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What might be the fallout from PPO-resistant pigweeds?

What might be the fallout from PPO-resistant pigweeds?
The issues surrounding PPO-chemistry resistant pigweeds. Concerns for Mid-South farming landscape.

Now that PPO-resistant pigweeds have been confirmed in the Mid-South how might things shake out in the future?

“The PPO chemistry has been the backbone of weed control for cotton,” says Jason Norsworthy, University of Arkansas weed scientist. “We use Reflex pre-plant and that’s been a mainstay for pigweed management. Take that out and it’s going to make weed control in cotton more challenging, especially in Roundup Ready cotton.

“You’ll still have some options pre-plant with Direx and Cotoran and Caparol and things like that. But the PPO resistance, again, is going to  impact Roundup Ready cotton.”

Arkansas cotton acreage has largely shifted to Glytol LibertyLink, says Norsworthy. “We’re also seeing a decent amount of Roundup Ready Flex cotton planted this year.

“In a PPO-resistant pigweed situation, between cotton and soybeans I think cotton is in the better position. You’ve got Cotoran and Direx along with products like Dual and Warrant.”

In Mississippi – where PPO-resistant pigweeds are yet to be confirmed --  Jason Bond is extremely suspicious the weed’s evolution has occurred. “We’ve seen plenty of failures recently,” says the Mississippi State University Extension weed specialist. “This is a terrible year to see a new resistance case to pop up. With some of these fields, you have to believe it can’t be anything but resistance.

“In the case of pigweed, there are fields where everything else – the targets of the application – is dead. We’ve had unexplained failures where the application was made properly, the timing was appropriate. Everything points to a situation where the spraying should have worked.”

Bond and colleagues are “chasing down these cases, just like they are in Arkansas and Tennessee. After the PPO news broke, I believe it was  Ford Baldwin (veteran weed scientist and Delta Farm Press columnist) who tweeted ‘Is anyone really surprised?’ He’s right: I don’t think anyone who’s been following this even moderately is shocked. But I hate that it has finally arrived.”

One of the potential problems in 2016, says Bond, “is if PPO resistance is more widespread than we now suspect. There may be some guys in a Roundup Ready system that get blindsided.”

Norsworthy agrees. “Jason is absolutely right to be fearful about that. Anytime you find one of these resistant pigweeds, there are bound to be more. History has shown us that first one is just an indication the cat’s out of the bag. I’m not saying 40 or 50 percent of the acres will be infested with PPO-resistant pigweeds next year. But put your money on the fact they’ll be on more than the one or two sites where we’ve found them so far.

“Remember, in 2006/2007 there were just a few glyphosate-resistant pigweeds confirmed. By 2009, they’d become widespread across Arkansas. Those dynamics haven’t changed.”


So, will more Mid-South soybean producers consider planting more LibertyLink varieties? The answer is a mixed bag.

“I’ve heard from growers this past week and they’re indicating a move to more LibertyLink soybean acres,” says Norsworthy. “With Roundup Ready, if you have pigweeds that come through your pre-emergence program the PPO herbicides are basically the only control option. Well, if this PPO resistance goes viral like the glyphosate resistance did it’s going to be extremely challenging to manage.

“If we lose the PPO chemistry, there’s only one over-the-top herbicide for soybeans: Liberty. That’s it.”

Will this mean more LibertyLink in Mississippi?

“We’ve got some hot spots where LibertyLink has been planted in the state,” says Bond. “But it hasn’t taken off to the extent it has in Arkansas. We’ve put a lot of glufosinate on cotton, whether LibertyLink, GlyTol LibertyLink or Phytogen. That’s particularly true in the north Delta.

“On the soybean side, LibertyLink hasn’t seemed to take off here. But for some producers, that will be the only option until the Xtend and/or Enlist soybeans hit the market. Regardless, I don’t see our soybean acreage going 90 percent in either of those new technologies in the first year. Producers are going to want to know how those will work out on big acres and they get comfortable.”

And that comfort should come. According to Jeremy Ross, University of Arkansas soybean specialist, there are several high-yielding LibertyLink soybean varieties that have performed well in trials throughout the state.

How widespread?

Another factor with the confirmation is just how spooked growers currently are over the new resistance development.

The real problem “is if the resistance is in a wider region than we now think,” says Scooter Hodges, an Arkansas-based sales representative with Jimmy Sanders. “If that’s the case, it could mean some growers get caught with their pants down. That’s another reason to consider rotating out to corn or grain sorghum, even if the price isn’t fantastic.

“The thing with all these technologies is you have to start with a great genetic base. If the genetics aren’t there, the technology isn’t worth it. You’ve got to have the balance right.”

That balance is essential for a successful farming operation says William Johnson. “With a lot of pre- programs, you still have to use PPOs to control pigweeds with Liberty,” says the Pioneer agronomist. “And you have to spray Liberty very quickly. The pigweeds can’t be allowed to get any size to them.

“Also, Dual and atrazine are still pretty doggone good on Palmer pigweeds.

“No matter what, soybean varieties have got to be conducive to a Mid-South environment. Who cares if you’ve got all these wonderful traits if the harvest is a disappointment?

“With these PPO-resistant pigweeds, you’re going to see more rotation from beans to corn and milo. The thing with corn and grain sorghum is they come up early and shade the ground before the pigweeds wake up. Pigweeds are still yawning until the soil temperature hits 65 or 70 degrees. Well, by that time, grain sorghum and corn are already growing. And $5 grain sorghum should make that rotation easier for growers to go with.

“Think about it: every time we get a new technology in soybeans, it’s gone in just a few years. You can’t expect different results when some producers are planting soybeans for five straight years and applying the same herbicides.”

With the PPO-resistance popping up, “producers are going to have to run a tighter ship than they ever have,” predicts Hodges. “Things like the timing of herbicide applications are so important. The weed scientists have been talking about that forever.

“You know, some growers don’t like putting a pre-plant (herbicide) application out. They don’t like the expense. But that thinking has to be reversed in this new environment.”


Even with the new resistance, there is a bit of hope on the pre-emergence side, Norsworthy says. “In the Midwest, where there’s PPO-resistant waterhemp, even though it’s resistant post-emergence there is some efficacy of PPOs pre-emergence. That efficacy, though, is less than what we’d normally get out of products like Flexstar or Reflex. So, I don’t think the PPOs will be total zeros pre-emergence on our pigweeds. But that’s total speculation at this point.”

Back in Mississippi, Bond and Bobby Golden, Mississippi Extension rice and soil fertility agronomist, have been in the withering August heat checking rice fields. “Starting the middle of (the week of July 20), we’ve gotten a lot of calls on glyphosate drift on rice. We’ve been visiting some of those fields today and there’s quite a few acres of damage.

“It’s disturbing because it’s so late in the season and the rice is in the process of heading and flowering. It’s a terrible time to be hit with drift because most of the investment is in the crop. The outcome is unknown until the combines roll.”

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