Weed Control Challenges Corn Growers This Spring

PRINCETON, KY.

 Because of the wet spring, corn planting has been sporadic and delayed. These conditions have created some unique challenges in regards to managing weeds. In some cases corn growers were able to plant several acres before a significant amount of rain but failed to apply a soil-residual herbicide before corn emerged. The fact that many of the soil-residual herbicides can applied be overtop emerged corn allows some flexibility application timing to corn. However, some soilresidual herbicides do not control emerged weeds, especially weedy grasses, consequently it may be necessary to include a selective postemergence herbicide with a soil-residual herbicide.

    Flooding of low-lying portions of fields caused poor stands of corn but did not affect stands in other areas of the field. Growers have attempted to replant the areas where stands were unacceptable but encountered difficulty in controlling scattered surviving corn in the low lying areas. If the original stand is not glyphosate-tolerant, then glyphosate would be an effective option for controlling emerged corn before replanting back to corn. However, if the original stand is tolerant to glyphosate, then one alternative would be to use a tank mix of paraquat plus Linex (linuron). Ideally corn plants should have at least two to three leaves with collars (the white band where the leaf blade connects with the leaf sheath). Select Max is another burndown option to control unwanted corn plants, but it requires a minimum waiting period of 6 days before replanting corn.

   Replanting only selected areas will likely result in a significant difference in growth of corn in the original planting compared with corn in the replanted areas. The difference in growth from the two plantings may make it difficult for timing of postemergence herbicides in order to achieve optimum weed control and not injure the crop. Try to select options compatible for the different growth stages of corn. Depending on the situation, it may be necessary to manage each planting separately.

   Because of the significant delay in planting corn, some growers may want to switch from corn to another crop such as grain sorghum or soybean. If a soil-residual herbicide was applied, consult the label to determine what replant options are available. If atrazine was applied, then grain sorghum would be a safer option compared with soybean. Δ.