~)2 INNTTAL REPORTS 01 DEPARTMEN1 01 AGRICULTURE, 1951 
growth of various crops. Experiments were begun at Florence, S. C, 
in the spring of L947, in cooperation with the Bureau of Plant Indus- 
try, Soils, and Agricultural Engineering and the South Carolina Agri- 
cultural Experiment Station, to determine the effects of aoil 
applications of three insecticides on five crops grown in a 3-year ro- 
tation. Results of the first 3 years of the experiments have now been 
anal} zed. 
The same soil treatments and the same crop successions were used 
in each of three randomized-block experiments. Each experiment, 
however, was started with a different crop — tobacco, cotton, or cow- 
peas. In this manner, tests were made on all crops each year. Tobacco 
was followed by a mixture of oats and Austrian winter peas, by cow- 
peas the second spring, by rye the second fall, by cotton the third 
spring, by rye the third fall, by tobacco the fourth spring, and by 
oats with Austrian winter peas the fourth fall, the same crop cycle 
I eing followed in each plot. 
Each of the 3 experiments involved the application of 10 and 20 
pounds of DDT an acre cadi spring, following dosages of i" and LOO 
pounds in L947 only. Cotton did not seem to be affected by ani of 
the treatments except the LOO-pound dosage applied in 1947. This 
dosage appeared to cause some chlorine injury, characterized by glossy 
brittle leaves, in L947 and to affect the yield and burning quality of 
the L9 L9 tobacco crop. 
All except the tO-pound dosage of DDT affected cowpeas to some 
extent. The effects were not apparent until l ( .»l s . The LOO-pound 
dosage reduced the yield of cowpeas in the hull in 1948 and reduced 
the -tand of the plants in L948 and L949. The K)-pound dosage did 
not significantly affect the cowpeas in any year, but the yield of hay 
and pea- in the hull was lower than that from the untreated check 
in r.> In Three annual applications of LO or 20 pounds an acre reduced 
the stand and growth of the cowpea plant-. Tin' 1' pound dosage 
seemed to retard the growth of a mixt ure of oat- and Austrian winter 
peas. Rye was susceptible t<> injury by DDT. and even a total id' 30 
pounds applied over a 3-year period reduced growth under some 
condit ion-. 
Toxaphene at 20 pound- an acre annually was less injurious to the 
i lirrc nop- than DDT at the same dosage. 
Each experiment also included tests \\ it li technical benzene hexachlo- 
ride, containing 12 percent of tin 1 gamma isomer, applied annually 
;il L6.7 pound- an acre, and at L2.5 pounds with 2.5 pound- <>t' DDT. 
Iii 1'.' 1 7 benzene hexachloride was applied also at 83.3 pound- an aire, 
and ai 50 pound- with 1" pound- of DDT, All tin' treatments af- 
fected tin- flavor of the tobacco in 1947, the only year in which the 
flavor was checked. Tin- 50- and s :>.."> pome I dosages reduced the stand 
of .1 root knot resistant variety of tobacco in 1947, when the plants 
transplanted shortly after the insecticides had been applied. In 
1948 and L949, when a root knot susceptible variety was grown, all 
dosages gave some control of the root knot nematode. Also in L949 a 
slightlj higher yield was obtained from the plots that had received the 
two heaviest dosages in 1947. All dosages reduced the 1947 stand of 
cotton planted shortly after the insecticides had been applied, hut in 
subsequent years none of tin- treatments harmed the cotton. The 
benzene hexachloride did not seem to injure rye so much a- did DDT. 
