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Published January 18, 2011, 10:45 AM

Expert says weed killer too vital to lose to resistance

FARGO, N.D. — Australian farmers are No. 1 in the world for weed resistance to herbicides. but the U.S. — because of its overuse of glyphosate — is poised to take that dubious top honor.

By: Mikkel Pates, Agweek

FARGO, N.D. — Australian farmers are No. 1 in the world for weed resistance to herbicides. but the U.S. — because of its overuse of glyphosate — is poised to take that dubious top honor.

U.S. resistance problems are most serious on the “big driver weeds” in the southern Corn and Cotton belts, a world-renowned herbicide resistance expert says. Driver weeds are the weeds that drive farmers’ decisions on when to apply herbicides.

Farmers in eastern North Dakota and northwestern Minnesota’s Red River Valley area already are seeing problems.

Stephen Powles, director of the Western Australian Herbicide Resist-ance and World Grains” (2001), Powles stresses the miracle of glyphosate.

Powles was a featured speaker in a half-day seminar in Fargo, N.D., sponsored by Peterson Farms Seed of Prosper, N.D., and Bayer CropScience. Other area weed scientists have been raising their voices and eyebrows about the path toward weed resistance, but Powles’ accent and international reputation made some 200 crop consultants and a smattering of farmers in the crowd sit up and take notice.

Production demands

Powles started with an overview of the need for increased food production. Briefly: the world adds 216,000 mouths to feed, daily.

“Somebody is going to have to feed these people, and it’s going to be you and I,” he says.

He describes the importance of glyphosate in increasing food production in the “big five” countries of the U.S., Brazil, Australia, Canada and Argentina. He says resistance already threatens Australian grain production, but he predicts the U.S. will become “No. 1 in herbicide resistance.”

He says what’s currently known as the Corn Belt could become known as the “Glyphosate (resistance) Belt.” He says glyphosate “is a 100-year discovery” and that — at as little as $3 an acre — is underappreciated for the miracle it is.

“Anything you can do to keep glyphosate working on your farm, do it,” Powles says. “We are massively overusing this herbicide.”

Glyphosate now accounts for $5.5 billion in the world’s herbicide sales — more than all of the rest when added up. Paraquat is second, at about a half-billion, followed closely by mesotrione. He says if farmers want to keep using glyphosate. they must “start using some of these other ones; in fact, get them in there as quick as possible. You don’t have to have a Ph.D. in biology to realize that’s unsustainable.”

He says farmers can turn to Liberty Link and Ignite technology, to help provide a “rest” for glyphosate, but warned that those are just “part of the solution” and that not a “silver bullet.”

“Herbicide sustainability is all about rotating crops, rotating herbicides, rotating everything else you can think of to make sense,” he says.

Australia’s weed resistance problems are an evolution: 1770s, England’s shipping convicts to Australia; 1850s, the start of the sheep industry in southern Australia, and cultivation of annual ryegrass to feed them; the 1960 and 1970s, the decline of wool and sheep demand; 1970s and 1980s, the shift toward to no-till wheat and advent of Hoelon herbicide, which killed the ryegrass weeds and not the crop. There was the shift to burn-downs, and the use of glyphosate, and the resulting “multiple-resistance” problems.

Maintaining no-till

Powles says he and other Australian farmers want to keep their no-till practices, partly because of rainfall limitations. But some have turned to some mechanical means to destroy weed seed. Most have attached and invented machines for the backs of their combines, where — instead of blowing the chaff and weed seed to the back of the combine — they gather crop residue into hoppers for later destruction or place them into narrow windrows that later are burned.

From the air, Australian grain fields now are streaked with “big black lines,” where the systematic chaff burning is used to reduce the carryover of resistant weed seeds on 15 million acres. He isn’t sure if the fire would be hot enough if it were used in corn residue in the Red River Valley. He says it might have “partial effect,” but adds U.S. farmers likely will come up with new solutions.

Powles acknowledges there are some farmers in Australia who are “going back to cultivation” to solve some of their Roundup Ready weed resistance problems. Some have tried using moldboard plows to bury some seeds deeper into the ground, which “works really well if you do it really well.”

He did not directly answer an audience question about whether it’s wise to make all crops Roundup ready.

“We live in a capitalistic society, don’t we?”

He says manufacturers must do what they need to do to be competitive, and farmers need to make their own decisions.

