Performance of Soil Applied Insecticide in Corn Production Since 2005.

The larval stage of corn rootworm (CRW) (Diabrotica virgifera) feeds on corn roots and can drastically reduce the plant root mass resulting in water or nutrient stress, lodging and reduced yields. The objective of this study was to evaluate the use of a soil applied insecticide on corn. Forty three on-farm replicated strip trials spread across Iowa were conducted from 2005 through 2015. The treatments consisted of tebupirimphos and cyfluthrin (Aztec®) applied in-furrow with a farmer chosen hybrid that had CRW Bt corn trait and an untreated check with the same hybrid. From 2012 to 2014 plant roots were collected to assess the damage from CRW feeding. On-farm trials were harvested by farmers’ combines equipped with yield monitors and GPS. A power analysis was conducted to estimate the numbers of years, trials locations, and replications in the future trials. Across 43 trials the average yield increase from the insecticide was 188 kg ha^-1 (90% CI from 127 to 222 kg ha^-1). The yield increases varied between years with 2012 being the highest at 605 kg ha^-1 and 2015 being the lowest at 54 kg ha^-1. The yield responses tended to be greater in locations with lower early season rainfall. In addition, the site-specific responses were lower when stacked hybrids were planted or corn was planted after soybean.  These evaluations are important to help farmers making decisions whether to use or not use soil applied insecticide.