Annual ryegrass (Lolium multiflorum) is the most damaging weed in soft red winter wheat in the Northern Texas Blacklands. Annual losses from this pest in the region run in the millions of dollars.
When the sulfonylurea (SU) herbicides (Amber, Glean) were developed in the mid 1980s, they provided excellent control of this weed. However, over time, efficacy of the SUs has decreased, causing the weed to reemerge as a difficult problem for area wheat producers. It has been shown that this ryegrass is resistant to SU and imidazolinone (IMI) herbicides and both have ALS mode of action.
Hoelon replaced Amber and Glean in the late 1980s, but its effectiveness has been declining over the past few years. Axial was introduced in 2008 and has been the most efficacious herbicide for the control of annual ryegrass in recent years. Although Axial XL is still providing good ryegrass control in about 90 percent of regional wheat fields, we are beginning to see some reduced control with Axial XL in a few fields across the region.
Annual ryegrass populations in cropland can be greatly reduced by using cultural and mechanical means in combination with chemical control techniques. Some cultural control suggestions include the following:
- Use certified seed or clean your bin run seed prior to planting. This is an inexpensive way to keep your ryegrass infestations confined to specific fields and minimize spread to non infested fields.
- Thoroughly clean harvesting equipment before moving from infested fields to minimize the spread of ryegrass seed.
- In conventional tillage systems, use mechanical tillage to remove the first flushes of ryegrass prior to fall planting.
- In minimum tillage systems, use glyphosate to destroy existing ryegrass plants prior to planting.
- Rotate wheat with other crops whenever possible. Rotation with corn, soybeans, grain sorghum, and cotton will greatly reduce ryegrass seed carryover from year to year.
Although cultural control techniques can help reduce populations of herbicide resistant ryegrass, an effective chemical control program is also needed. We have been working with new strategies to control ALS resistant ryegrass for more than 10 years. Over that period of time, we have identified a herbicide program that shows promise in controlling this difficult to control weed.
Our most consistent results have come by combining Axiom, a product developed by Bayer, with Axial XL in a two step program. On ALS resistant ryegrass, the two step program (Axiom fb Axial XL) provided significantly better ryegrass control than either product applied alone in both studies. This approach uses multiple chemistries to help decrease herbicide resistance to Axial.
We have not observed crop injury with Axiom on Pioneer 25R47 soft red winter wheat (SRWW) but we do not have sufficient information to recommend this product on many of the SRWW varieties being grown in this region. Research conducted by Bill Williams of LSU suggests that two other commonly grown varieties in the region, Coker 9553 and Magnolia, will also show good tolerance to this program. Terral LA 841, USG 3295, and USG 3555 are likely to be more sensitive to injury.
More research needs to be done to determine crop safety on other popular varieties in the region before we can recommend widespread use of this product on other varieties. Until we have better information on varietal tolerance, we suggest using no more than 6 ounces of Axiom per acre in the two-step program.
Two step program
Step 1: The Axiom should be applied when the wheat is fully emerged and the ryegrass is in the spike to two-leaf stage. Do not use a surfactant with Axiom as it may cause injury to the wheat.
Step 2: Axial XL needs to be applied when the ryegrass plants are in the two-tiller stage.
At present, no labeled herbicides are available to replace Axial XL if widespread ryegrass resistance begins to expand across the region. We believe this resistance management approach will keep Axial XL around as an effective management tool for controlling annual ryegrass in this region for years to come.
The loss of this product would be a disaster to the wheat industry in North Texas. We would likely begin to see fields that would have to be taken out of wheat production for a number of years. Since wheat is our most consistently profitable crop in this region, the negative implications to the agricultural economy would be significant.