Resistant Italian ryegrass poses threat to Southern Winter Wheat
Jun. 23, 2010
Resistant Italian ryegrass populations have increased across the southern winter wheat growing regions and are continuing to threaten wheat production in the region. In response, Syngenta Crop Protection is piloting an in-season resistance test called RISQ (Resistance In-Season Quick test) in conjunction with Dr. Nilda Burgos and the University of Arkansas.
Once isolated to the west-central area of the Delta region, glyphosate -resistant Italian ryegrass populations now span from Arkansas to North Carolina. In addition, studies have confirmed that populations of the yield-robbing grass weed have developed resistance to ACCase-inhibitor and ALS-inhibitor herbicides.
"The in-season resistance test can determine whether or not a particular weed biotype is resistant to a herbicide within 10 days,” said Don Porter, herbicide technical brand manager for Syngenta. “We are currently working with Dr. Burgos to conduct additional experiments before making this resistance test available on a larger scale and over an expanded geography.”
More extensive resistance testing is available through the Syngenta Vero Beach Research Center where research scientists screen suspected resistant weed seeds collected by Syngenta personnel for resistance to various chemicals and different modes of action.
Growers, retailers and consultants can take a proactive role in monitoring for resistance through early scouting. “Italian ryegrass is an extremely competitive weed and has become a huge concern for our growers,” explained Dr. Dick Oliver, weed scientist for the Division of Agriculture, University of Arkansas. “In studies we’ve conducted, Italian ryegrass can reduce wheat yields by up to 70 percent, so identifying and controlling the weeds before they can cause that yield damage is very important.”
The similar growth habit of cereal crops and Italian ryegrass contributes to its competitive nature. When Italian ryegrass emerges with wheat, it chokes out the crop and lowers yield. Italian ryegrass is a prolific seed producer, and those seeds germinate rapidly at rates between 71 and 80 percent in a two-week span. If Italian ryegrass is not controlled early, seeds can be further dispersed across the field during harvest as a result of combining.
As growers prepare for the 2010-11 winter wheat planting season, a burndown application of Gramoxone Inteon® herbicide this fall can provide residual weed control and help reduce Italian ryegrass populations. Scouting should begin soon after wheat is planted, and a follow-up post-emergence application should be made if Italian ryegrass is present.
Unpredictable weather can lead to unexpected weed flushes. August 2009 brought unseasonably cool temperatures, which in turn brought large populations of Italian ryegrass that growers across the Delta continue to battle in multiple crops. In situations like this, postemergence herbicides become necessary.
"In wheat, we recommend using a soil-applied herbicide, followed by a postemergence herbicide like Axial® XL, or sometimes even a split postemergence application,” Oliver said.
Axial XL can be applied to Italian ryegrass from the 1- to 5-leaf stage before the third tiller has emerged, and it can be applied to the crop from the 2-leaf stage up to the pre-boot stage. This means that if the weather is bad or other factors delay a herbicide application, the window for Axial XL will still be open.
"While Axial XL has proven to be extremely successful in controlling Italian ryegrass in wheat, it’s important to implement sound resistance management practices to ensure we maintain the effectiveness of this herbicide,” Porter emphasized. “Utilizing a diverse crop rotation to extend the range of available herbicides and rotating Axial XL with a Group 2 herbicide are effective resistance management practices for controlling Italian ryegrass.”
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