Utility of an Insecticide Added to a Fungicide for Soybean during Drought Conditions.

Due to pesticide application costs, many farmers will commonly tank mix a low cost pyrethroid insecticide with a fungicide to save an application cost. Research was conducted at Novelty and Portageville, Missouri in 2011 and 2012 to evaluate the impact of an insecticide (lambda-cyhalothrin at 28 g ai/ha) plus fungicide (pyraclostrobin at 110 g ai/ha) application at the R3 and R5 stages of soybean [Glycine max (L.) Merr.] development compared to insecticide applications made at threshold insect populations. Insect pest populations included 21 different types, while beneficial insects totaled 13 groups over the R3-R7 insect monitoring period. At both locations, rainfall was below normal and none of the threshold monitored treatments reached insect pest populations that warranted an insecticide application during the two years of this research. An insecticide application at R3 decreased pest and beneficial insect populations compared to the non-treated control, while the R5 insecticide application decreased insect pest populations, but had no significant effect on beneficial insects (P=0.13). There was no significant difference (P=0.3) in grain yields for the insecticide and/or fungicide treatments at the four moderate yielding (2,580 to 2,700 kg/ha) site-years. Scouting for insect pests was extremely important to avoid unnecessary crop production expenses especially in drought years where crop yields may be lower than normal.