The prolonged period of rain and high winds has prevented timely application of postemergence herbicides in many fields. By the time conditions allow field work, corn may be beyond the optimum size for postemergence applications. There are several concerns with delayed applications, including: 1) label restrictions regarding crop or weed size, 2) increased sensitivity of large corn to herbicides, and 3) reduced efficacy due to large weed size and/or canopy interference with spray coverage.

The following tables list the maximum corn size specified on herbicide labels. As corn increases in size, the crop canopy intercepts a significant portion of the herbicide spray. This may reduce performance due to inadequate coverage of weeds or enhance the potential for crop injury. Drop nozzles will reduce these risks by directing the spray to the weeds, therefore improving coverage and reducing corn exposure.

Table 1. Application restrictions for postemergence grass control in conventional corn.

¹Use most restrictive measurement.

Table 2. Application restrictions for postemergence broadleaf control in conventional corn.

¹Use most restrictive measurement.

Table 3. Application restrictions for herbicide resistant corn hybrids.

¹Use most restrictive measurement.