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Heptachlor Persistence in the Alfalfa-Production Environment

Virginia Polytechnic Institute, Blacksburg

B. L. Samuels and J. W. Midyette, Jr.

Virginia Department of Agriculture, Richmond

ABSTRACT

A field study was conducted to determine the persistence of heptachlor in the environment for alfalfa production when this pesticide was used for control of the alfalfa weevil. The analysis of 1,563 samples of alfalfa hay harvested in the 1964 season from land to which heptachlor had been last applied in the fall of 1961, 1962, 1963, and the spring of 1964, contained average heptachlor levels of 0.017, 0.050, 0.181, and 0.416 ppm, respectively. Results indicate that this pesticide degrades in the alfalfa production environment at a rate such that two-thirds to three-fourths of the average crop residue is dissipated annually. Old alfalfa stands which had received heptachlor applications annually for several consecutive seasons did not contain more residue than younger stands with fewer heptachlor applications, an indication that annual application of this pesticide did not result in any substantial build-up of residue. Application of heptachlor in fertilizer as contrasted with the granular formulation resulted in slightly lower, but nonsignificant, residue in the harvest alfalfa. Crops grown in rotation with alfalfa (corn, sudan, millet) did not contain residues if produced the first season following alfalfa which had received heptachlor treatment.