Source: Iowa State University
Several factors may delay post-emergence herbicide applications, according to Bob Hartzler, Iowa State University. When this happens it is important to be aware of restrictions on the label based on corn size or growth stage. 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. The likelihood of the herbicide providing control of weeds larger than specified on the label should be considered.