No. 3 Article 4/April 20, 2012

Options to Control Corn Plants from the Initial Planting

Last week's below-freezing temperatures damaged some emerged corn across portions of Illinois, and some producers will opt to replant damaged stands. Loss in the initial stand could range from partial to complete, so existing corn plants may need to be controlled before replanting.

Glyphosate is very effective for controlling existing stands of corn hybrids sensitive to glyphosate. Corn replanting can occur immediately after application, but control of existing corn plants could be improved if at least 24 hours elapses between application and replanting. Glyphosate also would control sensitive weeds that might have emerged with the initial stand of corn. Other options to control emerged corn include paraquat and glufosinate (only hybrids sensitive to glufosinate), although previous research with these herbicides has demonstrated that complete control is not always achieved. Performance of these products is often enhanced when applied in combination with atrazine or metribuzin. Paraquat and glufosinate would also control a broad spectrum of emerged weeds.

Glyphosate-resistant corn from a first planting can be controlled with Select Max prior to replanting field corn. The label specifies a rate of 6 fluid ounces per acre for control of glyphosate-resistant field corn up to 12 inches tall. Applications should include NIS and AMS (do not use a COC or MSO in this case), and care must be taken to avoid in-field overlaps or excessive injury to the replanted corn might occur. Glyphosate can be tank-mixed with the Select Max to control emerged broadleaf weed species. Do not replant fields treated in this way sooner than six days after application or severe injury to the replanted corn can occur.

Replanted corn can be injured by soil residues of ACCase-inhibiting herbicides. Be sure to read and follow all label precautions to avoid injury to replanted corn.

The product labels of Poast, Poast Plus, Fusion, Fusilade, Select, and Assure II specify an interval that must elapse between application and rotation to or replanting with grass crops such as corn. These intervals range from 30 days (Poast, Poast Plus, Select) to 60 (Fusion, Fusliade) to as many as 120 (Assure II), making these products unlikely choices for this use. Severe injury to replanted corn can occur if soil residues of any of the ACCase-inhibiting herbicides described here are taken up by the emerging corn plants.--Aaron Hager

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