Previous research has shown that some insecticide seed treatments provide safening effects in rice following exposure to low rates of the herbicides glyphosate and imazethapyr. However, no research has been conducted to determine whether a similar effect may be seen in soybean or grain sorghum, two important rotational crops across the Midsouth. To evaluate the potential safening effects of insecticide seed treatments in these two crops, field trials were conducted in Marianna, AR, in 2015 and 2016, and near Colt, AR, in 2016. In soybean, glyphosate, glufosinate, 2,4-D, dicamba, halosulfuron, mesotrione, tembotrione, and propanil were applied at low rates to simulate drift events, in combination with the insecticide seed treatments thiamethoxam and clothianidin at labeled rates. In grain sorghum, glyphosate, imazethapyr, and quizalofop were applied at low rates in combination with the insecticide seed treatments thiamethoxam, clothianidin, and imidacloprid at labeled rates. Injury reduction was seen at 1 site-year for glyphosate, glufosinate, 2,4-D, dicamba, mesotrione, and tembotrione, and at 2 of 3 site-years for halosulfuron. At 1 site-year, the safening in halosulfuron resulted in increases in both crop height and yield. In grain sorghum, reducing injury via seed treatments was generally more successful. All three herbicides applied in sorghum displayed instances of injury reduction when seed treatments were used at 1 or more site-years, including reducing injury upward of 40% in the case of quizalofop clothianidin at Marianna in 2016. For 2 site-years, injury reduction through the use of insecticides resulted in increases in crop height and grain yield in grain sorghum compared with no insecticide use. Although the degree of safening seen varied depending on site-year in both crops, growers who use insecticide seed treatments on an annual basis may expect to see a safening effect from drift events of most herbicides evaluated in both soybean and grain sorghum.
Nomenclature: 2,4-D; clothianidin; dicamba; glyphosate; glufosinate; halosulfuron; imazethapyr; imidacloprid; mesotrione; propanil; quizalofop; tembotrione; thiamethoxam; rice, Oryza sativa L.; soybean, Glycine max (L.) Merr; grain sorghum, Sorghum bicolor (L.) Moench