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Resistant weeds threaten conservation tillage acreage

Since its introduction in the mid-1990s, Monsanto's Roundup Ready technology has allowed U.S. agriculture to adopt an unprecedented level of conservation tillage. Over the last decade, there has been such a steady increase in con-till that it is now accepted as a way of doing business while cutting farmers' costs and bringing efficiency to their operations.

Numerous side benefits include reducing erosion, water conservation and water quality.

“I've got numbers showing the amount of energy expended for cotton production and how much it has decreased in the last 10 years,” says Ken Smith, Arkansas Extension weed specialist. “It's impressive.”

Today, over 70 percent of all the cotton, rice and corn in the United States are devoted to conservation tillage. The wonder of Roundup Ready technology has allowed this. Without exaggeration, Roundup Ready changed the face of U.S. agriculture.

But a dark side has also emerged: glyphosate weed resistance. As Roundup Ready crops were planted on more and more acreage, more weeds were selected out with increasing doses of Roundup (glyphosate). Now, the problem has become so acute in some areas of the South that growers are warning about the loss of con-till acreage. (For more, see

“If herbicide resistance turns us back to tillage, it will be devastating to the con-till gains,” says Smith, interviewed in August. “I visited with a group of major cotton farmers today. They'll tell you, ‘Yeah, we've got to go to more tillage despite not wanting to.’

“One said, ‘If I have to go back to the old levels of cultivation and whatnot, I'll just retire. I'm not going back.’”

Others have told Smith they can't afford to go back. The reason: once a farmer switches to con-till he's able to reduce equipment inventory. Instead of farming 350 acres per tractor, he might use one tractor on 1,000 acres. If he's farming 5,000 con-till acres and has to go back to tilling, he'll need to purchase another 10 tractors at $200,000 per.

Smith and research colleagues are running as fast as they can to find answers on how to tackle the growing resistance problem.

“Farmers are interested in anything they can do to maintain the current level of con-till,” says Smith. “Our goal is to be able to farm cotton in a resistant-weed area with only one in-crop, post-direct herbicide application per year. Everything else would go over the top. But they will have to maintain a hooded sprayer, a post-direct rig — something to allow one application in-crop.”

Earlier this summer, Smith began sounding the resistance alarm with agencies that oversee conservation efforts. Following his presentations, “they were worried very quickly. Thankfully, now it is getting attention from state and federal officials. This is gaining traction.”

Andrew Wargo agrees.

“Weed resistance is hitting us on several fronts,” says the business agent/farm manager for Baxter Land Company in southeast Arkansas' Desha County. “We must get the word out on this. We must come to a meeting of the minds and develop a collective plan among all concerned to not digress with conservation tillage.”

Wargo has been aware of herbicide weed resistance since the 1980s when barnyardgrass couldn't be controlled with propanil. Shortly thereafter, certain cockleburs began showing tolerance to MSMA.

Wargo also accepts his part in the spread of resistant weeds. “Most are now aware that the way to quickly develop a resistance to a drug, a herbicide or insecticide is to continually treat the same problem with the exact same chemistry. It's Mother Nature's way. Resistance develops when you select out those that are tolerant to the treatment.

“When we were provided the blessing of Roundup Ready crops, it was great from an agronomic rotation standpoint. But as far as weeds, we began rotating nothing — it was Roundup 24/7.”

Across the world, some 189 weed species (331 resistant biotypes) have developed herbicide tolerance. In the United States, there are now nine weed species resistant to glyphosate (16 in the world). Waterhemp, Palmer amaranth, Johnsongrass, horseweed and ryegrass are among the most troublesome resistant species.

“We used Roundup before Roundup Ready crops as a target-specific herbicide,” says Wargo. “We used it in recycle sprayers, sometimes with wick-bars over-the-top, and on right-of-ways.

“When Roundup Ready cotton and soybeans came along — at that time, corn wasn't a large player in this area, although more recently it has come in as an alternative crop — they were readily adopted.”

Prior to that, farmers had “quite an arsenal” of preplant, pre-emergence, and post-emergence herbicides. However, as glyphosate became the product of choice — sometimes the only product used by farmers to fight weeds — by the late 1990s the roster of worldwide companies working with developmental chemistry had shrunk.

In the face of chemical company mergers amid spiking glyphosate use, alternative herbicide labels were often allowed to expire and production lines shut down, says Wargo. “Many of the products we used to have are simply gone.”

“Syngenta, Bayer, DuPont, Dow and BASF still have active synthesis groups,” says Smith of the current situation. “A handful of other companies, mostly Japanese, have very active bench chemists. Those mostly synthesize and then sell to another company with a marketing group.”

In the Mid-South, the Roundup Ready system eliminated many erosion problems. Prior to conservation tillage, the combination of, in some cases, a dozen trips across fields and furrow irrigation was causing unacceptable soil losses. The implementation of buffer strips also helped.

Wargo has seen weed resistance develop while serving as an appointed member of the state's County Conservation District Board, a position he's held since the 1980s. For the last several years he's also served on the executive board of the Arkansas Association of Conservation Districts (AACD), a statewide network of conservation districts.

