A potential scenario encountered each growing season is corn planted in fields where no soil-residual herbicide was applied. If the corn has not yet emerged, the soil-residual herbicide can be applied as originally planned. But, what if the corn has emerged and the soil-residual herbicide has not been applied? Can the application proceed as planned, or will a different product need to be selected? The answer depends on the respective herbicide.
Most, but not all, soil residual herbicides can be applied after corn has emerged. Products such as Prequel, Sharpen and Verdict must be applied before corn begins to emerge; applications of these products to emerged corn can result in significant corn injury. Be cautious about applying a soil-residual herbicide in UAN carrier if corn has emerged as this can increase the potential for corn injury.
Several soil-residual herbicides can control small, emerged summer annual weeds. Additional management procedures (such as the addition of a herbicide that has postemergence activity) will be needed for those products that lack the ability to control emerged weeds. Be sure to consult the respective product label for tankmix and additive recommendations.
Herbicide labels (Table 1) usually indicate a maximum corn growth stage beyond which applications should not occur. These growth stages can range from as early as two leaf collars to as late as 40-inch tall corn, so be sure to consult the respective product labels. Products containing atrazine must be applied before corn exceeds 12-inches tall, although the labels of some atrazine-containing products specify a shorter height. If labels include restrictions based either on corn height or corn growth stage, be sure to follow the more restrictive of the two.