What is in this article?:
- Fall residuals for glyphosate-resistant Italian ryegrass
- November applications effective
- Postemergence options for glyphosate-resistant Italian ryegrass in the spring are extremely limited and require at least two applications to even approach complete control.
- Residual herbicides applied in the fall offer the best opportunity for control.
Across the Mississippi Delta, it appears that most farmers are over the hump on harvest if not fast approaching the finish line.
The weather over the last month has allowed for extensive field preparations for 2011 behind corn, soybean, rice, and even cotton in some cases.
The lack of rainfall during August and early September also prevented excessive weed germination following harvest. However, most areas in the Mississippi Delta received at least some rainfall over the past couple of weeks and the summer temperatures are starting to moderate. This means growers in areas with a history of glyphosate-resistant Italian ryegrass should begin to make preparations for another onslaught of this weed.
Last year, glyphosate-resistant Italian ryegrass began emerging during July or August, and this early emergence complicated management programs. However, the late-summer weather conditions in 2010 have been the complete opposite of 2009. We began scouting for emerged glyphosate-resistant Italian ryegrass in mid-August this year, monitoring eight sites from Tunica, Miss., to Yazoo City, Miss.
As of Sept. 21, we had found no emerged glyphosate-resistant Italian ryegrass at any of the sites.
There was a period during the first week of September when the temperatures were conducive for Italian ryegrass germination. In general, if day-time temperatures are consistently below 87 degrees for a week, Italian ryegrass will begin emerging. But, temperature in early September was irrelevant because most areas were so dry. Only when Italian ryegrass gets the right combination of moisture and temperature will seedlings begin emerging.
Historically, the average high temperature at Stoneville falls below 87 degrees on Sept. 14, so Italian ryegrass should begin emerging soon.
In the Mississippi Delta, we have been evaluating management programs for the weed for several years. The primary take-home messages from this work are that postemergence options in the spring are extremely limited and require at least two applications to even approach complete control, and residual herbicides applied in the fall offer the best opportunity for control.
Because so few options exist for controlling glyphosate-resistant Italian ryegrass in the spring, we have begun to focus most of our management strategies on fall applications of residual herbicides. Among the labeled herbicides for which we have multiple years of data, fall applications of Dual Magnum, Treflan, and Command have provided the best residual control of glyphosate-resistant Italian ryegrass.