Effects of insecticides on acetylene reduction by alfalfa, red clover and sweetclover

Abstract Seven organophosphate and carbanate insecticides were tested for their effects on C 2 H 2 -reduction by alfalfa ( Medicago sativa L.), sweetclovcr ( Melilotus alba L.) and red clover ( Trifolium pratense L.). Plants were grown in vitro for 21 days on nonstcrile vermiculite or soil substrates. Oftanol ® was inhibitory to most plants on both soil and vermiculite. Carbofuran's inhibitory effect was almost entirely limited to soil-grown plants. Carbaryl, aldicarb, chlorpyrifos, and terbufos were inhibitory to certain plants under some conditions. Phosmet was the least toxic. Significant differences were observed in toxicity which were dependent on the growth substrate used. The effects of carbamates tended to be restricted to plants grown on soil substrates rather than on vermiculite. Loss of C 2 H 2 -reducing ability was usually correlated with inhibition of nodule formation. The insecticides did not inhibit growth of Rhizobium meliloti or R. trifolii in broth culture.