Monday, April 30, 2012

Tense Future: Turning Point in the Battle Against Glyphosate-Resistant Weeds

AgWeek: This year could be a significant turning point in the battle against glyphosate-resistant weeds in the Red River Valley, Jeff Stachler says.

FARGO, N.D. — This year could be a significant turning point in the battle against glyphosate-resistant weeds in the Red River Valley, Jeff Stachler says.

“It needs to be a turning point for the valley and should be for the rest of the state,” says Stachler, extension service sugar beet weed specialist for North Dakota State University and the University of Minnesota.

Stachler is one of the region’s prophets on glyphosate resistance. He’s been trying to get farmers to think beyond their current situations and guard against resistance that their farms don’t yet have. The issue is important for everybody, but more money is at stake for growers of higher-value sugar beets. Beet growers have been planting Roundup Ready seed under conditional approval protocols and are still in a legal struggle to gain permanent approval.

Stachler and others are tracking the incidence of glyphosate-resistant waterhemp, which has moved farther north in the Red River Valley — as far north as southern Traill County in North Dakota, and across the river in southern Polk County in Minnesota.

Stachler says farmers may be awakening to the fact that glyphosate resistance isn’t just down south somewhere — in Richland County, N.D., or west-central Minnesota. Dozens of consultants and others have visited his greenhouse in recent weeks to see the results of his latest research.

“Glyphosate-resistant waterhemp is present in all of southern Minnesota, and the Red River Valley up to Nielsville (Minn.). It’s for sure in Ransom, Richland, Cass, Traill counties in North Dakota,” Stachler says. “And the kochia resistance out west is something we’re not ready for.”

Meeting resistance

Stachler and a colleague, Kirk Howatt, who is working on kochia, have been accumulating evidence of the increase in frequency of resistance in their NDSU greenhouses.

In some cases, Stachler has happened upon resistant waterhemp infestations in his travels and crop consultants and others have alerted him to locales. The researchers collect plants in late September and October, and then cleaned them of seeds that are used for later grow-outs and testing in a greenhouse.

Last fall, Stachler collected waterhemp weeds from Holloway, Minn., (east of Milbank, S.D., in Swift County, Minn.) north to Nielsville, Minn., and Galesburg, N.D. Holloway is a known “hotspot” of glyphosate-resistant waterhemp, starting back in 2008.

His greenhouse weed specimen container sets start with untreated “check populations,” with white tags.

Then there are yellow tags, regular rate glyphosate (0.75 pounds of acid equivalent of glyphosate: 22 ounces of Roundup PowerMax, or 32 ounces of a 3-pound acid equivalent per gallon in a generic product). Finally, there are 3X — three times normal — treatments, with pink tags.

One sample set is from Renville County, Minn., where resistant waterhemp was detected in 2007. Today, collections from the Holloway area in 2010 and 2011 show at least 90 percent of the fields in a five- to 10-square-mile radius likely have “some frequency” of glyphosate-resistant waterhemp, Stachler says. Some 20 percent of the acreage in that area would lose some crop yield if the farmers only sprayed glyphosate.

“That’s not much, but the frequency is so great in that geography, and we’re starting to use other herbicides with glyphosate and if we don’t do it right, we’re starting to select for multiple resistance,” he says, adding, “It’s almost to the point of, ‘Who cares if it’s glyphosate resistance’ versus some other kind of resistance. The question is, is it multiple resistance, and how am I going to manage it?”

In a second case from Holloway, the landowner didn’t use a pre-emergence herbicide and planted Roundup Ready soybeans in 2011 and used glyphosate. “He realized they weren’t going to die, so these plants survived when Cobra was used,” Stachler says. “We have confirmed this to have multiple resistance. This is the greatest resistance to the protoporphyrinogen oxidase (PPO) inhibiting herbicide in Minnesota we’re aware of at this time.”

Today there are resistant waterhemp populations in Clay, Traverse and Wilkin counties of Minnesota (see map on page 28).

Suspecting, knowing

Stachler confirmed glyphosate-resistant waterhemp in Richland County in 2010 for the first time. A population in the Barney, N.D., area has the highest level of resistance seen to date.

