-, 33 - 
Ground derris or cube root has proved effective in killing aphids, 
and has the advantage of loi-; - cheaper to use than nicotine vapor.- . P.o te- 
nor, e insecticides may be applied in either ditst or spfray form with almq&t 
eaually good results, hut dusts are generally preferred because they 
make it unnecessary to haul large quantities of water. The best practice 
is to treat the near- when the first f lover bads appear. Tests made in 
l' ! 3 7 arid IJJiS indicate that roterione-be.&ring products are most effective 
if applied vrhor umiditj is high — that is, when there is a dew or 
shortly after a rain. The best time of the: day is in the morning, late 
afternoon, or evening, rather than midday. The fact that night applica- 
tions are especially effective is presumed to be largely because there 
is generally some dew on the plants at that time, but absence of wind 
at night may also prevent the dusts froE ceinp blown away. 
Another experimental fi\n . ro*i hone dusts are nor? effec- 
tive in killing aphids vrhen the temperature is. above 70° P. In l c 
early applications made in cool weather did cot reduce the number of 
aphids until alter 9 days; "cut as soon as 'temperatures became hither, 
good control resulted within 2- hours. One puzzling fact, which has not 
bt.en explained, is that rotenone seem? to give the vieas some protection 
wnen applied during cool weather, even though the aphids are not immedi- 
ate!:- 'rilled. For this reason it is not possible, without further re- 
search, to say definitely whether it is wise to wait until the tempera- 
ture is above 7C C before using rotenone dusts. 
The Wisconsin Agricultural Experiment Station ( ^l6 ) in 19^? report- 
en excellent control of the pea aphid with sprays of powdered derris 
root. Dusts were not consistently effective. Yields of peas, as record- 
ed at the factor-, showed increases ranging from 62 to 131 percent with 
the various tre; ts, as compared with untreated plots. The average 
increase was 36 percent. In these trials there mas a higher percentage 
of small-sized peas in the check plots than in the treated plots. Trials 
were mad( 0: the late-plant s with concentrations cf J pounds per 
IOC gallons in the fall of 1935* Excellent control cf aphids was a t :ain 
obtain proximately 9? percent of tji°. insects being killed ^oy a 
heavy application of derris spray. One application after the aphid in- 
festation had begun served to Protect tJ ac from' damage for nearly a 
th. trials with 3 - tration erris as low as 1/U to 1/2 
pound per 100 gallons of water with spreaders and wettin - agents - , killed 
appr ; ' bely as largi a percent cf. aphids as did 3 poWls per 100 
gallons^ About 200 gallons of sprs^y was reouired per ^cro. Derris con- 
tai . " - t'of rbtenono :iilad sloval' T over a. ocriod "of 7. ll or 
5 dame, depending en weather .conditions. There was littl. or no repro- 
duction during the period in which a- hide were dying. Indications were 
that when derris sprays were used the plants remained uninfested -f or a 
longer period after treatment than *- r ith any of the other poisons tested. 
The same' station ; 'jlc ,- 319 ) in its annual report for 1077 stated 
that derris- tall a- dust containing 1 percent of rotenone and sprays c.ontai? 
ing from 0.005 to 0.015 percent 02 r t v.oac gave pood control of the 
aphid. Single treatments applied b fori June 15 resulted in large in- 
creases in yield. Of th'< treatmentc applied before June 20, five dust.in, 
tests produced en average increase in yield of IJ'S percent, whereas thre 
spraying tests resulted in an average" increase of 101 percent. Diphenyl 
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