Effect of Insecticide Placement on the Phytotoxicity of Planting Time Insecticides and Their Interaction with Herbicides

Abstract

Experiments were conducted to determine the influence of insecticide placement on phytotoxicity to sugarbeet. A greenhouse study showed that post planting chlorpyrifos application did not damage sugarbeet as much as similar applications at planting. The lack of differences in sugarbeet injury between the placement of chlorpyrifos in the furrow (T-band) and on the surface indicates that surface applications can cause significant damage. In two field studies we found that insecticide placement was an important factor in determining the potential for insecticide phytotoxicity on sugarbeet. The greatest injury was obtained when chlorpyrifos, fonofos, and terbufos were placed behind the furrow openers and in front of the press wheel. This placement would be the most likely to result in closer association between the insecticide granules and the seed. Both the modified in-furrow chlorpyrifos treatment and the band in front of the press wheel resulted in substantial sugarbeet damage, even at the lower rates. Insecticide bands ahead of the planter unit resulted in intermediate damage. Band applying the insecticides to the rear of the press wheel resulted in the least phytotoxicity. Apparently, the sealing action of the press wheel reduces the contact with the seed and prevents the insecticide from mixing in the upper layers of the soil. Insecticide placement behind the press wheel provided the best protection from phytotoxicity ; however, even this placement did not eliminate the potential for phytotoxicity.