Farther north, samples collected in 2010 in southern Cass County couldn’t be proven to have glyphosate resistance in 2010, but did in 2011. Plants exposed to 3X didn’t survive as well as they did in Richland County, but with 1X treatments, the plants survived better than the nontreated check plants. “We know that if we put really low doses of certain herbicides on plants it can actually stimulate growth,” Stachler says. “Our assumption is that the level of resistance is so high that the dosage stimulated the plant growth.”

Before 2011, there was almost no waterhemp west of Kindred, N.D., — either resistant or susceptible to glyphosate. That changed after the 2011 flood, when the Sheyenne River spilled over its banks.

“We all as an agricultural community need to communicate to the scientists what we’re seeing,” Stachler says. “If something is happening on a single grower’s field it’s not likely to stay there, especially if we have significant water movement.”

Stachler says he found out at the end of 2011 that a chemical dealer had trouble controlling waterhemp in soybeans for a farmer in the McLeod area in 2010. That would have been good to know earlier.

A long-term consultant has told Stachler he never saw, or was concerned about managing waterhemp in fields along Interstate 94 in the Mapleton, N.D., area until 2011. “Worse yet, he had plants survive glyphosate,” Stachler says.

Northern exposure

Farther north in the Galesburg, N.D., area, resistance is peculiar because it is on the western edge of the Red River Valley, outside of where flood waters reached.

“Yet, this is the first time I’ve seen a waterhemp population respond (be resistant) so uniformly in an area where we didn’t know we had resistance to glyphosate,” Stachler says. “Unfortunately, the field also had a boatload of common ragweed surviving in it. We know water can move giant ragweed, but I don’t know how well it moves common ragweed.”

Stachler was surprised that weed collections from Minnesota in the Halstad and Nielsville areas, which he expected to be resistant because of floodwater movement, were not as resistant as anticipated from the 2011 crop. “We’re not seeing the same level and frequency of resistance in that area, where water moved the seeds, compared to what we have in Traill County,” he says.

Stachler encourages sugar beet growers to use Liberty Link soybeans because Liberty is an alternative mode of chemistry that, so far, displays no resistance to broadleaf weed species. Stachler doesn’t have hard numbers, but based on conversations, estimates from Fargo, N.D., and south, a significant percentage — perhaps maybe 30 to 50 percent — of sugar beet growers have shifted to Liberty Link beans.

Meanwhile, NDSU’s Howatt has found greater-than-expected glyphosate resistance in kochia in the region.

One sample collection from Stutsman County, N.D., northeast of Jamestown will survive a normal use rate of 0.75 pounds of glyphosate, acid equivalent, or a Roundup branded product at 22 fluid ounces per acre. “When we get higher than that we’re getting significant mortality, but we can get (some) plants to survive 3 pounds of glyphosate, which is actually a whole gallon of the old formulation of Roundup,” Stachler says.

Another kochia population from Pierce County, N.D., south of Rugby, shows an even higher resistance. The majority of weeds survived a 1.5 pound per acre glyphosate rate, which is “the highest legal single rate we can use in soybeans and twice the normal rate of 0.75 pounds. Most of the plants are surviving, but severely injured. “Worse yet, we have several plants — about 20 percent — that are surviving 6 pounds of glyphosate, or 2 gallons of the old Roundup” Stachler says.

Two years ago, there were reports of problems in Dickey County, N.D., but NDSU couldn’t confirm it in greenhouse testing. The kochia seeds were sent first to South Dakota State University Extension Service weed scientist Mike Moechnig, then to NDSU, and finally to Colorado State University for genetic testing.

“The mechanism for resistance in kochia appears to be multiple copies of an EPSPS (5-enolpyruvyl-shikimate synthase) enzyme, which is where glyphosate inhibits plant growth,” Stachler says. “You have an overproduction of that so you can’t get enough glyphosate in there. There’s so much EPSPS enzyme there’s not enough glyphosate to bind to it to stop plant growth and so they survive.” There are reports of possible kochia resistance in McIntosh, LaMoure and Ramsey counties in North Dakota.

