ANNUAL REPORT, 1947-48 43 



In comparison with the control logs, 100 percent prevention or control was 

 obtained with No. 2 fuel oil alone, pentachlorophenol in No. 2 fuel oil (1-10 by 

 volume), and monochloronaphthalene in No. 2 fuel oil (1-12 by volume). The 

 one percent DDT wettable powder spray and the orthodichlorobenzene in No. 

 2 fuel oil (1-8 by volume) gave 91.6 and 84.2 percent prevention, respectively, 

 based on the number of exit holes per square foot of bark; but on the basis of 

 the number of exit holes per egg gallery (with and without hatched eggs) 76.6 

 and 79.9 percent control, respectively, was obtained. 



Spraying to Prevent Twig Feeding by the Smaller European Elm Bark Beetle. 



(W. B. Becker.) Several new insecticides were tried in four types of spraying 

 applications to prevent twig feeding on American elms by the smaller European 

 elm bark beetle, Scolytus multistriatus Marsham, using the method described on 

 pages 41-42 of last year's annual report (Bulletin 441). 



1. With Small Compressed-air Garden Sprayers. The sprays were applied 

 thoroughly at close range to low-growing branches of elms. Dormant and foliage 

 applications of commercial DDT emulsion and wettable powder sprays at the 

 low strengths found successful against many defoliating insects did not give good 

 protection against S. multistriatus twig feeding after many days of weathering. 

 No spray injury resulted to the elms at these low concentrations. 



Dormant applications: Higher concentrations of several commercial DDT 

 emulsions gave increasingly longer protection on the sprayed portions of twigs. 

 Good protection for 100 days was sometimes obtained with 1 percent DDT 

 emulsions, but much less often with 0.5 percent; while 2 percent DDT emulsions 

 were effective for 200 days. The addition of lead arsenate to DDT emulsions 

 (38 grams per gallon of 0.5 percent DDT spray) made no great difference in the 

 results obtained at that strength. A 4 percent chlordane emulsion did not re- 

 main effective so long as a 1 percent DDT emulsion. No spray injury to the 

 elms resulted from any of these dormant applications. 



Foliage applications: In mid-August, 2, 1, and sometimes 0.5 percent com- 

 mercial DDT emulsion and wettable powder sprays applied to previously un- 

 sprayed elms gave complete protection on sprayed parts of twigs for 109 to 113 

 days, after which these tests were suspended. No spray injury to the elms re- 

 sulted from the wettable powder sprays, but slight foliage injury resulted from 

 some 1 percent commercial DDT emulsions and moderately severe injury from 

 some 2 percent DDT emulsions. Sugar maples and some other plants growing 

 next to sprayed elms were injured more than the elms by these sprays. Spider 

 mite damage sometimes followed DDT applications to elm foliage. A 2 percent 

 chlordane emulsion gave much shorter protection and caused no injury. Wet- 

 table powder sprays of benzene hexachloride (151.4 grams of a 50 percent wet- 

 table powder per gallon), Ryania SC50 (76 grams per gallon), and Ryanex 

 (151.4 grams per gallon) gave still less protection but caused no injury. 



2. With High-powered Hydraulic Sprayers (35 gallons a minute capacity) : 

 Only DDT emulsions, commercial and laboratory-prepared, were used in this 

 equipment. On low branches protection was somewhat comparable to that 

 reported for DDT emulsions in the previous section. The principal difficulty 

 lay in obtaining equally long-lasting protection in the upper parts of the elms, 

 even though the spray always reached over the tops of the trees, which were up 

 to approximately 60 feet high. As much as 25 gallons of spray was used on in- 

 dividual elms of medium size for thorough coverage. 



