Pesticides in the Environment-76
 

 

 

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Project Leader and Principal UC Investigators

Glenn Nader, livestock farm advisor, UC Cooperative Extension Butte/Sutter/Yuba Counties

 

Concern for the environment has characterized the California rice industry for many years. Although 1.7 million pounds of insecticides, fungicides, and herbicides were applied in 1974, that was actually 22% LESS chemicals per acre than in 1970!

Over the same period, the number of listed compounds declined from 58 to 28. Consistently the most important and widely used were the weed killers propanil, MCPA, and molinate (Ordram). Determining which chemicals are safe, and using minimum amounts at greatest efficiency, are prime goals of the rice growers. Cumbersome EPA procedures make registration of new compounds difficult or impossible, discouraging the chemical companies and the growers. Research on the fate of rice pesticides by the UCD Toxicology Laboratory looms as more important than ever in demonstrating the effectiveness and safety of present and prospective chemicals. The ultimate registration of Bolero, Basagran, and Du-Ter will depend on coordinated research efforts in the projects supported by the Board.

The mobility of such chemicals as propanil, following their application emphasizes the need for a "balance sheet" account of their location and movement.

During the late 1950's, MCPA established its effectiveness as a control agent for such troublesome weeds as water plantain, arrowhead, and bulrush. Later, propanil (Stam) and molinate (Ordram) brought control of watergrass, with accompanying spectacular increases in rice yield. At economically practical pesticide application rates, residues in the crop were well within the health tolerances set by federal and state agencies.

While rice pesticides are considered to be "nonpersistent," in contrast to more long-lasting ones (DDT), knowledge of what actually becomes of them is essential. The environmental fate of the chemicals can become of sudden and dramatic importance, as demonstrated by the problems raised several years ago by propanil drift. Recent UCD research indicates that the undesirable leaf spots observed in orchards near fields where propanil had been used may be due to minute particles of crystalline propanil dislodged from the rice plants and carried out of the field by wind for days after application.

Continued registration of MCPA was made possible by information from an "accounting" of what happens to chemicals used in agricultural applications.

Working with a normal aerial application of MCPA to a commercial rice field, UCD workers showed that the transfer of the chemical to, and movement in the air, was negligible, and that breakdown of the herbicide to identifiable nontoxic fragments occurred primarily in water-from the action of sunlight and microbes. Parent MCPA reached environmentally acceptable levels within 14 days. Without these data, the registration of MCPA for continued use on rice would not have been possible, and public concern over contamination of the environment might have proved fatal to its continued use.

Vital impact data on molinate are being gathered from studies which will be important for retaining its registration.

Similar to the work done on MCPA, this study was one of the most comprehensive accountings ever developed for a pesticide. It showed that soil, aquatic breakdown by sunlight, and decomposition by living organisms each accounted for only about 5% of the applied herbicide. The remainder volatilized harmlessly into the atmosphere.

 

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