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The $120,000,000 pest...and that’s just one state

Perhaps you’re taking the Alfred E. Neuman approach to herbicide-resistant weeds: “What, me worry?” If so, Tennessee farmers can give you 120 million reasons why that won’t work.

Back in 2011, Larry Steckel, University of Tennessee Extension weed specialist, calculated that glyphosate-resistant weeds cost Tennessee soybean production $120 million annually. Here’s how.

  • Herbicide costs ran $72,000,000. That’s based on a $45-per-acre cost across 1.6 million soybean acres.

  • Herbicide application tallied $8,000,000. That’s based on $5 costs across the same acre amount.

  • Weed competition losses cost $40,000,000. That’s assuming  30% of impacted acres lose 17% of 35-bushel-per-acre yields at a $14-per-bushel soybean price.

Ouch. That’s a particularly tough blow from a decade ago. Back then, two postemergence shots of glyphosate and application costs for soybeans tallied around $20 and created television commercial-clean fields.

That’s changed. “The total postemergence era is over, and I don’t think it’s ever coming back,” says Steckel.

Glyphosate resistance first surfaced in 2000, when glyphosate-resistant marestail was found in a Delaware soybean field. By 2004, glyphosate-resistant marestail spread across 500,000 acres. In 2005, the first glyphosate-resistant waterhemp biotype in the Midwest surfaced in Missouri. By 2008, one third of 200 Iowa waterhemp populations surveyed resisted glyphosate.

As bad as this was, it was just a warm-up for Palmer amaranth, the biggest and baddest of herbicide-resistant pigweeds.  

“In the South, we are in a mess,” says Ford Baldwin, co-owner of Practical Weed Consultants and retired University of Arkansas Extension weed scientist. “The Roundup Ready technology has been devalued. This is due to a weed with a little bitty seed without a brain that we have trouble controlling.”

So What do you Do?

Mid-South and Southern farms are figuring out how to deal with it through cultural practices like crop rotation, narrow rows, and the use of herbicides that kill weeds in different ways.  

If you’re a Midwestern farmer with no resistance problems, you’re in a great position to prevent problems.

“Resistance management is more proactive than reactive,” says Steckel. “If we look back 10 years in Tennessee, using a combination of a preemergence product followed by a post-product would have delayed resistance, and we would not have had this huge seed bank.”

Following are 13 steps you can take to forestall herbicide-resistant weeds.

1. Know Your Enemy

There are plenty of weeds that resist herbicides. Still, two pigweeds are making life tougher for farmers than many others. In the spirit of the movie Dumb and Dumber, here’s a play-by-play of Worse and Worser when it comes to weeds.

  • Waterhemp’s season-long emergence pattern enables it to exploit even slight canopy openings. It multiplies rapidly in a field; one plant can produce up to 1 million seeds. It also resists multiple herbicide modes of action.

    “Glyphosate does not faze waterhemp in our area,” says Rick DeGroote, a Parkersburg, Iowa, farmer. “The first year, I figured I may have sprayed too early, or that drought may have impacted it. It didn’t take too long to figure out something was wrong.”

  • Palmer amaranth is even nastier. Like waterhemp, it may spawn up to 1 million seeds per plant. It has both male and female plants.

    Female Palmer amaranth plants grow up to 10 feet tall, with a 5-inch girth and seed heads growing over 1 foot.

“Males are small and wimpy,” says Bill Johnson, Purdue University Extension weed specialist. Still, males play a key component by providing the pollen for females to set seed. Left unchecked, your combine can mimic a super seeder by running all this seed across your field.

One other quirk about Palmer amaranth is  pulling and throwing it aside doesn’t work. “This plant will reroot and produce seed,” says Johnson.

It’s important to note many other weeds resist herbicides, too. “We continue to lose the battle on marestail,” says Johnson. “This year, we are losing the battle for different reasons. There was reluctance to use 2,4-D due to delayed soybean planting (because of plantback restrictions).”The result was marestail-infested marestail.

“What I tell people is to assume all marestail is glyphosate-resistant,” he says.

2. Apply Herbicides With Multiple Action Sites

Once you’ve figured out problem weeds, make your plan. Applying herbicides with multiple sites of action helps ensure weeds are killed in different ways.

It’s akin to a baseball pitcher who keeps batters at bay through several pitch types. Killing weeds in different ways keeps them off balance when it comes to developing herbicide resistance.  

“Five years ago, I’d just throw glyphosate in the tank, spray, and be done,” says Kenny Wells, a St. Joseph, Missouri, farmer. “Today, I don’t have that option. I’m tank-mixing more chemistry into one tank, like in the 1980s.”

3. Use Preemergence Herbicides

The easiest way to control weeds is to never let them emerge. “Pre’s really have saved us from having really big problems,” says DeGroote.

Protection varies depending on crop, but preemergence residuals can provide from 30 to 60 days of protection from weeds.

