November 3, 2011
This relative of pigweed, waterhemp, which resembles redroot pigweed in the early growth stages, is now a problem in parts of Indiana, particularly central and southern Indiana. Once upon a time it was a weed that we mentioned only because it was a problem for farmers in neighboring states.
Not only has waterhemp taken up residence in Indiana, but glyphosate-resistant waterhemp is now documented in Indiana. Betsy Bower, an agronomist for Ceres Solutions, Terre Haute, says a field of resistant waterhemp was confirmed in Vigo County even before this season.
That doesn't mean that every field where waterhemp was a problem in 2011 had resistant waterhemp, Bower is quick to notes. Sometimes the weed in that field isn't resistant. Instead, other factors, including environmental conditions and management methods, allow the weed to escape. It has nothing to do with resistance.
There is a lab at Purdue University that can grow out the seeds and test to see if a sample you send in is actually resistant. Contact your county Extension educator if you want to submit suspicious plant to Purdue for testing to see whether or not you have resistant waterhemp on your farm.
You may also be looking at maretails, sometimes called horseweed. It's another one that could be tied to changes in weed control methods. There are resistant marestail to glyphosate in Indiana. At the same time, Bower notes that not every field that has a dominant problem is beset with the weed because it is resistant to glyphosate.
If you have waterhemp, especially resistant waterhemp, it can be controlled more easily in corn than in soybeans. However, there are herbicides in both crops that will control it. Look for detailed descriptions of possible control options for waterhemp in the December edition of Indiana Prairie Farmer magazine.
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