Herbicide drift

Herbicides can contaminate off-target sites by moving in air as well as in water. Generally, herbicide drift from tractor-mounted sprayers is about 5% to 10% of the material applied, with most off-site deposition occurring within 20m of field edges (Freemark & Boutin, 1995). However, depending on meteorological conditions, application equipment, and physical characteristics of herbicide products, spray drift concentrations of 0.02% to 2% of application rates may occur at distances as great as 400 m from application sites (Fletcher et al., 1996).

The implications of aerial movement of herbicides are especially problematic for highly phytotoxic chemicals, such as sulfonylurea and imidiazoli-none compounds. Although these compounds may have low mammalian toxicity, their drift onto nontarget crops and wild land areas, even at low concentrations, may greatly alter plant performance, particularly reproduction. Fletcher et al. (1996) found that flower and seed production by rapeseed, soybean, sunflower, and Polygonum persicaria could be reduced by exposure to chlorsulfuron at rates from 0.1% to 0.8% of those recommended for field applications to cereal crops. For certain combinations of plant species, chlor-sulfuron rates, and application times, reproductive damage occurred even when effects on vegetative growth were minimal. For example, chlorsulfuron treatment of rapeseed (at 9.2 x 105 kg a.i. ha1) and soybean (at 1.8 x 104 kg a.i. ha1) during anthesis reduced seed yield 92% and 99%, respectively, compared with untreated plants, whereas height was reduced only 12% and 8%. Similarly, treatment of cherry trees with low rates of chlorsulfuron reduced fruit yield but created little or no foliar damage (Fletcher, Pfleeger & Ratsch, 1993).

Other herbicides do not necessarily have such potent effects at low concentrations. Rapeseed and soybean were unaffected by applications of atrazine, glyphosate, and 2,4-D at rates and stages of plant development at which chlor-sulfuron suppressed reproduction (Fletcher et al., 1996). None the less, the experiments with chlorsulfuron indicate that low doses of certain compounds can profoundly affect plant reproduction, and the results emphasize the potential for serious off-target damage due to herbicide drift. Currently, data concerning the impacts of chlorsulfuron and other herbicides on nontarget plant reproduction are not required for product registration in the USA (Fletcher et al., 1996).

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  • Claudio Russo
    What are the characteristics of herbicide drift?
    7 years ago

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