October 23, 2007

Booklet tackles uncommonly resilient common lambsquarters

"Biology and Management of Common Lambsquarters" is the seventh in a series of publications on weeds that are developing resistance to glyphosate - the main ingredient in the popular herbicide Roundup. The booklets are produced by Purdue University weed scientists and their colleagues at 15 other universities that make up the Glyphosate, Weeds and Crops Group.

"This new publication discusses the biology of the weed, the factors that make it difficult to control with glyphosate and some of the management tactics that we would like to see growers employ in order to get effective management of common lambsquarters," said Bill Johnson, Purdue Extension weed scientist and a member of the publication development team.

A summer annual weed, common lambsquarters can cause yield losses in both corn and soybeans, although the weed is a bigger problem in soybeans, Johnson said. No glyphosate-resistant populations have been confirmed in Indiana, but there have been cases of lambsquarters resistant to aceto-lactase synthase (ALS) inhibitors. ALS inhibitors kill weeds in much the same way as glyphosate - by preventing them from producing essential amino acids necessary for growth.

"Four out of the last five years we've had widespread instances of lambsquarters control failure in our soybean fields," Johnson said. "We feel that this weed is one of our more competitive weeds and very difficult to control with almost any postemergence herbicide, including glyphosate.

"Common lambsquarters has developed resistance to ALS inhibitors and triazine herbicides. Triazine resistance is widespread in the eastern part of Indiana. Many of our growers there no longer rely on triazine herbicides to provide effective control of common lambsquarters, and they are forced to go with other herbicide modes of action. ALS-resistant lambsquarters are probably somewhat scattered throughout the state but certainly are present in Michigan, Ohio, Illinois and throughout the Midwest."

Lambsquarters is troublesome because it grows rapidly during the early part of the crop season and can remain viable when crops are mature, Johnson said.

"Yield losses in patches of heavy lambsquarters infestation can be 30 to 50 percent," he said. "The other problem that lambsquarters causes is that if a person is trying to harvest their soybeans before a frost, the weed remains green very late into the growing season and can plug up harvesting equipment and also put trash into the grain."

Farmers attempting to keep common lambsquarters at bay must implement a proactive control program, Johnson said.

"It's imperative that growers with lambsquarters problems start with a clean field," he said. "If they are no-till producers, they need to have 2,4-D in with their burndown program, particularly if they've got a lambsquarters population that's tolerant to glyphosate.

"The best thing that we can do for lambsquarters control is use soil-applied herbicides. Almost every soil-applied herbicide that we use in corn and soybeans has some activity on lambsquarters."

"Biology and Management of Common Lambsquarters," Extension publication GWC-11, can be downloaded at the Glyphosate, Weeds and Crops Web site at https://www.glyphosateweedscrops.org.

Other publications in the series include:

* "Facts About Glyphosate-Resistant Weeds"

* "Understanding Glyphosate to Increase Performance"

* "Biology and Management of Horseweed"

* "Biology and Management of Wild Buckwheat"

* "Biology and Management of Giant Ragweed"

* "Corn and Soybean Herbicide Mode of Action Chart"

Future publications will cover glyphosate-resistance in common ragweed and common waterhemp, and the economics of glyphosate stewardship.

The publications are produced with financial support from herbicide manufacturers and commodity groups.

For additional information about weed management, visit the Purdue Weed Science Web site at https://www.btny.purdue.edu/weedscience/

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: Bill Johnson, (765) 494-4656, wgj@purdue.edu

Ag Communications: (765) 494-2722;
Beth Forbes, forbes@purdue.edu
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