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inside walls of spray equipment to contaminate the next-used formula, 
are sufficient to reduoe materially leafhopper populations and, thus, 
to increase the yields of sprayed potatoes. The drift effeot was 
distinguishable for a distance of about 8 feet on eaoh side of rows 
treated with DDT»— Wilson and Sleesman (577) • 
In a planting of early potatoes where the potato leafhopper became 
very abundant, four chemical treatments —DDT spray (Gesarol A-20) 4 
pounds per 100 gallons of water (0,8 pounds of actual~"DDT) ; DDT dust 
(Gesarol A-3) 3 per cent j calcium arsenate 4 pounds, with fixed oopper 
(dompound A) 3 pounds per 100 gallons of water j and bordeaux mixture 
5-4-50 -— gave results as follows: Leafhoppers per 16 leaves, 4, 5, 17, 
and 19; European corn borers per 10 potato stalks, 0, 2, 11, and 24; 
yields, bushels per aore, 179, 167, 146, and 116* The averages an the 
controls were 81 leafhoppers, 23 European corn borers, and 110 bushels 
per aore yield*— Wolfenbarger et al* (379 ) • 
Materials tested were 4-percent DDT dust containing 21 percent of 
Miorogel with a 30-70 copper-lime dust, and a Micro gel- calcium arsenate- 
talc (21-30-49) dust* Pour applications were made during the growing 
season at the rate of 30 pounds per aore-applioation (4 replications)* 
Yield of potatoes was 257 bushels on the TDT-Microgel plot as compared 
with 231 on the Miorogel-oalolum arsenate-talo plot* Excellent oontrol 
of this leafhopper was obtained. The control of potato flea beetles 
and Colorado potato beetle with the DDT dust was about equal to that of 
the calcium arsenate dust*— V* J* Agr* Expt. Sta. (275 ) * 
A wettable powder containing 25 percent DDT, 4 pounds per 100 
gallons of water, applied at the rate of 200 gallons per acre at 10-day 
intervals killed all nymphs and increased the yield of potatoes more 
than any other treatment*— Sleesman (321) * 
In experiments conducted in southern Wisconsin a 2*5-peroent DDT 
dust reduced infestations of the potato leafhopper on potatoes and bean6 
78 to 99 percent* These figures were obtained from counts of leafhopper 
nymphs 1 to 3 weeks after application. The DDT dust gave a greater re- 
duction in leafhopper populations than did a dust mixture containing 1 
percent of dinitro-o-oyolohexylphenol and 50 percent of sulfur* 
In similar experiments in the Columbus, Ohio, area DDT sprays and 
DDT-sulfur dusts gave better results than did the dinitro mixture or a 
pyrethrum-sulfur mixture containing 0*025 peroent of pyrethrins and 50 
peroent of sulfur. The DDT sprays contained up to 0*08 percent of DDT 
in a kerosene emulsion, and the dust mixtures consisted of 1*4 peroent 
of DDT, 60 peroent of sulfur, and the remainder pyrophyllite*-- *hite 
(373). 
