What is in this article?:
- Upper Southeast wheat facing real resistant weed problems
- Weeds found resistant to all postemergence herbicides
- Increasing problems with resistance to ryegrass-controlling herbicides is a big threat to this year’s wheat crop in North Carolina.
ANOTHER BIG WHEAT crop is expected in the Upper Southeast this year but herbicide-resistant weed problems loom over the crop.
Weeds found resistant to all postemergence herbicides
The statewide wheat weed resistance study, he stresses, provided some expected and some highly unexpected results. “To find that only two of the sites we tested across the state did not show resistance to Hoelon was not surprising,” he says.
On the other hand, heavy resistance problems in the southeast part of the state to Osprey and Powerflex were surprising. “We didn’t find as widespread a problem with resistance to ALS-inhibitors (Powerflex and Osprey) in wheat in the Piedmont or the northeast part of the state, but resistance to all the available postemergence herbicides did show up statewide,” Everman says.
“The really scary thing is that we found five populations of weeds in wheat that are resistant to every one of the postemergence herbicides we have to control Italian ryegrass. In a situation like that, once ryegrass comes up, you’re stuck with it,” he stresses.
These findings led the North Carolina State University researchers to begin looking for alternative ways to manage herbicide-resistant ryegrass. By chance, Everman was putting in a test for the Northeast Ag Expo and had a choice of no-till or conventional tillage plots to plant his tests.
“For no good reason, I chose both, and that really opened our eyes later to some opportunities to use cultural practices to help manage post-emergence Italian ryegrass in wheat,” he says.
The North Carolina State researchers planted wheat in both no-till and conventional sites in conventional 7.5 inch rows and in narrow (3.75 inches) rows. It was no surprise, he says, that the narrow rows produced the higher wheat yields.
“We had very little ryegrass on these test sites—not even enough to rate the plots, so these became yield studies. They repeated the tests on grower fields with known high populations of ryegrass, but again had little weed pressure.
“We can’t make recommendations on one-year data under such low weed pressure, but our observations are clear. On the narrow row fields we definitely saw less ryegrass,” he stresses.
“Last year we had cool, wet weather, and I think that held ryegrass back. It seems like we are seeing later and later flushes of ryegrass, and this is where the narrow rows may pay off the most,” Everman contends.
The North Carolina State researchers used different combinations of all the pre-plant and spike stage herbicide families used to control ryegrass in wheat in both the no-till and conventional tillage plots.
"Again, these results are sufficient to make sweeping recommendations on—these were primarily demonstration plots, but our observations were clear. Across the different pre-plant and spike stage applications, the no-till wheat was covered up with ryegrass. The tilled plots, with the same herbicide treatments had some ryegrass, but noticeably less ryegrass than the no-till plots," he said.
“Across the board for all the treatments, we got a 30 bushel per-acre yield increase on the tilled versus the no-till plots. This test was on a poorly drained soils, so I believe some of the yield advantage from tillage is to be expected, but I also believe some of the yield advantage came from less competition with ryegrass in the tilled fields,” Everman said.