U. S. D. A., B. E. Bui. 109, Part V. T. C. & S. P. I. I., April 5, 1912. 



PAPERS ON INSECTS AFFECTING VEGETABLES; 





ARSENITE OF ZINC AND LEAD CHROMATE AS REMEDIES 

 AGAINST THE COLORADO POTATO BEETLE. 



By Fred A. Johnston, Entomological Assistant. 

 [In cooperation with the Virginia Truck Experiment Station.] 



SPRAYING EXPERIMENTS WITH ARSENITE OF ZINC AND LEAD 

 CHROMATE IN COMPARISON WITH OTHER ARSENICALS. 



In May, 1911, a series of experiments for comparing the insecti- 

 cidal value of arsenite of zinc and of Jead chromate with that of other 

 arsenicals in controlling the Colorado potato beetle (Leptinotarsa 

 decemlineata Say) was undertaken under the direction of Dr. F. H. 

 Chittenden at the Virginia Truck Experiment Station, at Norfolk, Va. 



The season was later than usual, making it unnecessary to spray for 

 the potato beetle until about May 9. At this date no larvae were 

 present on the plants, though beetles and egg masses were abundant. 



On May 9 six plats were sprayed. Table I gives the insecticides 

 and strengths used. 



Table I. — Sprays used against the Colorado potato beetle, Norfolk, Va., May, 1911. 



Plat 

 No. 



Insecticide used. 



I 



II 



III 



IV 



V 



VI 



Lime-sulphur, 2 pounds to 50 gallons of water and 3 pounds of arsenate of lead. 



Arsenate of lead, 3 pounds to 50 gallons of water. 



Lead chromate, 2 ounces to 4 gallons of water. 



Arsenite of zinc, 1J pounds to 50 gallons of water. 



Bordeaux mixture (4-6-50 formula) and 1 J pounds of Paris green. 



Bordeaux mixture (4-6-50 formula) and 1§ pounds of arsenite of zinc. 



On May 22 all of the potatoes were resprayed, the same proportions 

 of the different materials being used with the exception of the lead 

 chromate in which case the strength was doubled. (One ounce to a 

 gallon of water.) 



At this date the larvae were exceedingly numerous and doing much 

 damage in unsprayed potato fields. 



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