4 -r.\L REPORTS OP DEPARTMENT OP AGRICULTURE, 1939 
Studies of the influence of particle size, carried on at the Beltsville, 
M<L laboratory, have indicated that extreme fineness is not n 
for the maximum effectiveness of lead arsenate, calcium arsenate, 
cryolite, paris green, or phenothiazine in the control of the codling 
moth. On the other hand, an extremely coarse sample of phenothia- 
zine was much less effective than tin- materials having either a line 
or medium average panicle size. 
The large-scale field tests of baits carried on at Yakima. Wash,, 
in in acres of orchard resulted in the capture of more than 144,000 
moths; yet there was very little difference in favor of the baited 
area in terms of worm injury to fruit at harvest time. Studies car- 
ried on in the baited block by means of the release of marked moths 
indicated that 50 percent of them were being captured in the baits. 
The removal of this large number of moths from the block must have 
reduced the moth population materially, and it is believed that the 
failure to .-how a benefit was the result of movement of moths from 
nearby unbaked areas into the experimental block. At Vincennes, 
End., where the results of large-scale baiting tests w< i what 
similar, studies of moth movement bv means of releases of marked 
moths and their subsequent recapture in traps showed definitely that 
a heavy movement of moths into the baited area took place during the 
summer. 
The mechanical-biological project in West Virginia to control the 
codling moth was continued. The experimental orchard bore a heavy 
crop of fruit in contrast to last year's very light yield. The pro- 
portion of fruit injured by the codling moth dropped from 7:2 per- 
cent in 193T to 63 in 1938, this being largely the result of the in- 
creased number of apples available for worm attack. The per- 
centage of parasitization remained practically the same, whereas the 
percentage of larvae killed by predators increased from 10.5 percent 
in 1937 to 12.€ in 1938. Studies of codling moth predators were con- 
ducted also at the St. Joseph, Mo., laboratory. 
Phenothiazine continued to give control of the apple maggot in 
the Hudson River Valley, when used either throughout th 
or as a final spray following a light program of arsenical applica- 
tions. Ground cube root failed to reduce apple maggot infestation 
in any extent, even though five applications were made Commer- 
cial nieotine-bentonite also failed to control the apple maggot in an 
orchard receiving live applications during the period of adult 
abundance. 
In studies of the common red spider on apple in the Missouri River 
Valley, data were secured confirming results obtained in 1936 and 
i'.i.",7. \ i/. that the thorough application of sulfur materials in the 
calyx and first c6ver sprays effects a marked reduction in popula- 
tions, which appears to delay the spider's increase to outbreak 
proporl ions by 2 weeks or more. 
Further work I done on the pear thrips on prunes in coop- 
eration with theOrefeon Agricultural Experiment Station. In one 
heavily infested orchard two applications of a 2-percent miscible-oil 
emulsion with nicotine sulfate (rave a yield of approximately 6 tons 
nit per acre as compared with less than a ton from the unsprayed 
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