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Corn+Soybean Digest

Hit Woolly Cupgrass Three Times

An aggressive triple whammy of control measures is usually needed to rid cornfields of woolly cupgrass.

Mike Leetch, a technical service representative with Zeneca Ag Products, advises growers to attack the weed with a pre-emergence application of an acetochlor herbicide. Harness and Surpass are recommended by Bob Hartzler, Iowa State University extension weed scientist.

Follow that treatment with a mechanical control method, such as rotary hoeing or cultivation. Finally, a postemergence grass herbicide, such as Accent, should be applied, says Leetch.

A diverse management plan is critical for woolly cupgrass control, concurs Hartzler.

"One of the biological characteristics of woolly cupgrass is that it will germinate for an eight- to 10-week period during the summer," says Leetch. "Unfortunately, pre-emergence corn herbicides don't last long enough to control July and August woolly cupgrass escapes."

Woolly cupgrass is most troublesome in corn, so rotation to alfalfa or soybeans is often helpful.

In soybeans, postemergence grass herbicides, such as Fusion, Select, Poast Plus and Assure II, do a good job on it, says Leetch.

The weed is often confused with giant foxtail; however, it typically emerges earlier.

"The most common way to tell the difference between the two weeds is to look at the leaf margin of the woolly cupgrass, which is rippled or wavy on one side. In its earliest stage of growth as a seedling, the first two leaves that emerge on the cupgrass plant are very wide and very flat," he says.

The weed has been gaining ground in Iowa, southern Minnesota, southern Wisconsin and parts of Illinois for the past decade. It's also creeping into South Dakota and Nebraska.

University of Minnesota and Iowa State weed scientists attribute that rise to several factors:

* Woolly cupgrass has a higher level of tolerance to most postemergence herbicides than other grass species.

* It germinates over a wider range of soil temperatures and depths, resulting in numerous flushes throughout the growing season.

"Woolly cupgrass will germinate in dry or wet soil, in warm or cool weather and from the surface to as deep as six inches," says Leetch.

* Seedlings begin tillering at the two- or three-leaf stage.

* A single plant is capable of producing about 170,000 seeds, so any plants that escape control quickly replenish the seed bank.

"Woolly cupgrass seed can survive in the soil for up to five years," says Leetch. "If it doesn't germinate this year, you could find it several years from now."

Growers who plant herbicide-tolerant corn have more postemergence control options: Poast on sethoxydim-resistant (Poast Protected) corn; Lightning on imidazolinone-resistant (IMI) corn; and Roundup Ultra on Roundup Ready corn.

"However, a pre-emergence application of an acetochlor herbicide and rotary hoeing or cultivation is still vital for cupgrass control in herbicide-tolerant corn," says Leetch.

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