Effect of Disulfoton, Diazinon, and Fensulfothion on Atrazine Absorption by Soybean

Organophosphate insecticides are frequently applied in combination with 2-chloro-(ethylamino)-6-(isopropylamino)-s-triazine (atrazine) to corn (Zea mays L.). The objective of this study was to examine the possible interaction of the Organophosphate insecticides with s-triazine absorption and distribution in the plant. Soybeans (Glycine max (L.) Merrill) were selected for study because they do not rapidly metabolize atrazine. This facilitates measurement of possible interaction effects on absorption and movement from root to shoot in the plant. Combination effects resulting in altered phytotoxicity were measured by preemergence and postemergence application of O, O-diethyl S-2-(ethylthio) ethyl phosphorodithioate (disulfoton) and O, O-diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate (diazinon) to soybeans grown in the greenhouse in the presence of a 1.7 kg/ha preemergence application of atrazine. Preemergence applications of disulfoton increased, whereas post-emergence applications of disulfoton and diazinon decreased atrazine injury. The effect of disulfoton, diazinon, and O, O-diethyl O-(P-(methylsulfinyl)phenyl phosphorothioate (fensulfothion) on the absorption and translocation of ¹⁴C-atrazine was measured in 7-day-old soybean seedlings in nutrient culture following a 4-hour treatment period. Diazinon and fensulfothion reduced the concentration of ¹⁴C-atrazine in the shoots, primarily the stems, of control plants which received the insecticides and atrazine only during the 4-hour treatment period. Under these conditions movement of ¹⁴C in the primary leaves was enhanced by all three insecticides. None of the soybean seedlings grown in 10⁻⁵ M atrazine together with an Organophosphate insecticide and then treated with ¹⁴C-atrazine plus insecticide for 4 hours showed greater atrazine uptake than the control. Under these conditions diazinon reduced the atrazine concentration in the roots. Combination effects of Organophosphate insecticides and atrazine on phytotoxicity appear to involve an effect of the insecticides on herbicide absorption and distribution in the plant.