After Wet Spring And Delays, Plenty Of Weeds And Resistance Waiting In 2016

The 2015 corn and soybean crops made a tough start, especially in Corn Belt states but also in portions of the South. Heavy rains and cold weather delayed planting and/or compromised stands. The numbers tell the story. USDA estimates that farmers were unable to plant 2.35 million acres of corn and 2.22 million acres of soybeans. Missouri had the dubious honor of leading in both categories. Missouri farmers ended up not planting 1.05 million acres of soybeans, while more than 500,000 acres of intended corn ground also wasn’t seeded. Wet conditions also played havoc with herbicide programs and further aggravated issues with resistant weeds. Problems varied but included these situations:

  • Heavy rains flushed away residual herbicides, leaving fields open for later germinating weeds.
  • Rains either delayed residual herbicide applications or kept farmers from putting down materials at all.
  • Where people counted on post-emerge or salvage treatments to save the day, weeds often had grown too large for adequate control once farmers could move into their fields again.

All this will likely lead to more weed pressure in 2016, say weed scientists like the University of Missouri’s Kevin Bradley. Often, he points out, those “prevented planting” fields were left fallow and weeds filled up all the empty spaces, then went to seed. (To see his recent post about this click here.) Crop consultants in both the Corn Belt and the South already are thinking ahead to next year’s herbicide programs. In particular, they know they will be dealing with cases where resistance already had taken hold. Many of the tough species – Palmer amaranth, waterhemp, marestail, among them – escaped and went to seed in 2015. For many, this will be a year to remember in terms of runaway weed pressure. “I encountered quite a bit of waterhemp pressure in glyphosate-treated fields and I felt like it was the worst I’d seen in quite a while,” says Michael McNeill, a consultant in Algona, Iowa. “It didn’t matter how much Roundup you put on, there was still a good deal of weed pressure in those fields. So for next year we’ll be talking more about selecting good preemergent herbicides and making sure we apply full rates on a timely basis.”

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Resistant Weeds – Hard Realities For 2016

The hard reality for 2016, says Nebraska consultant Orvin Bontrager, is that farmers in his area won’t be able “to get by with a cheap herbicide program now.” “Growers will have to realize that they’re going to be spending a fair amount of money for this, say $50, $60 or even $70 an acre,” estimates Bontrager of Aurora. “We’re big on spring burndown. As soon as we can get going in March or April most of the fields I look at will be treated.” Nobody in the Corn Belt wants a repeat of the 2015 weed wars, especially in areas where resistant Palmer amaranth has taken up residence. “With the conditions we had at planting in central and eastern Kansas, it was extremely difficult to control Palmer in soybeans once they emerged,” says Dwight Koops, a consultant based in Dodge City, Kansas. “Farmers couldn’t get the pres down and didn’t gain control early enough. We fought Palmer escapes hard with very little success. Our solution is to never see the weed. If we can control Palmer with preemergent products so the weeds never emerge, that’s the strategy to follow.” Midwestern consultants are running up against resistance issues that their Southern counterparts have had to grapple with for a decade or more. Palmer amaranth and marestail are the two that immediately come to mind in the South, but farmers and crop advisors also have been fighting a widening spectrum of other resistant broadleaf weeds and grasses, like Roundup-resistant Italian ryegrass. Farmers in parts of the Delta and Southeast endured early, heavy rains in 2015 that prevented herbicide applications or shortened residual activity where materials were applied. Crop advisors and their farmers are now drawing up new strategies for 2016 that will heavily rely on:

  • Varieties and hybrids with herbicide-tolerant traits other than Roundup Ready. 
  • More fall burndown programs to remove lingering weeds that might make it through the winter. 
  • Overlapping residual applications in some combination before planting, at planting and/or after emergence.

