BUREAU OF ENTOMOLOGY AND PLANT QUARANTINE 23 
acres of peas received treatment with insecticides for pea-aphid con- 
trol in Wisconsin during 1951. 
Investigations in Washington, Oregon, and Idaho on the evaluation 
of DDT and other new insecticides for pea-aphid and pea-weevil con- 
trol, in large field plots, resulted in improved methods for controlling 
these insects when they occurred alone or in association. Sprays and 
dusts containing 1 percent of parathion were shown to be very ef- 
fective against both insects. These have largely taken the place of 
dusts containing 5 percent of DDT or 1 percent of rotenone formerly 
used for this purpose. Dusts containing 5 percent of methoxyehlor — 
less likely than DDT to leave harmful residues — were shown to be 
fully as effective against the pea weevil as dusts containing an iden- 
tical strength of DDT. They cost more than DDT and are relatively 
ineffective against the pea aphid. In some localities there was an in- 
dication during 1951 that the pea weevil may be developing a resistance 
to DDT. The use of parathion for the control of the pea aphid and 
the pea weevil has been adopted by the growers on a large scale, a 
total of approximately 27.500 acres of peas being treated with this 
material in Washington, Oregon, and Idaho during 1951. In addi- 
tion, about 7,000 acres of peas were treated with DDT and TEPP. 
Insecticide Reduces Spread of Potato Leafroll Disease by Aphids 
Field experiments in Washington in cooperation with the Washing- 
ton State Department of Agriculture and the Washington Agricul- 
tural Experiment Station to develop methods of controlling the green 
peach aphid on potatoes resulted in the development of a dust mixture 
that gives an almost complete cleanup of the aphids in a few hours 
and reduces the spread of leafroll disease. This disease damages 
both the plants and the tubers and is spread by the aphids even when 
they are too scarce to otherwise cause damage. The dust contains 
5 percent of DDT, 0.5 percent of parathion, and 50 percent of sulfur. 
It is recommended only for potatoes grown in arid or semiarid areas 
as sulfur may injure potatoes in areas of heavy rainfall. In the 
experiments in 1951 this dust gave excellent control when applied by 
aircraft as well as when applied by ground machines. A DDT- 
parathion emulsion spray applied by aircraft also gave excellent 
control. The dust has consistently given better results with sulfur in it 
but evidence was obtained that the sulfur content may be reduced 
to 12 percent without materially affecting the control of the aphid. 
Green Peach Aphid Proves Vector of Foreign Virus Disease 
Investigations in Maryland in cooperation with the Bureau of 
Plant Industry, Soils, and Agricultural Engineering on insect vectors 
of plant diseases disclosed that an abnormality in the development 
of greenhouse-grown chrysanthemums recently imported from Eng- 
land and Denmark was identical with tomato aspermy, a disease 
which had not previously been known to be present in the United 
States. In experiments with tomato aspermy virus, this disease, which 
is mechanically transmitted from chrysanthemum to other hosts, was 
also transmitted by the green peach aphid from tobacco to tobacco or 
tomato and also from chrysanthemum to tobacco or tomato. The 
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