FAIRMOUNT, N.D. -- Crop advisors and weed specialists say waterhemp has moved another 30 miles farther north in the Red River Valley, and a well-known agronomist says farmers have only a few days or weeks to control herbicide-resistant weeds.

Greg LaPlante, owner of GL Crop Consulting of Wahpeton, N.D., is issuing a "call to action" for farmers to address weed issues this fall. LaPlante has a number of clients near the Bois de Sioux River, which becomes the Red River at the adjacent towns of Wahpeton and Breckenridge, Minn.

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LaPlante, a 33-year veteran in the field, says farmers now have only a few days to mow down or control weeds in field ditches and road ditches as soon as possible. He's most concerned-- waterhemp, but also common ragweed, marestail  and others that are becoming resistant to glyphosate and other herbicides.

On a recent field visit to LaMars Township, between Hankinson and Fairmount, LaPlante pointed out a progression of waterhemp resistance ranging from manageable to "out of control" fields, with weeds 11 feet tall, rising above standing corn. Waterhemp is difficult to control because it emerges over a long period of time, with some weeds still emerging at the end of August -- after the pre-emerge herbicides have worn off.

LaPlante estimates that the 900-acre size of the watershed at this point -- where the Bois des Sioux Valley is only two or three miles wide -- could probably produce enough herbicide-resistant weed seed to infest every field along the Red River to Fargo. "If we get a big snowfall winter and we have a lot of water moving north out of some of these fields, it's going to be magnified ten times what it was a few years ago, when we had the last big floods," LaPlante says.

"A lot of our pre-emerge or 'lay-by' herbicide (applications) have run out by (August)," LaPlante says. "Because we don't control the weeds in our soybean rotations, the weed can  overwhelm our corn crop. When that happens you can see 30 to 50 percent reduction in yields as well as impairing your ability to harvest in either crop."

Insidious damage

Some of the first waterhemp plants that emerged this season have already produced mature seed that will be carried to neighbors in the next floodwaters. Others is just in the process of pollinating and setting seed. "We don't have enough hand labor in this area to do a walk-through to control those weeds," LaPlante says. "They need to be mowed." The situation is urgent enough, where farmers should simply cut down the outside row of corn "for their own benefit, just to mow down their seeds," he says.

LaPlante says farmers often shift to LibertyLink soybeans -- genetically modified to be tolerant to glufosinate herbicide -- if their weeds are becoming resistant to Roundup. "Liberty is not as Roundup was," LaPlante says, adding, "If we have millions of seeds per acre, we can overload the Liberty system pretty fast." Some farmers using LibertyLink will have to pre-emerge herbicides along with the Liberty to control resistance.

If the weeds aren't controlled in the corn and soybean rotations, farmers will have more trouble controlling them in higher-valued, niche crops like dry edible beans, sugar beets and sunflowers. "Our options become much more limited when we don't have a livestock industry to feed forages to," LaPlante says. "If we had a vibrant livestock industry we would have other rotational opportunities." A corn crop could be chopped for silage, for example, which would also control a weed before it went to seed.

Checklist needed

LaPlante estimates that over 80 percent of soybean fields have slight to moderate Roundup resistance pressure in Wilkin County in Minnesota, Roberts County in South Dakota and Richland County in North Dakota. Some farmers have told LaPlante they "don't know" if they have a weed resistance problem because it hasn't been confirmed by some expert.

"We need to almost develop a checklist: how do you identify whether these weeds are resistant," he says.

LaPlante says growers aren't coming to industry and North Dakota State University Extension Service and seminars including the Wide World of Weeds in January. Most attendees are crop consultants, so far. He adds that lenders need to be educated about how seriously weed resistance can affect expected returns from cash rent.

"I think growers need to realize that herbicide-resistant weeds could be the problem that could put them out of business in the next several years," LaPlante says. "It's happened in Arkansas. If you start adding $30 to $40 per acre in controlling weeds, plus the lost yield, a farmer can go underwater (financially) pretty darned quickly."

Once a weed is resistant to a herbicide, all of its offspring will always be resistant to that herbicide, LaPlante says. If the population builds resistance to a second or third herbicide, those offspring are then resistant to all three modes. "That doesn't go away," he says. "The only chance you have is to deplete that seed source to get control of it," he says.

Weeds get in the way of the combine header, and get wrapped up on the rollers. On soybeans, some farmers with heavy infestations may have to wait until a heavy freeze because the waterhemp stays green longer than the crop.

Reports at Grafton

Tom Peters, a North Dakota State University and University of Minnesota weed specialist for sugar beets, is seeing waterhemp along the Red River east of Grafton, N.D.

"It just keeps moving north!" says Peters, who was the subject of an Agweek cover story on Aug. 3, when he reported waterhemp had spread 60 miles to the north to Highway 2 area at Grand Forks. Grafton is another 30 miles north.

"I walked along the Red River in a field adjacent to the Red River near state road, 17, east of Grafton, N.D., and positively identified it," Peters wrote in a recent online report. "Our idea is waterhemp probably moved north in river water and found agricultural fields during spring flooding."

Peters noted Shawn Kasprick, an agronomist with Simplot, who speculates the plants near the river may have been the result of flooding in 2013. Peters says farmers need to vigilantly scout and positively identify the weeds. Waterhemp is easy to identify once it gets larger and begins to flower. Waterhemp stem and leaves are smooth and contain no hairs. Flowering can also differentiate it from redroot pigweed, Powell's amaranth and smooth pigweed. For an on-line guide, go to https://www.bookstore.ksre.ksu.edu/pubs/S80.pdf.

 

CHECKLIST

Among the things crop consultant Greg LaPlante of Wahpeton, N.D., says farmers should do to control herbicide-resistant weeds:

1) When soybeans are full-grown, make a mental note and write down which fields have the worst weed pressure, and where.

2) Study the weed seed loads in their fields to manage seed inventories over several years. Kochia weed seed, for example, might degrade and become unviable in two or three years, while waterhemp, redroot pigweed, and lambsquarters have harder seed coats and might remain viable for five to 10 years.

3) Put a small grain crop in the rotation one year out of four. It offers herbicide options that don't exist in genetically-modified crops.