ANNUAL REPORT, 1942 39 



Control of Common Red Spider Mite on Greenhouse Plants. (\V. D. Whit- 

 comb, Wm. Garland, and W'm. E. Tomlinson, Jr., Waltham.) Studies of the pH 

 of the sap of several of the host plants of the common red spider mite showed that 

 the lower the pH of the plant sap the less time was required for the mite to de- 

 velop from hatching to adult. These results are based on investigations with 

 rose and carnation plants. Preliminary- experiments with tomato, bean, sweet 

 pea, snapdragon, gardenia, and chrysanthemum have been made and this phase 

 of the work will be continued. 



Among the experimental sprats for the control of the common red spider mite 

 on greenhouse roses, a commercial mixture of gypsum and dicyclohexylamine 

 di-dinitrocyclohexylphenate containing 20 percent of the toxicant, applied two 

 or three times at weekly intervals, gave practically complete control when used 

 at the rate of 24, 20, or 16 ounces per 100 gallons of water with Ultrawet 1-1000 

 as a wetting agent. On unsprayed plants in the same bench, the number of 

 spiders increased 40 percent during the same interval. 



A commercial spray known as technical mannitan laurate reduced the number 

 of live mites 89 percent in four applications at 1-400, and 73 percent at 1-600. 

 Two other rotenone materials gave fair control of the red spider mite and a third 

 material was ineffecti^■e. 



Several of these materials were more effective against the red spider mite on 

 carnations than on roses. 



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

 effect of different amounts of spray on the control of the plum curculio in apples 

 was studied by applying a measured quantity to apple trees of known size. An 

 application of 1 gallon per 100 square feet was significantly more effective than 

 an application of % gallon, but IM gallons per 100 square feet were not consis- 

 tently more effective than 1 gallon, indicating that the results might be influenced 

 by factors other than gallonage. 



Cryolite, 4 pounds in 100 gallons, used as a substitute for the same amount of 

 lead arsenate, gave somewhat less control of the plum curculio in apples, and 

 caused very severe russet on Delicious apples. 



Lead arsenate was used at the rate of 2, 3, and 4 pounds in 100 gallons of spray 

 on Northern Spy for protection against the plum curculio. Results indicated 

 that 4 pounds is necessary for satisfactory control where this insect is abundant. 



Biology and Control of the Grape Plume Moth. (W. D. Whitcomb and Wm. 

 E. Tomlinson, Jr., Waltham.) Experimental dormant applications of the com- 

 mercial DN product Elgetol confirmed previous experiments which showed that 

 a 3^ percent dilution did not give satisfactory control under the same conditions 

 where a 1 percent dilution was effective. 



The effect of pruning in reducing infestation was studied on two vines. Heavy 

 pruning (removing 79 percent of the nodes and canes) destroyed 72 percent of 

 the eggs as compared with 55 percent destroyed by light pruning (ren:oving 50 

 percent of the canes and nodes). 



New Vegetable Insect Pests. (W. D. Whitcomb, Waltham.) The snout beetle, 

 Baris scolopacea Germ., discovered at Arlington in 1941, was quite destructive 

 to Swiss Chard in the vicinity of Waltham. Typical injury cons'sted of egg cavi- 

 ties and feeding punctures in the stems of the chard, making the stalks unsightly 

 and unfit for market. Preliminary trials with applications of rotenone dust 

 indicated that this treatment will reduce the abundance and destructiveness of 

 this insect. 



In the late summer and fall of 1942, several acres of celery, particularly in 

 Arlington, Belmont, WalthaiB, and Woburn, were severely damaged or destroyed 



