Some Insecticides Make

Some Insecticides Make

Soil Toxic To Plants, rr

Others Do Not

How often, and for bow long, some of the new chemical insecticides can be applied to crop land without damaging crop yields is a question being posed these days.

Entomologists at VPI say five ■years' research at the USDA Plant Industry Station at BeltsviUe, Md., has shown that some of the new insecticides remain surprisingly toxic in the soil, while others do not. For instance, 100 povlnds of DDT per acre or more applied to soil in 1945 has lost little of its toxic effect to date. S m a 11 e r amounts applied to crops as needed to control insects accumulate in the soil over the years.

Tests with several different field and truck garden crops showed, too, that many of them are in sode degree sensitive to large doses of insecticides mixed in the soil. All but 3 of 17 garden and field crops grown in greenhouse trials showed some sensitivity to DDT, and seven were classed as highly sensitive. Growth of the crop was reduced as repeated heavy dosages accumulated in the soil, or as increasingly large amounts were applied.

These research findings lead the entomologists to question the heavy continuous use on the same land of the more stable insecticides especially DDT and technical BHC. They emphasize the importance of avoiding careless, excessive, or improper use.

DDT, the first and most widely used of the post-war insecticides was studied more extensively than others. It was found that heavy applications of DDT (about 30 pounds per acre per year) could build up Soil accumulations in 3 to 5 years that would damage the more sensitive crops. Growth of rye in soil from under peach trees that were sprayed three years with DDT and one year with technical BHC, was reduced about SO per cent by the toxic build-up of insecticide, residues in the soil. Some soils that get applications of about 10 pounds of DDT per acre per year may become harmful to sensitive crops within five to ten years.

Limited trials showed technical BRC to be less stable than DDT, but because of its high toxicity to plants in the soil, it is capable of forming damaging accumulations if used often at heavy rates Toxaphene and parathion, however, were found to be so unstable in the soil that they are not expected to accumulate there to a harmful degree following recommended use.

Tests in mineral and much soils common to eastern United States showed that DDT could reach harmful levels in either type, although much more could be applied to the muck than to the mineral soils without injury to crops.

Rem&rtfat,—Only you can

PREVENT FOREST FIRES!