That overlapping residual approach has been widely adopted by many Southern growers. Their aim is to put on the next application before the previous treatment wears out. If weather prevents farmers from making a herbicide application on schedule, enough activity will still be present to hold back escapes. Call it a fudge factor or a bit of weed insurance. But in places with persistent and heavy rain, residual activity can fade earlier than normal, which adds a complication. Resistance has been a factor in the South long enough that all the immediate options have been tried and included in the tool box, either on a regular basis or on an “as needed” remedy if certain situations arise. Many Midwestern growers may think they were in the only part of the country where torrential rainfall delayed planting and/or disrupted weed management schedules. But parts of the South also were affected to varying degrees. “In a normal year we’ll start planting in April, but we had a cool spring this year, which delayed things quite a bit,” says Larry Walker, a Flintville, Tennessee, consultant who works grains and cotton in south-central Tennessee and north Alabama. “When we catch a dry period in March our burndowns go out, but it rained every week in February and March, and we just didn’t dry out.”  He and his farmers scrambled to modify preemerge programs to maintain control, particularly with resistant Palmer amaranth. The weed already presented a challenge, even without application delays.

Palmer Pigweed – No Roundup Option Now

As Walker flatly states, “We can’t control pigweed any more with any rate of Roundup. In 2007 we had an issue with a single patch of weeds. That’s all it takes. Pigweed makes an abundant amount of seeds that spread easily across the landscape and they’ll emerge late, too. That’s the nature of the beast.” In 2016 a residual burndown will go out in the early spring and a preemergent program is in the plan for every acre Walker works. Through parts of the South, farmers and crop advisors seem to relive this wet-spring scenario year after year. But extreme situations also can arise that nullify the very best weed management plans. For example: Hurricane Ana – an abnormally early tropical system – dumped heavy rains over areas in eastern North Carolina around May 9-10. All that water blew apart herbicide programs that had worked fine for decades. “The pres washed away in some cases,” says Billy McLawhorn, a consultant in Cove City, North Carolina. “Let me add that timely, beneficial rainfall is quite common here in the spring. In fact, we’ve had several years in a row with light, frequent rains that usually activated our pres. But a tropical system is an entirely different matter.” “This (2015) was the first year in the past seven or eight when pres generally did not work satisfactorily on the majority of our acreage, McLawhorn says. “In certain areas more Palmer amaranth escaped than I’ve seen since 2008. A lot more post emergent treatments went out this year compared to what we’ve been doing, and people have certainly been more aggressive than they would have preferred to be. And even with that, plenty of weeds had to be hand pulled. Still, though, too much Palmer amaranth was left. You have no problem seeing it as you drive through the countryside.” So, 2016 will be a year to play catch up with weed control in his area, McLawhorn says. For one thing, farmers will make more fall burndown applications than usual. “The other big outcome of our poor weed control this year is that we’ll be more aggressive in adopting the new phenoxy-tolerant traits,” he predicts. For many Southerners, resistance has been further complicated by the fact that multiple species have developed some form of resistance and certain populations carry resistance to more than one chemistry. “Frankly, we’re battling so many resistant weeds that it’s hard to pick just one to focus on,” says Trent LaMastus, a crop consultant based in Cleveland, Mississippi, who works a wide area in the state’s south Delta. “We know we’re going to have to make changes, such as exploring alternating with new traits in the varieties and hybrids we select,” he adds. “We need to alternate technologies like Roundup Ready and look more at LibertyLink, for example.”

His farmers’ weed management practices vary widely, depending on the crop, the field and weather conditions, LaMastus says. “With as much weed pressure as we have coming on, we’ll also see more people going with a fall burndown.” With any luck, the 2016 planting season will start and stay on a more typical track, at least in terms of weather. However, it will begin with more weed seeds than usual, and those seeds are primed and ready to germinate, at least in places. Where those weeds already have shifted to some stage of herbicide resistance, farmers’ practices, approaches and product selection will inevitably change.

Weeds can be controlled but what normally worked a couple of years ago may by useless next spring. This will be a winter to study options and redefine what it takes to start with clean crops and maintain weed control through harvest.

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