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Battling a prehistoric weed

Scouringrush has probably been around for some 300 million years. With no leaves and very little branching, it has several names like snake grass, jointed grass, horsetail or horsepipes. Unique and interesting, this hollow green-stemmed prehistoric plant in the horsetail family can become a problem weed when it creeps out of streams, waterways and marshy areas into corn and soybean fields.

At a glance

• Scouringrush has probably been around for 300 million years.

• The prehistoric weed poses more of a problem in stands of soybeans.

• Extension specialists are studying herbicides and application timing.


“We receive calls each year from individuals wondering how to control scouringrush,” says Mark Bernards, University of Nebraska Extension weed specialist. “It is probably a more obvious weed because glyphosate does not kill it, and no-till favors its survival and spread.”

Bernards has been researching control methods for the past four years, compiling data on how well herbicides, tillage and mowing control scouringrush. Next spring, he plans to study herbicide application timing.

“Generally, we find scouringrush in waterways and wet holes,” he says. “But patches can spread into drier areas adjacent to wet spots.”

Bernards says that controlling scouringrush once it’s established is a challenge because the plants are most likely well connected through their extensive system of fibrous roots and rhizomes, which is the primary way the plant produces. “Once it spreads into crop ground, it is an economic problem for that portion of the field, which is usually less than an acre,” he says. “In the patches where we’ve conducted research, it has spread from 1 to 2 yards further out each year.”

The most effective herbicides are not labeled for use in corn or soybeans, and have residual carryover that would stunt those crops the year after treatment. There is one herbicide that is labeled for use in wheat, but to control scouringrush, it requires an application rate several times the rate allowed for use in wheat, Bernards says.

“Scouringrush is not as competitive in a shaded environment,” he says. If a farmer is able to till infested patches before planting and establish the corn crop before the scouringrush recovers, the weed will be stunted or its density will be reduced.

Soybean problem

Bernards says that infestations are more competitive with soybeans. It is able to canopy over soybeans and rob the crop of light to cause its damage. Growing up to 3 feet tall in dense patches of up to 350 stems in 2.5 square feet, it seems to more easily tower above and encompass stands of soybeans.

Now that herbicide trials are completed, Bernards is hoping to find farmer participants with invasive stands next season for more study on the effectiveness of different herbicide applications at specific times in the growth cycle. For plants similar to scouringrush, he says that applications after July 15 work best.

“The reasoning is that these plants put most of their energy into growing the shoot in the first half of the summer, and in the second half most of the energy is transported down to the rhizomes,” he says. “In later summer, more of the herbicide would be translocated to the rhizomes, making the herbicide more effective.”

For more information on participating in field trials or control measures that work on scouringrush in field crops, contact Bernards at 402-472-1534 or visit cropwatch.unl.edu/web/cropwatch/archive?articleId=4169854.

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ENCROACHING Plant: Photo shows a scouringrush patch. The prehistoric plant is moving into fields in parts of the state.

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WELL-CONNECTED Weed: Once established in crop ground, scouringrush is a challenge because plants are connected through fibrous roots and rhizomes. Note the new shoots emerging.

This article published in the September, 2010 edition of NEBRASKA FARMER.

All rights reserved. Copyright Farm Progress Cos. 2010.