Pyroxsulam and Chlorpyrifos Applied the Same Day Injures Wheat

Abstract

Field experiments were conducted in northwestern Kansas for two years to determine the effect of chlorpyrifos application timing on winter wheat response to pyroxsulam applied postemergence. Pyroxsulam at 18.4 g ai/ha was applied in spring when wheat was 10 to 15 cm tall. Chlorpyrifos at 260 g ai/ha was applied 3 or 7 days before, and 3 or 7 days after pyroxsulam application. Also a treatment of pyroxsulam and chlorpyrifos applied on the same day was included. When pyroxsulam and chlorpyrifos were applied on the same day, wheat leaf injury was greatest at 7 days after herbicide treatment (DAHT) (16%) and 14 DAHT (10 to 18%). This was 2 to 10 times higher than the injury caused by pyroxsulam applied alone. Same day application of pyroxsulam and chlorpyrifos also reduced plant height by 8% at 21 DAHT and delayed 50% heading by one day compared to pyroxsulam alone. Chlorpyrifos applied 3 to 7 days before or after pyroxsulam application caused similar or slightly higher leaf injury and growth reduction compared to pyroxsulam alone. Grain yields were not adversely affected by any treatment. To avoid crop injury, at least a 3‐day interval between pyroxsulam and chlorpyrifos applications is desirable.

Response of Wheat Plants to Combinations of Herbicides with Insecticides and Fungicides

“…The high injury observed with the combination pyroxsulam + chlorpyrifos is in accordance with other studies carried out under field conditions. Reddy et al (2010) also observed synergism in the combinations of these pesticides, reducing RT of wheat plants, but without compromising grain yield. Several factors may influence plant response to an herbicide or product combination, such as application stage, climate conditions, and even the differential tolerance presented by cultivars (Everitt and Keeling, 2009;Galon et al, 2010;Robinson et al, 2015).…”