Stachler says North Dakota doesn’t want to end up like Kansas, where every farmer in the western part of the state has to deal with it. “We’re the last place with the least resistance in kochia, with the exception of Montana and farther north. We can make a difference if we want to make a difference, but if we ignore this, Mother Nature is going to spread the problem.”

Now or never

“This coming year, if North Dakota farmers haven’t switched their herbicide programs we need to get growers to actively scout fields and if necessary remove plants when there’s just a few in the field,” he says. “Glyphosate is so effective, we should have no (weed) plants in the field unless we’ve totally messed up due to application or weather. If we see any plants in the field — regardless of the species, but especially common ragweed, waterhemp, kochia, giant ragweed — we need to pull those plants when there’s one or two or a small patch. I can almost guarantee you’ll be completely rid of the resistance problem by doing that.”

Is it practical for a farmer to cover large acreages that way?

Stachler thinks so, but that depends on the size of the operation and how many fields have the problem.

Because there is “low-level resistance” to glyphosate, the herbicide is bound to have some activity even on resistant plants. If farmers have a poor kill, and don’t know why (maybe it’s weather they think) they might use leftover glyphosate to kill weeds that have grown too large for other chemical rescue treatments. But if they don’t physically remove stragglers that have survived they can worsen their resistance problems.

Stachler says farmers and their advisers can’t expect science to come up with a silver bullet to solve the problem, or maybe they can go backward.

The trouble with that is older-class chemicals had been starting to fail before Roundup came on the scene in the 1990s. “If it wasn’t for the introduction of Roundup Ready crops, we likely would not have harvested the amount of crops that we have in the United States in the past 10 years. We were headed to disaster then already, with the old chemicals.”

Stachler worries that if farmers are forced to return to the “old chemistry” — before glyphosate — they’ll have become complacent about how to apply it correctly. “If there’s still resistance in those populations to the old herbicides, and we don’t use them correctly, we’re going to select for resistance even faster.”

He says some farmers today will not touch Liberty Link seed because they were disappointed when they used it in corn several years ago.

“Liberty should be treated as a contact herbicide,” Stachler says. “We have to have high water volume, small droplets, lower travel speeds and good coverage. We have to spray small plants (1 to 2 inches), use the highest rate possible you can use for the conditions. If we don’t do those things, we’re not maximizing activity. Therefore, we’re selecting for the opportunity for weed survival. If you leave the weed plants to produce seed, that’s a problem. We’ve recommended Liberty Link soybeans to a lot of people now. It makes solid, sound science, but if we go out and use Liberty like we did Liberty Link corn in the late 1990s and early 2000s, we’re going to be sadly disappointed.”

Important tool

Glyphosate is too important for farmers to lose, Stachler says. He says a survey showed nearly 90 percent of sugar beet growers in American Crystal Sugar Co.’s growing area reported “excellent” weed control in 2009, compared with less than half that satisfaction with earlier herbicides.

Stachler isn’t aware of any “silver bullet,” waiting in the wings of the crop protection industry. “Do you know how we find herbicides?” he asks. “Simple analogy, it’s a needle in a haystack. We take a chemical, spray it on a plant and see if it has any activity. We spray millions of compounds on an annual basis, to see if there’s anything that will kill weeds.”

The number of companies looking for chemistry solutions has declined from more than 15 to less than half that today.

“There isn’t a single part of the game that’s the same as it was 20 years ago,” Stachler says. It costs three to four times more to bring new chemistry products to the market than it did 20 years ago. Companies want more profit than they did before because they have to spend more. “There are products on the shelf that aren’t coming because either they’re too environmentally damaging and the EPA won’t approve them or they cost too much to make and won’t be profitable for the company.”

Stachler doesn’t think herbicides will be the final answer. “It might be nanotechnology, or some kind of mechanical solution, not yet thought of,” he says. “Maybe we’ll just spray the fields, and we’ll just send a robot out to get rid of those few stragglers, instead of farmers doing the hand labor. It’s going to be something like that. One thing’s for sure — herbicides-only is not sustainable — exclamation point.”

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