Timely applications for post-emergence herbicides and complete weed killing are ways to delay resistance woes, but the economics are complicated.

Greg LaPlante, a crop consultant from Wahpeton, N.D., notes farmers delayed glyphosate applications for weeds last year in Richland County, N.D., so they could save application costs on tank-mixing protestants against soybean aphids, which hadn’t yet reached economic thresholds. Consequently, they were trying to kill weeds that had grown tall enough to break the soybean canopy, leading to more problems with water hemp weed resistance. He says there should be interdisciplinary conversations between weed scientists and entomologists and others, so farmers are advised when to “drop out and spray your weeds.”

Additional topics

Other speakers at the seminar:

n Carl Peterson, president of Peterson Farms Seed, says the elite corn hybrids are Roundup Ready. He says seed companies like his won’t be putting more effort into conventional corn vs. Roundup Ready corns unless farmers demand it.

“The best way for somebody like us to go out of business is to produce a bunch of stuff that nobody wants,” Peterson says. “The demand has to be there.”

n Ford Baldwin, owner of Practical Weed Consultants L.L.C. of Austin, Ark., says he advises clients to “get all the firepower you can” out of conventional herbicides and save the glyphosate for the places where it is most needed. He says that tank-mixing partner chemicals has its limits, and only works if the partners have different chemical actions for the same target weeds. He says weed resistance already is causing tense relationships between landowners and renters. He described situations in which farmers have had to go back to hoeing weeds out of crops, and times he’s had to tell producers to simply disk down crops where their herbicide resistance issues have gone unchecked.

Baldwin says the same thing could happen in the Northern Plains, unless farmers become proactive.

“You guys have to prove them wrong,” he says, and implement preventative resistance management — not wait for “firefights” in managing resistance. “We’re in a firefight. You don’t want to go there,” he says.

n Michael Christoffers, an associate professor in weed science and genetics at North Dakota State University in Fargo, says, in this area, farmers are seeing multiple species of weeds surviving glyphosate applications, which could indicate problems are caused by something other than resistance. He says scientists (including Jeff Stachler, an NDSU/University of Minnesota sugar beet weed specialist, who was out of town) are monitoring for glyphosate resistance, and what’s been found so far: common ragweed in Minnesota and North Dakota; water hemp and giant ragweed in Minnesota; lambsquarters may be resistant in Minnesota and North Dakota, though there is a lot of variability. Multiple applications control most of the plants so far. Kochia may be resistant in North Dakota. In greenhouse experiments at NDSU, kochia plants have survived. glyphosate at twice the rate of susceptible plants, but at less than a normal rate.

Christoffers says farmers need to scout for resistance, but often can “convince themselves” that something else is wrong — dust or near field rows.

“Those conditions that gave you less-than-desirable weed control may be what is revealing low-level resistance,” he says.

n Virgil Jons, owner of Agassiz Crop Consulting of Moorhead, Minn., says he’d like growers to choose their most important economic crop — whether it’s sugar beets, corn or soybeans — and focus on keeping that protected by glyphosate (assuming Roundup Ready sugar beets eventually may be made legal) and looking for alternative chemistry to protect rotation crops. Jons, who does crop consulting for 16 clients in Cass County in North Dakota and Clay County in Minnesota, says corn has better alternative herbicides, and he personally doesn’t see the need for Roundup ready wheat at all.

“I just hope it never shows up in wheat,” he says.

He says alternative chemistry doesn’t work as well in sugar beets. He says he’d like to see farmers drop at least one of their rotated crops out of Roundup ready technology because it adds to Roundup resistant selection pressure.

n Gary Johnson, with McIntyre-Pyle Inc., a farming and agribusiness operation in Casselton, N.D., told how his farm purchased some Cass County land that had been planted to Roundup Ready soybeans continuously for more than a decade, and had Roundup-resistant common ragweed. Part of the land had had corn the previous year and they didn’t get the crop off in time, so they put soybeans on it. When the ragweed showed up, they tried to control it with glyphosate and on a test plot tried it with three times the normal rate, also without effect. To rid the field of the resistant weeds he planted to wheat in 2010, and plans sugar beets in 2011, wheat in 2012 and corn in 2013 before perhaps shifting it back to soybeans after that. Johnson specializes in conventional, non-GMO soybeans for export food markets.