Over the past few years, a few fields have been treated with an organo-phosphate insecticide and then with an ALS-inhibiting herbicide and significant injury has occurred. A number of corn herbicides have label precautions about use of an organo-phosphate insecticide at planting due to potential crop injury. This includes the insecticides Counter (terbufos), Lorsban (chlorpyrifos), and Fortress (chlorethoxyfos). The herbicides include both soil-applied and postemergence herbicides. Some of the common products include Callisto (Halex GT); Resolve (Steadfast, Basis); Accent; Capreno, Sharpen or Kixor. Note that the list is not only Group 2 (or ALS-inhibiting herbicides). If using an organo-phosphate insecticide, a list of herbicides that have potential interactions can be found at https://extension.udel.edu/ag/files/2014/01/CornWeedguide.pdf and go to Table 19.
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.
