J.C. Hall

Factors affecting the herbicidal activity of glufosinate-ammonium: absorption, translocation, and metabolism in barley and green foxtail.

Abstract 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.

Physiological and biochemical investigation of the selectivity of ethametsulfuron in commercial brown mustard and wild mustard

Abstract Under controlled environment conditions, ED50 values (dose required to reduce growth by 50%) determined from total plant dry weights in response to foliar-applied ethametsulfuron (DPX-A7881; (methyl-2-[(4-ethoxy-6-methylamino-1,3,5-triazin-2-yl)carbamoylsulfonyl]benzoate) were 148 and 0.85 g ai/ha for commercial brown mustard (Brassica juncea) and wild mustard (Sinapis arvensis), respectively. There was little or no difference in absorption of the herbicide between the two plant species, with >95% absorbed after 12 hr in both species. Approximately 8 and 10% of the recovered radioactivity was translacated out of the treated leaf 72 hr after application to commercial brown mustard and wild mustard, respectively. Acetolactate synthase extracted from the two species was equally sensitive to DPX-A7881 (I50 approximately 15 nM), indicating that selectivity was not due to differences in the herbicide target site between the two species. DPX-A7881 was metabolized more rapidly in commercial brown mustard than in wild mustard; approximately 38, 27, 20, 5, 2, and 3.5% of the recovered radioactivity remained as DPX-A7881 in commercial brown mustard and 64, 57, 35, 29, 25, and 19% remained in wild mustard 12, 24, 36, 48, 72, and 96 hr after treatment. Two common metabolites were formed in each species; one of these accounted for 93 and 67% of the extractable 14C activity in commercial brown mustard and wild mustard, respectively, after 72 hr. The second metabolite constituted less than 25% of the recovered 14C activity at all sampling times, with little difference between the two species. It is proposed that this difference in the rate of metabolism of DPX-A7881 may constitute the basis of selectivity of the herbicide between tolerant commercial brown mustard and sensitive wild mustard.