2() ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 1952 
of DDT, BHC, and toxaphene in the9oil. Tliese experiments are con- 
tinuing to provide useful in format i<>n oil the disintegration and phyto- 
toxic effects of these materials in the soil. For example, under rela- 
tively unfavorable weather conditions, tobacco yields were reduced in 
1951 in plots in which LOO pounds of DDT had been mixed with the 
soil in 1947. Chemical analyses of the soil in these plots in 1951 in- 
dicated thai only about tO pounds of the DDT remained. Apparently 
DDT and toxaphene in the soil decreased at about the same rate. 
Where 20 pounds of either DI )T or toxaphene were applied to the soil 
each year from 1947 to 1950, inclusive, analyses in L951 showed only 50 
percent of the DDT and 55 percent of the toxaphene remaining. 
About 90 percent of the BHC was lost in the L years. Detailed results 
during the first 3 years have been published in Technical Bulletin No. 
L047. 
New Insecticides Tested Against Several Tobacco Insects 
In Xorth Carolina. South Carolina, Tennessee, and Florida. TDE 
was demonstrated to be the most effective of the available insecticides 
that can be used for the control of hornworms and budworms on 
tobacco. TDE cannot be recommended without reservations, how- 
ever, until it is determined more definitely whether or not it will 
affect the flavor and aroma of the tobacco in the manufactured 
product. Flavor and aroma tests of tobacco products from plants 
treated with various formulations of this material in the Held in 1951 
will be made. Experiments with new insecticides available for ex- 
perimental work indicated that the stereoisomer of dieldrin is the 
most effective insecticide ever tested against hornworms and bud- 
worms. Considerable work will need to be done before it can be 
determined whether or not this experimental insecticide can be used 
on tobacco. 
Ways of Utilizing Enemies of Tobacco Aphid Under Study 
Studies throughout the South to determine the cause and prevention 
of outbreaks of the green peach aphid on tobacco indicate that aphid- 
infested plant beds art' the major source of aphid infestation in 
tobacco fields and that dock and cultivated collard, mustard, and 
related plants growing nearby are the major sources of aphids in the 
plant beds. It has been effectively demonstrated in the shade-grown 
tobacco area of Florida that damage by aphid- in tobacco fields can 
he ureal ly reduced by eliminating these sources of Infestation. Studies 
on diseases, parasites, and predators of the aphid- -how that these 
natural enemies usually keep aphid populations at a low level except 
during the cooler part of the tobacco-growing season. Additional 
evidence has been obtained that the most important factor controlling 
the aphid on tobacco is an unidentified infectious disease which is 
highly lethal when the maximum temperat ure is over 90 F. Parasites 
and predators of the aphid are not effective when the insect is on 
tobacco. An attempt is being made to determine method- of utilizing 
these enemies of the aphid to greater Advantage and thereby to reduce 
the need for insect icides. 
