXPERIMENT STATION BULLETIN 388 



The contrast between spra\ ed and unsprayed specimens of \ iburnum was con- 

 spicuous. (See page 54.) The foHage of unsprayed checks was tightly curled 

 and distorted and the the plants were of little use as ornamentals, while on the 

 sprayed plants freedom from aphid attack allowed full and perfect foliage, a con- 

 dition that is rarely seen in this reg-'on. 



Dormant application of a commercial oil emulsion at 5 percent dilution com- 

 bined with dry-mix DNOCHP gave excellent control of oystershell scale on lilac 

 and willow. Light to moderate infestations were eliminated. On heav}' infes- 

 tations with thick encrustation of the bark, some slight hatching took place but 

 from a commercial standpoint it was negligible. 



Summer Treatments for the Control of European Red Mite. (A. I. Bourne and 

 W. D. Whitcomb.) Another abnormal feature of a very unusual season was the 

 comparative scarcity of European red mite in most orchards in midsummer 

 and late summer. The infestation was negligible in the college orchard. A heavy 

 outbreak in a Berkshire County orchard offered opportunit)- for checking the 

 efificiency of a DN dust (a L7 dicyclohexylamine salt of DNOCHP). The red 

 mite population before dusting amounted to 54.8 mites per leaf. Counts 24 

 hours after treatment showed an average of 9.6 mites per leaf, and similar counts 

 made 8 to 9 days after treatment showed an average of one mite per leaf — an 

 82.5 percent reduction in 24 hours and a 98.1 percent reduction after an 8- to 

 9-day period. 



Tolerance tests of this dust and of a DN spra>' containing 20 percent of the 

 toxicant designed for summer use, on 28 different types of fruit and shade trees, 

 ornamentals, and garden plants subject to mite attack showed no injur\ follow- 

 ing either the dust or the spray. 



In August, tests of new materials for the control of the European red mite 

 on apple were made both at a commercial orchard in Gleasondale and at the 

 Waltham Field Station. The most effective material was a dicyclohexylamine 

 salt of dinitro-ortho-cyclo-hexylphenol mixture containing 20 percent of the 

 toxicant together with dispersing and wetting agent. In four tests of this material 

 at the rate of 20, 24, and 30 ounces in 100 gallons of spray, the average reduction 

 of living red mites was 94.2 percent. There was no significant difference between 

 the dosages used, indicating that the smallest amount (20 ounces in 100 gallons) 

 was adequate. A 40 percent DNOCHP mixture used at 4 ounces in 100 gallons 

 gave 88.1 percent reduction and apparently' lacked sufficient wetting agent. 

 A DN dust containing 1.5 percent of the toxicant averaged 95.3 percent reduction 

 when applied from both sides of the tree and reduced the living mites 89.3 per- 

 cent when the tree was dusted from one side only. 



Five tests of spray materials containing rotenonc averaged 88.5 percent reduc- 

 tion, including one moderately effective combination which gave only 78.7 percent 

 reduction. A pyrethrum spray containing an excellent spreading agent was one 

 of the most effective materials used and reduced an infestation of 20.04 red mites 

 per leaf to 0.69 live mites per leaf, a control of 97.05 percent. A mixture containing 

 ricin, the toxic ingredient in castor-bean, was the least effective material used. 

 None of the materials caused injury to the fruit, bark, or foliage which was ab- 

 normally "hard" following the summer drought. 