They aren’t foolproof. About an inch of rain within a week after application is required for activation. That often didn’t occur during a droughty 2012.

Rainfall did occur in many areas in 2013, though. “This was a very good year for residual herbicides if you were able to apply them,” says Damon Palmer, U.S. commercial leader for Dow AgroSciences’ Enlist Weed Control System.

4. Don’t Cut Rates

Skimping on chemical label rates doesn’t kill weeds. It just makes them mad.

“Trying to kill it with a (below-label) low rate will just make it come back,” says Scott Church, who farms with his son, Jared, near Catlin, Illinois.

Shaving label rates also enables those weed biotypes resistant or tolerant to a chemical to come back and  multiply. This can cause you problems in future years.

Skimping on rates is also inefficient. You’ll have to spend time and money controlling escapes you could have controlled the first time.

That’s why the Churches always apply label rates to help ensure better weed control.  “If you want better herbicide performance, don’t skimp on rates,” says Jared.  

5. Consider Overlapping Treatments

Mid-South farmers battling Palmer amaranth layer several burndown and preemergence residual treatments followed by timely postemergence treatments, says Steckel. One bright spot is that preemergence herbicides with a mode of action other than glyphosate can curb Palmer amaranth at 3-inch heights. You can then apply postemergence herbicides other than glyphosate – such as Flexstar, a PPO inhibitor.

There’s a catch, however. Herbicide applications must be applied to small Palmer amaranth plants. Flexstar is much more effective on 3-inch-high Palmer amaranth than it is on 6-inch-high plants.

“Spraying Flexstar two days earlier on 3-inch Palmer makes all the difference in the world,” Steckel says. “Weeds choked out the field where Flexstar was sprayed at a 6-inch-weed height.”

6. Brace Yourself for Sticker Shock

Some overlapping soybean preemergence residual and postemergence treatments can tally $50 to $60 per acre, says Johnson. Considering the way Palmer amaranth can take over a field, it can be money well spent.

“Yield losses approaching 78% in soybeans and 91% in corn attributed to Palmer amaranth interference have been reported in scientific literature,” says Aaron Hager, University of Illinois Extension weed scientist.

“Weeds cost you, whether you are paying for chemical or yields lost due to weeds,” says Kismet, Kansas, farmer Brett Reiss.

7. Switch to Narrow Rows

Getting canopy closure is always a good tool to control weeds, says John Merryman, Monsanto technology development representative.  “This year, 30-inch rows are having trouble closing the canopy,” he says.

Not so with rows narrower than 30 inches. “Fifteen-inch rows quickly canopy,” says Reiss.

They yield more, too. University of Illinois trials show 15-inch-row soybeans consistently yield 2 bushels per acre better than soybeans grown in 30-inch rows.

One exception is narrow rows don’t work well in fields prone to white mold. That’s because lack of air movement enhances this fungal disease.  

8. Watch Livestock Feed

Carefully scrutinize livestock feed brought in from out of your area.

“The initial finds of Palmer amaranth in Indiana were around dairies,” says Johnson. “The seed was brought in through dairy rations like cottonseed and cottonseed hulls.”

9. Scrutinize Free Manure

Weed seed spread can also occur by manure. “People have to be cautious about taking free manure from these dairies,” says Johnson. If dairies have fed cattle cottonseed or cottonseed hulls in the past 10 years, Johnson advises first scouting areas where manure is spread or stored for the presence of Palmer amaranth.

10. Control Weeds Adjacent to Fields

Palmer amaranth plants grow in fence rows and drainage ditches. “Birds will eat seeds, and when they land on power lines, they will spread it around,” says Johnson. “Weeds can move out if you don’t provide sanitation on field and drain tile edges.”

11. Harvest Infested Fields Last

Combine your cleaner fields first and the weediest ones last, says Johnson. That way, you won’t be spreading weed seeds from your weediest fields all harvest season. A combine can act as a super seeder, potentially sowing herbicide-resistant weeds on every field round.

12. Scout for Rogue Waterhemp and Palmer Amaranth Plants  

That’s because a few stray plants of these pigweeds can leave up to 1 millions seeds each for next year.

“Mice and birds can take 750,000 of those, but that still leaves 250,000 of them,” says Craig Lamoureux, a Monsanto technology development representative.

What to do? Well, you could take a step from long ago and hand pull them. DeGroote and his employees took some time out last summer to hand-pull rogue glyphosate-resistant waterhemp from his fields.

“It was a 1-acre part in a field,” he says. “I took my employees and we went out and pulled them by hand to prevent them from reseeding.”

13. Prioritize Planting Over Spraying

Planting season is a hectic, hurried time. Still, planting into a weedy field rather than a weed-free one puts the crop behind the eight ball before it even starts.

“Today, I will shut the planter down to spray before I plant a field,” says Wells.

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