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- Glyphosate resistant pigweed currently may be attracting more attention, but to an increasing number of wheat growers, herbicide resistant ryegrass poses an equally disturbing dilemma.
“Farmers should consider more than just herbicide for managing resistant ryegrass,” Swart said. “We always recommend crop rotation. If we can get the field out of wheat for two years, we go a long way in reducing resistant ryegrass populations.”
He said a reduced-tillage approach, using a burndown herbicide ahead of planting in a stale seedbed, also holds promise for improved control. “We may be able to knock out 80 percent to 90 percent of the resistant ryegrass with glyphosate,” he said.
Driver said it’s important for farmers “to start clean. Use a burndown herbicide in the fall to clean the fields before planting.”
Driver and Bayer representative Hap Hazzard, say the two-step program has proven an effective way to use both Axiom and Axial XL effectively. “The two-step program has worked well all the way down into the Austin area,” Hazzard said.
“We understand this is a good way to control resistant ryegrass,” Driver added.
Swart said research plots have shown that more than resistance may be the reason farmers are seeing ryegrass escapes. A graduate research project shows that resistant ryegrass may have two flushes, the second occurring after initial herbicide applications have run out.
Swart said the two-step approach takes out the first flush with Axiom. “It also predisposes the resistant ryegrass to Axial XL,” he said.
Soil type also plays into the resistance issue. Swart and others say resistant ryegrass rarely shows up on blackland soils. “We see it on poorer soils, gray land,” he said. The thinking is that farmers have few rotation choices with the lighter soils and don’t rotate as often. The wheat monoculture means reliance on the same or similar herbicides year after year. Resistant ryegrass builds up on continuous wheat.
“Farmers tend to rotate more on better cropland,” Swart said. Heavier soils provide more options, including corn and grain sorghum.
Swart walked the field day participants through herbicide trials, including wheat plots a graduate student seeded with resistant ryegrass harvested from the nearby field that failed last year. “We know this ryegrass is resistant,” Swart said.
He said the hope is that harvested plots will demonstrate the potential yield loss caused by various levels of ryegrass infestations. Plots included ryegrass seeding rates from 15 to 120 pounds per acre.