Formed in 1992, the Arkansas Conservation Partnership (ACP) will also play a huge role in solving the state's looming resistance/con-till issues. The ACP is comprised of the Natural Resource Conservation Service (NRCS), the AACD, the Arkansas Association of Conservation District Employees, the Arkansas Resource Development Council, the University of Arkansas Cooperative Extension Service, University of Arkansas-Pine Bluff, the Arkansas Game and Fish Commission, and the Arkansas Forestry Commission.

“It's rather unique to have everyone under the same umbrella,” says Wargo. “In other states, agencies are so embroiled in turf battles it's counterproductive to their effectiveness. In Arkansas, of course, each agency is proud if its role and mission. But through the ACP, we're all working for the common good. Agencies interact and work together almost seamlessly.”

Many times, federal programs require more than one discipline or agency to be fully effective in implementation. The ACP “has been incredible with that.”

Earlier this summer, having been briefed by Smith on the continuing boom in resistance, an alarmed Wargo contacted officials in the state NRCS who received his message warmly. Also, the mid-summer meeting of the National Association of Conservation Districts (NACD) was set to start and Wargo — who was to be a delegate at the Washington, D.C., meeting — figured that would be another place to crank up the volume on weed resistance.

“I called the Natural Resource Committee chairman up there, explained the concerns, and asked to be on the agenda. Basically, at the mid-summer meeting the different committees decide what items will be on the agenda for the annual meeting in February. He agreed.”

Several weeks later, after Wargo finished his presentation, the committee recommended to the NACD board that a task force be appointed to look at weed resistance.

“They want to know what effect resistance is having nationwide. I've since been notified that Steve Robinson, NACD president from Ohio, said it was of concern on a national basis. They're appointing a task force and this will be a full-blown agenda item at the NCAD February meeting in Orlando.

“I was just hoping to bring some attention to it. We don't want to be alarmist, but this resistance has crept in and is taking over.”

In some cases, says Smith, weed resistance has gone undetected “because folks thought, ‘well, the highboy driver missed a spot’ or ‘the tank-mix was weak.’ Too often, that's not so.”

When there are unusually high summer temperatures combined with late summer rains, weeds can come through soybean canopies. In decades past, farmers had only short-term residual herbicides. Normally, the canopy and a lack of moisture would take care of later weeds.

This year, “we've had high temps and lots of rainfall in June and early July,” says Wargo. “That resulted in crops being planted later than normal, the canopy was late closing and weed seed was able to germinate at much higher levels than normal.

“In many cases, we used to think, ‘we'll plant it dirty and clean it up with Roundup.’ That was true behind wheat, having to replant drowned-out crops, whatever.”

In July, “we began hearing horror stories all over the state. ‘Man, there are ankle-high weeds out there that Roundup won't even touch.’ It hit us in the face between rains.”

There are now documented cases in the state where 4X rates of Roundup won't even clean up pigweed problems. And even if it did, asks Smith, “Who can afford a 4X rate?”

Another contributor to resistant weed problems — “and I understand why they took this approach,” says Wargo — are right-of-way crews. Roadsides are mowed much less than they used to be because a light rate of glyphosate can reduce the growth rate of vegetation. This practice has saved taxpayer money, at least in the short run.

However, “now Roundup-resistant ryegrass is alongside every road you drive down. That isn't just because of the clean-up practices — some of it arrived via drainage conduits, which are often alongside roads.”

In many areas, the Mid-South has already reverted back to tillage to control weeds. It's often more effective and economical than utilizing available chemistries.

“We're headed in the wrong direction,” says Wargo. “And we all know it. There are implements running through fields that haven't been used since the early 1990s. Producers have to do it just to survive.

“Who thought chopping crews would be in short supply in 2009? On company land here, there's a farming family growing about 4,500 acres of cotton with seven people. Needless to say, it was only possible to set that up because of Roundup Ready cotton.”

Fortunately, migrant laborers that normally help with the cotton harvest showed up a few weeks early. “They're now out pulling, or chopping, weed escapes. But next year with these resistant weeds taking over so fast? It'll be a whole new ballgame.”

The future isn't “all doom-and-gloom,” says Smith, who points to Bayer's LibertyLink technology as a positive. “There are some regimes where you'd use Roundup one year, Liberty the next, and another product after that. But some of those products still involve tillage because they must be preplant incorporated.”

Also in the mix of worries: residue requirements in some states above the Mason-Dixon Line. In those areas, a certain plant material residue must be maintained on the soil to prevent erosion. The residue level is actually tested and measured by NRCS.

If resistant weeds take over and those fields are tilled, residue will be greatly reduced or destroyed and some fields won't be in compliance with conservation plans. Those fields not in compliance could be ineligible for farm programs.

Over the winter, Smith hopes to be included in roundtable discussions between “county Extension agents, weed scientists, district conservationists, industry folk, the Arkansas Agricultural Council — everyone who has a stake in this — to properly, prudently assess the matter. Hopefully, we can come up with some proactive steps to benefit all concerned. This resistance issue must be tackled before it's too late.”

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