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Rescuing fields from waterhempRescuing fields from waterhemp

If waterhemp escapes and gets big, don’t waste money trying to spray it with a herbicide.

May 21, 2018

2 Min Read
TOO BIG TO SPRAY: As waterhemp gets larger, it can’t be killed easily with herbicide. Other measures are required.Willie Vogt

What should you do if you don’t get waterhemp controlled and the escapes get big?

Tom Peters, North Dakota State University and University of Minnesota Extension sugarbeet agronomist, provides the following advice:

“Don’t even think about trying to rescue it with herbicides,” he says. “Herbicides are designed to control small, actively growing weeds. Herbicide must contact or translocate to the growing point(s) to effectively kill the weed. Failure of the herbicide to reach each the growing point will result in regrowth from that point on the plant. I have counted nine growing points on a 3-inch waterhemp. A 6-inch waterhemp may have double that number. I can only imagine the number on waterhemp escapes that are 24 to 30 inches tall.

“Hand pulling escapes is an option A few waterhemp plants do not rob yield. Research at the University of Missouri found that at densities of less than 10 plants per square foot, yields were reduced by only 1% when waterhemp was controlled at the 6-inch height. However, waterhemp is a prolific producer of seed, capable of producing greater than 500,000 seeds per plant. Waterhemp robs yield following a herbicide failure and once it has become established in fields. Pulling and bagging waterhemp is challenging work but it is a way of preventing further seed production in a field. Harvest bigger plants first if you must make choices since bigger plants make more seed.

“It may be necessary under certain situations to mow crop and weeds to prevent seed production, especially in an area too large to hand-weed. Waterhemp is most problematic along ditches or in drowned-out areas of the field. Waterhemp must be mowed multiple times since it will attempt to produce a seed head from a growing point low on the stem, even after mowing in late July or August.

“The combine will distribute waterhemp seed across the field. The combine also may move seed from field-to-field. However, cleaning a combine can easily take 4-6 hours, and it doesn’t ensure all weed seed will be removed. One way to reduce the impact of weed escapes is harvest order. That is, harvesting weed-free fields first and harvesting weedy fields last. In addition, be careful to harvest the cleaner portions of weedy fields first and leave heavily infested areas of fields for last.”

Source: NDSU Crop and Pest Report

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