38 MASS. EXPERIMENT STATION BULLETIN 417 



on various host plants particularly beans, lettuce, and cucumber. Significant 

 differences in the life cycle on different host plants were found but they were 

 not so consistently correlated with the pH of the plant sap as in previous studies, 

 indicating that other factors ma}- be involved. About twice as many eggs were 

 laid on beans as on the other host plants in this series. 



Spraj'ing experiments on greenhouse roses showed that 4 applications of 40 

 percent nicotine sulfate 1-400 with or without soap did not control the common 

 red spider mite satisfactorily, but permitted the spider population to remain at 

 about 40 per leaf throughout the experiment. A commercial thiocyanate spray 

 which has been recommended as a substitute for rotenone sprays during the war 

 emergency gave good control of the pest on roses but caused severe injury to 

 foliage even when diluted 1-1200. 



In further experiments with a commercial mixture containing 20 percent 

 di-cyclohexylamine di-dinitrocyclohexylphenate, good control on roses was ob- 

 tained with 3 applications of spray containing }/% ounce and 1 ounce of the toxi- 

 cant in 100 gallons of water, and excellent control with 1 to 3 applications of 

 spray containing 2, 3, or 4 ounces in 100 gallons. About 4 ounces of the toxicant 

 in 100 gallons of water was the critical dosage, and nearly perfect control was 

 obtained whether this amount was applied in several applications at a smaller 

 dosage or in one application at the critical dosage. On carnations the mor- 

 tality was about 30 percent greater than on roses when less than a critical dosage 

 was used but about equal when a dosage of 4 ounces per 100 gallons, or more, was 

 applied. 



No foliage injury from the DN spray occurred on roses or carnations in these 

 experiments. Foliage injury resulted on chrysanthemums and in another series 

 on roses, when this material was combined with a neutral copper (26 percent 

 metallic) fungicide 1-50; and growers have reported injury from this combination 

 during high temperature in mid-summer. 



Napthalene and Similar Compounds as Greenhouse Fumigants. (W. D. 



Whitcomb and Wm. Garland, Waltham.) Experimental fumigations with a 

 mono-dichlornaphthalene-napthalene mixture previously reported were con- 

 tinued, and a series of studies at controlled temperatures and relative humidity 

 was completed. 



Control of Plum Curculio in Apples, (W. D. Whitcomb, Waltham.) In 1943 

 the curculio infestation was the greatest in the history of the Waltham Field 

 Station orchard and 90 to 100 percent of the fruit on unsprayed trees was dani- 



The gallonage experiments in which ^, I, or l}i gallons of spray was applied 

 to each 100 square feet of area of the tree were continued. With the extremely 

 heavy infestation, the ^-gallon dosage was inadequate. The 1-gallon dosage 

 was the best. The lj4-gallon dosage was inconsistent, being the least effective 

 on Wealthy and Spy and the most effective on Mcintosh. 



Cryolite at the rate of 4 pounds in 100 gallons was 12 to 17 percent less effective 

 than lead arsenate at the same rate and russeted the fruit of Delicious badly. 

 DN-Ul at the rate of 1 pound in 100 gallons failed to control the curculio and 

 caused a definite bleaching of the leaf veins following successive applications to 

 tender foliage at the pink and calyx periods. 



New Fruit Insect Pest. (W. D. Whitcomb.) A general outbreak of the spotted 

 tentiform leaf miner {Lithocolletis blanchardella Fabr.) occurred throughout Wor- 

 cester and Middlesex Counties in 1943, with particularly severe infestations in 

 orchards at Marlboro and Groton. Although this insect has been present in 



