Due to late planting, and then wet, cool weather last week, some farmers were unable to apply a pre-emergence herbicide to corn. The University of Nebraska-Lincoln has some tips for applying a residual herbicide after corn emergence, including reminding growers to not apply herbicide with nitrogen, There is also a chart with corn stages, weed growth and the appropriate herbicides to apply.
Application of soil residual herbicides is important because usually they deliver several weeks of weed control, cover a broad spectrum of weeds, and aid in weed resistance management by incorporating additional site(s) of action. Several residual, pre-emergence herbicides such as Breakfree, Dual II Magnum, Harness, Keystone, Prowl H2O, Warrant, Zidua can be applied after corn emergence without injury to corn.
Attempting to save a trip across the field by applying an herbicide with a liquid nitrogen fertilizer solution, such as 28% urea ammonium nitrate (UAN), as the carrier is not advisable if corn has emerged. (SeeCropWatch article.) Tank-mix partners may cause other effects regardless of the application timing. Follow application timing and other restrictions of tank-mix herbicide partners as noted in the herbicide label.
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