Several factors may delay postemergence herbicide applications. When this happens it is important to be aware of restrictions on the label based on corn size or growth stage, says Iowa State University Extension weed management specialist Bob Hartzler. The reasons for these restrictions vary among products, but may involve crop tolerance and prevention of residues in soil or grain. When making application to fields that received frost damage, remember to consider the number of leaves lost to frost.
Another consideration with delayed applications is the size of weeds, says Hartzler. The likelihood of the herbicide providing control of weeds larger than specified on the label should be considered.
Several products allow applications to larger corn if a directed application is made. In these situations the sprayer needs to be set up so that nozzles direct the spray between the corn rows to minimize the amount of spray interacted by the crop and to improve coverage of weeds.