Corn Herbicide and Soil Insecticide Interactions

Mark VanGessel, Extension Weed Specialist; mjv@udel.edu

Last year a few farmers had severe corn injury because they had used an organophosphate insecticide and an ALS-inhibiting herbicide at planting. Remember, there a number of corn herbicides that have label precautions about use when an organophosphate insecticide is used at planting. The herbicides include both soil-applied and postemergence herbicides. This includes the insecticides Counter (terbufos), Lorsban (chlorpyrifos), and Fortress (chlorethoxyfos). The list of herbicides is quite extensive and includes multiple herbicide families so follow this link for a detailed list of herbicides http://www.rec.udel.edu/weedscience/CornGuideWeb/CornLinks/CornTable19.pdf

Unfortunately, most corn seed companies no longer designate hybrids as either IT or IR. So if you are not sure, take the cautious approach and assume the hybrid is a “standard” hybrid (no enhanced tolerance for imidazolinone herbicides); and follow the most restrictive guidelines.

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