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Avoid crop damage when spraying frost-damaged corn

Agriculture.com Staff 05/17/2010 @ 8:39am

If your corn got nipped by frost earlier this month, make sure you're not doing more harm than good when you go put down herbicide.

Many product labels use plant height or leaf number for the basis for application. But, leaf damage is typical when plants are hit by frost, meaning those plants often appear less developed than they really are, says Iowa State University Extension agronomist Bob Hartzler.

"For many herbicides, application restrictions on the product label are based on factors other than corn developmental stages and injury potential," Hartzler says. "Thus, misjudging the corn's stage of development should not increase the potential for injury in those cases."

That can make it tough to tell whether or not your plants have reached the stage where they can be treated.

"Assume that a field is staged on May 29 and has four visible leaf collars. Normally, you'd call this a V4 plant. However, if this field was planted in mid-April and on May 9 had two emerged leaves that were killed by frost, the actual developmental stage would be V6 rather than V4," Hartzler says. "With careful examination it might be possible to find remnants of the frosted leaves, but in many cases they will not be present. If staging the corn by height, the same problem of underestimating the stage of development exists."

This makes it even more important than usual to pay close attention to the label for whatever product you're applying, as some have more potential to damage frost-nipped plants than others.

"The main concern will be with herbicides for which application restrictions are based on crop tolerance concerns. For example, many sulfonylurea herbicides prohibit broadcast applications beyond the V6 (6 collar) stage," Hartzler adds. "This restriction is present because applications made later than this may damage the ear since it is initiated at this time. The growth regulator herbicides and Ignite also have application timing restrictions based on crop injury risk."

Double-check any potential crop damage and tolerance issues with your herbicide representative, Hartzler recommends. And, make sure you have documented each field's frost damage for reference later on in the season.

"Consider this information when determining the appropriate time for application," he adds.

If your corn got nipped by frost earlier this month, make sure you're not doing more harm than good when you go put down herbicide.

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