- 67 - 
The plants dusted with the 3-Way mixture consisting of pyrethrum, 
rotenone, and sulfur outyielded all the others, both in total yields and 
with highly significant differences as regards first-size potatoes. 
These materials used separately as dusts gave increases in yield over 
the undusted ones, but these were large enough to be significant for first- 
size potatoes only with pyrethrum and rotenone. Perhaps the simplest 
hypothesis to account for the success of the 3-Way mixture is that the 
effect of these different materials is independent and additive; there- 
fore, pyrethrum when used alone increased the yield of first-size potatoes, 
as compered with the undusted, by 37,63 bushels in the acre, the rotenone 
by 26.25 bushels, and the sulfur by 14 bushels, making a total of 77.88 
bushels. This is not significantly different from the 93,38 bushels on 
each acre-increase produced by the combination mixture of these three 
materials. The arrangement of the experiment did not "permit an evalua- 
tion of the insecticidal effects of the Bancroft Clay. On Green Mountain 
potatoes both copper-line and the 3-Yiay dust markedly reduced the 
numbers of leaf hoppers. The untreated vires showed 100-percent injury 
by hoppers, while plants dusted with copper-lime showed only 25-percent 
injur;''; however, the plants treated with the 5-'..t.y mixture s- " only 
10 percent injury on the same date. 
The final results show the highest yields from plants dusted with 
the 3-Y.ay mixture, where leaf/hoppers were best held in check. At the 
peak of leafhopper infestation there were 58 hoppers per plant on the 
plants treated with copper-lime, whereas the 3-Way mixture had reduced 
the.' infestation to 18 on each plant. As no late blight occurred in 
these plots, the higher yield obtained from the 5 -Way mixture compared 
with the copper-lime dust may have been due to the control of some 
insects ether than leafhoppers, although no appreciable numbers of 
other species were apparent, or to the stimulative action of pyrethrum. 
In 1936 on this same field a reduction in yield of 60 bushels on each 
acre resulted from the use of bordeaux mixture. The results of Skaptason 
( 242 ) are referred to in Brimstone Brevities ( 521 ); and Eaude (144) in 
193? recommended the 3-Way mixture for the control of the potato Leaf- 
hopper. 
Howard (150, 151) of the Columbus, Ohio, laboratory of the Bureau, 
reported in February and March 1939 that in comparing the efficiency of 
several dust mixtures and sprays against Empoasca fabae on beans during 
the course of experiments in Ohio in 1S38, it was shown conclusively 
that dusts of undiluted sulfur or a dust mixture made up at the rate of 
90 pounds of sulfur and 10 pounds of pyrethrum containing 0,9 percent 
of total pyrethrins gave best results in controlling this pest. Sprays 
containing basic copper arsenate, basic copper sulfate, sulfur nitride, 
and derris (0,015 percent rotenone) were each ineffective. The addi- 
tion ci peanut butter [not peanut cil] to derris-dust mixtures increased 
their effectiveness. These mixtures were not sc efficient as undiluted 
sulfur or the sulfur-pyre thrum-dust mixture. Pine oil also 5 -ed 
the effectiveness of derris spray but appeared ' 
bean foliage to be recommended for pen era 1 use. 
