pigweed in soybeans

A brief look back at 2016: PPO resistance, dicamba drift and soybean weed control

Weed scientists warned producers not to play footsies with PPO-resistant pigweeds and now say the earlier assessments were spot on.

Throughout winter meetings in 2015/2016, weed scientists warned producers not to play footsies with PPO-resistant pigweeds. The resistance, they fretted, would expand rapidly — or, more worryingly, perhaps it already had.

Now, on the tail-end of the 2016 growing season, Bob Scott, University of Arkansas Extension weed scientist, says the earlier assessments were spot on. “I think it’s widespread, like we thought it would be, especially north of I-40. A lot of the populations north of I-40 have at least a portion in the field that carry that resistance.”

Cautionary Tale

In early June, producer Perry Galloway walked into a 70 acre soybean field just north of Gregory, Ark. It looked deceptively healthy and, at one point, had been marked to be a yield contest field.

But a few rows in, the problems were apparent: soybean plants were ragged and leaves splotchy. A closer look revealed a plethora of small pigweeds.

As it turned out, the first field with established PPO-resistant pigweeds in Arkansas is only about 1.5 miles up the road from that 70 acre field. “I’ve been farming this field for six or seven years,” Galloway says. “So, sometime recently, the PPO resistance jumped the road — or has just been building over the years.”

Galloway, who would later replant the field, offers his situation as a cautionary tale for other producers.

“I tried to squeeze one more year out of Roundup Ready, and figured if we could establish a canopy early we’d outrun the pigweeds. I was wrong — we’re out of bullets, except for LibertyLink. Now, we’re hoping for a 70 bushel yield, and that’s a heavy price to pay for this education.”

Residual Programs

Scott says many quickly paid attention to advice he and colleagues gave — and that’s a change from years past.

“We have a lot of LibertyLink soybeans, and lots of guys have gotten serious about their residual programs. They apply effective products with overlapping pre- treatments. A lot more growers are now paying attention to this.

“Last year, the way PPO resistance kicked off was eerily familiar to the way glyphosate resistance blew up. We had that same feeling, déjà vu, with PPO resistance. The difference was that growers have heeded the warnings much more quickly. They’re growing Liberty soybeans, and are putting corn in the rotation. Where they did stay with Roundup Ready soybeans, they had aggressive pre-emerge programs.”

While they have survived PPO resistance, “a lot of growers have spent lots of money on some fields,” says Scott. “Those fields are hard to keep clean, and it’ll definitely be a challenge again in 2017.”

Dicamba Drift

Another story for the 2016 soybean crop was drift damage related to illegal over-the-top applications of dicamba on dicamba-tolerant varieties.

With harvest nearly complete, what might that have done to yields?

“Not surprisingly, yields have been all over the board,” says Scott. “Some fields have had heavy damage on one side and not the other. Yields were down on the side that was hit. On the other hand, there were fields that had ‘cupping’ damage all over, and have yielded within 10 percent of what the grower was expecting.

“If you look at the data — especially Weed Scientist Tom Barber’s studies on application timing — it’s instructive. When did the drift occur? What stage were soybeans in? How much dicamba got on them?

“If beans were vegetative, it may have led to a lot of cupping, but at the end of the day, they yielded okay. If beans were reproductive at R4/R5/R6, we’re seeing more of an impact on yield.”

It’s not a single, common story. “I might talk to one guy who says the drift didn’t hurt his yields,” says Scott. “His neighbor, meanwhile, only cut 30 bushels. If you look at the data, it makes sense.”

Harvest Aids

Scott took a lot of calls on harvest aids. “They were looking for recommendations on burndown. Some had some green leaves and the like. It seems there’s a trend toward more ‘automatic’ harvest aid applications. They want to get the crop out of the field a bit faster.

“I’ve had reports that some fields were dried down a little too much. So, we’re reluctant to make a blanket recommendation for harvest aids. You really need to make sure the timing is right before making the application.”

There are also label issues. “There are pre-harvest intervals, and depending on the product you choose, they need to go out a certain number of days prior to harvest. A lot of those are listed in the MP44 recommendations.”

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish