Safeners are chemical agents that reduce the phytotoxicity of herbicides to crop plants by a physiological or molecular mechanism, without compromising weed control efficacy. Commercialized safeners are used for the protection of large-seeded grass crops, such as corn, grain sorghum, and wet-sown rice, against preplant-incorporated or preemergence-applied herbicides of the thiocarbamate and chloroacetanilide families. Safeners also have been developed to protect winter cereal crops such as wheat against postemergence applications of aryloxyphenoxypropionate and sulfonylurea herbicides. The use of safeners for the protection of corn and rice against sulfonylurea, imidazolinone, cyclohexanedione, isoxazole, and triketone herbicides also is well established. A safener-induced enhancement of herbicide detoxification in safened plants is widely accepted as the major mechanism involved in safener action. Safeners induce cofactors such as glutathione and herbicide-detoxifying enzymes such as glutathione S-transferases, cytochrome P450 monooxygenases, and glucosyl transferases. In addition, safeners enhance the vacuolar transport of glutathione or glucose conjugates of selected herbicides. The safener-mediated induction of herbicide-detoxifying enzymes appears to be part of a general stress response.

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Absorption, translocation, and metabolism of14C-glufosinate were studied in three annual and two perennial weed species. Young seedlings ofSetaria faberi, Chenopodium album, Cassia obtusifolia, Solanum carolinense, andAsclepias syriacawere treated with foliar-applied14C-glufosinate, and plant tissues were harvested 12, 48, and 72 h after treatment (HAT). Absorption of14C-glufosinate was initially rapid, but increased only slightly after 12 h in all species. Glufosinate absorption was highest inS. carolinense(73% of applied radioactivity), followed byS. faberi(54%),C. obtusifolia(44%),C. album(41%), andA. syriaca(37%) 72 HAT. Translocation of radioactivity out of the treated leaf was species dependent and did not increase much with time in all weed species.S. carolinenseandS. faberitranslocated the highest amounts of absorbed radioactivity out of the treated leaf with 49 to 59% moving to the upper foliage.S. faberitranslocated the highest amount of absorbed radioactivity to the roots (12 to 14%), whileC. albumtranslocated the least (2 to 3%). TLC analysis of plant extracts showed that14C-glufosinate was not metabolized inS. faberi, C. obtusifolia, S. carolinense, andA. syriaca. A glufosinate metabolite with an Rf value matching that of methyl-phosphinico propionate was detected inC. album. Treatment with ammonium sulfate (AMS) increased glufosinate absorption inS. faberiandC. obtusifolia12 HAT, but decreased absorption inC. album. Treatment with pelargonic acid (PA) did not affect glufosinate absorption in any of the species tested. Treatment with AMS and PA did not affect glufosinate translocation in any of the five weed species. Treatment with AMS and PA did not influence the metabolism of glufosinate in any of the five weed species studied. These results show that differential absorption and translocation seem to explain the greater sensitivity of the annual and perennial weeds to glufosinate. Treatment with ammonium sulfate may increase the efficacy of glufosinate in perennial weeds.

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