FACTORS AFFECTING THE HERBICIDAL ACTIVITY OF GLUFOSINATE-AMMONIUM - ABSORPTION, TRANSLOCATION, AND METABOLISM IN BARLEY AND GREEN FOXTAIL

The absorption, translocation, and metabolism of glufosinate-ammonium were investigated as possible explanations for the difference in sensitivity between susceptible green foxtail (Setaria viridis (L.) Beauv.) and more tolerant barley (Hordeum vulgare L.). In a controlled environment growth room (450 μE m-2 sec-1 light, 16-hr photoperiod, 25°C day/16°C night, 65% RH), the effective dose for reduction of growth by 50% (ED50) was 65 g/ha for green foxtail and 500 g/ha for barley. Tolerance of barley increased with growth stage while green foxtail was equally sensitive at all growth stages tested. Accumulation of ammonia in green foxtail and barley treated with 100 g/ha of glufosinate-ammonium preceded the onset of visible injury symptoms by at least 24 hr, and the level of ammonia in the plants correlated with the sensitivity of the plants to glufosinate. Radiolabeled glufosinate-ammonium applied to a young expanded leaf was absorbed at a significantly higher rate by green foxtail than by barley. Translocation of radiolabel from the treated leaf into the shoot and roots was also significantly greater in green foxtail. Thin-layer chromatographic separation of radiolabeled shoot and root extracts indicated that metabolic degradation of the herbicide did not occur in either species. The difference in sensitivity between the two species was associated with differences in uptake and translocation, not with metabolic degradation. © 1990.