FOCUS ON AGRICULTURE: Waterhemp control requires changing mindset

Posted: Jan. 30, 2013 1:55 pm Updated: Feb. 28, 2013 9:15 am


In the war between waterhemp and producers, waterhemp is winning, and the problems go far beyond glyphosate resistance.

"If you've just got glyphosate-resistant waterhemp, you should consider yourself lucky," said Kevin Bradley, University of Missouri Extension state weed scientist. "We're seeing waterhemp with multiple resistance to all the other herbicides that we would use to control glyphosate-resistant waterhemp, so we have fewer options and it is much more costly to control."

When it comes to weed control, a different mindset is needed, Bradley said. Producers no longer can rely on the simplicity of a glyphosate system.

Controlling waterhemp will require more proactive management, spraying much smaller weeds and rotating to herbicides with different modes of action.

Bradley said understanding the biology of waterhemp and identifying its strengths and weaknesses are important.

Its strengths are formidable: Waterhemp produces on average 300,000 seeds per plant, grows an inch and a half a day during the height of the growing season and has evolved resistance to just about every herbicide ever sprayed on it.

More important, though, are its weaknesses. "Waterhemp seed is relatively short-lived in the soil -- four or five years. If you've kept waterhemp from producing seed and returning seed back onto that land for four years, you are probably going to virtually eliminate waterhemp from your fields," he said.

Waterhemp seed also does not emerge from low soil depths. Bradley doesn't recommend it to every grower in every place, but where appropriate, deep tillage can bury that seed and it will not come up.

"In addition to understanding the biology of waterhemp, if we can rotate to multiple modes of action, I think we can really get a handle on this problem," Bradley said.

More information is available in the MU Extension publication "Management of Glyphosate-Resistant Waterhemp in Corn and Soybean" online at


Name that weed

University of Missouri Extension has released a free app for iPhones, iPads and Android devices to help people easily identify weeds in the field, lawn or garden.

The app, called ID Weeds, has information on more than 400 plant species that could be encountered in Missouri and surrounding states.

ID Weeds lets users narrow the list of suspects with a series of drop-down boxes for various plant characteristics. Clicking on "Identify" will produce a list of weeds that match the characteristics chosen. The more characteristics specified, the shorter the list will be. Selecting a weed on the list brings up detailed information and one or more photographs.

Users also can look up a weed by searching for its common or scientific name, or select from an alphabetical list from "alligatorweed" to "yucca."

Download the app for iPhone and other iOS devices at or for Android by searching for "ID Weeds" at A web version of the app is available at

Compiled by Herald-Whig Staff Writer Deborah Gertz Husar.