Purdue News

September 27, 2006

Specialist: Fall herbicide applications weed out winter annuals

WEST LAFAYETTE, Ind. — As combines roll through corn and soybean fields this fall, spraying equipment might be close behind.

Fall herbicide applications are becoming more common as farmers attempt to stop winter annual weeds from gaining a foothold the following spring, said Glenn Nice, a Purdue University Extension weed scientist.

"One big reason fall applications are gaining momentum is the adoption of no-till systems," Nice said. "In a no-till system it is a bad idea to plant directly into a bed of weeds, so you either have to consider a burndown application in the spring or a fall herbicide application.

"Winter annual weeds have become more an object of concern because we've had some mild winters in recent years. This makes it easier for winter annuals to survive. So in the spring we wind up with a fairly good mat of chickweed, henbit and purple deadnettle when we get ready to plant."

Another winter annual causing problems is cress leaf groundsel, commonly known as butterweed. The bright yellow weed spreads rapidly and can slow a field's ability to dry in the spring. Fall-applied herbicides are more effective in controlling cress leaf groundsel than burndown applications, Nice said.

"In the fall, cress leaf groundsel is a rosette," he said. "In the rosette stage it is far more susceptible to herbicides."

Farmers considering fall herbicide applications should be aware of both the pros and cons of the weed management strategy, Nice said.

"One of the pros of using a fall-applied herbicide system is that you have a clean seedbed in the spring," Nice said. "If the winter cooperates, you might even be able to plant without having to worry about making a burndown application in the spring.

"Another advantage to fall-applied systems is the planting window the following spring. The past several years we've been having fairly wet springs, thus pushing us out of the field for longer periods of time. This allows a lot of the weeds to build up and germinate in the early spring. A fall-applied herbicide with some residual activity can increase the window of when you would have to be in the field to plant."

Fall herbicide programs aren't for everyone, however, Nice said.

"If you're in a highly erodible area, it's probably a good idea to leave some vegetation on the field over the winter to reduce the movement of topsoil," he said. "Also, if the winter does not cooperate with you, you may still have to put down a burndown application anyway.

"One other thing to keep in mind is that a lot of your fall-applied systems would not control giant ragweed in the spring. Often, if you use a product that does not have any residual activity, you're still going to get germination of lambsquarter and chickweed and so forth. Even with a residual there's a good possibility that the residual activity will not be present at the time that giant ragweed starts to germinate."

For more information about fall herbicide applications and a list of products labeled for use in Indiana, read "Fall Applied Herbicides for Corn and Soybean in 2006," by Nice and fellow Purdue weed scientist Bill Johnson. The article appeared in the Sept. 22 issue of the Purdue Pest and Crop Newsletter. The newsletter is available online.

Additional weed management tips can be found on the Purdue Weed Science home page.

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

Sources: Glenn Nice, (765) 496-2121, gnice@purdue.edu

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

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

Note to Journalists: Other farm-related story ideas are available at Purdue Agriculture's Farming 2006 Web site

Related Web site:
Purdue Department of Botany and Plant Pathology


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