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Issue No. 3, Article 9/April 14, 2006

Know What's Planted Where

The adoption of corn hybrids with resistance to various herbicide classes undoubtedly will increase during 2006. These hybrids may offer several advantages for weed management, but farmers should remember there are few silver bullets or cure-alls, if any, for managing weeds. We offer these reminders early in the season with the hope that certain problems (nowadays generally referred to as "opportunities" instead) can be avoided later in the season.

1. Know which hybrid has resistance to which herbicide(s) and where it's planted. In other words, remember to match the herbicide to the herbicide-resistance trait of the particular hybrid in a given field. The three most common herbicide-resistance traits in today's corn hybrids are glyphosate resistance (RR), glufosinate resistance (LL), and imidazolinone resistance (CF). While the names glyphosate and glufosinate may look and perhaps sound similar, the herbicides are dissimilar enough that a farmer will not be pleased should a field of glufosinate-resistant corn be treated with glyphosate, or vice versa. Some corn hybrids are resistant to both glyphosate and glufosinate, but be certain to check the seed-bag tag to know if the hybrid you are planting has resistance to one or both of these herbicides.

2. If you are planting a hybrid with resistance traits for corn rootworm and herbicide(s), take care to record what hybrid is planted as the refuge. For example, if a rootworm/glyphosate-resistant hybrid is planted, will the refuge be planted with a glyphosate-resistant or conventional hybrid? If a glyphosate-resistant hybrid is planted as the refuge, the entire field can be treated with a postemergence application of glyphosate. However, if the refuge is planted with a conventional hybrid and a postemergence herbicide application becomes necessary, a nonglyphosate-containing product must be used.

3. Plan ahead for the control of volunteer herbicide-resistant corn in herbicide-resistant soy bean. For example, if a glyphosate-resistant corn hybrid was planted in a particular field in 2005 and that same field will be planted with a glyphosate-resistant soybean variety in 2006, volunteer glyphosate-resistant corn will not be effectively controlled with glyphosate. Control of volunteer glyphosate-resistant corn in soybean can be achieved with certain soil-applied herbicides or with post-emergence herbicides such as clethodim, quizalofop, and so on.--Aaron Hager and Dawn Nordby

Aaron Hager
Dawn Refsell

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