Glyphosate-resistant (GR) Italian ryegrass has been documented in Mississippi and growers have been forced to adopt practices to manage it. GR Italian ryegrass has been shown to significantly reduce corn yield and is troublesome in cotton and soybean if not controlled. LSU AgCenter weed scientists currently have samples from multiple locations in Louisiana where glyphosate did not control the Italian ryegrass populations this past spring. Preliminary data indicates that GR Italian ryegrass is present in Louisiana. As a consequence, Louisiana crop producers need to begin mitigation/management programs.
Drs. Jason Bond and Tom Eubank, weed scientists with Mississippi State University, have published excellent programs to control GR Italian ryegrass in corn, cotton, soybean, and rice. The programs can be found at http://msucares.com/pubs/infosheets_research/i1355.pdf. Their research has shown that fall applications of Dual Magnum at 1.33-1.67 pints/acre (corn, cotton, soybean), trifluralin at 3 pt/A (cotton, soybean), Boundary at 2 pints/acre (soybean), or Command at 2 pints/acre (rice) provide excellent control of GR Italian ryegrass. Boundary has received a 24c label for fall application in Louisiana.
All afore mentioned fall-applied herbicides should be tank-mixed with paraquat at 0.5-0.75 lbs. a.i./acre to kill any emerged Italian ryegrass. Their research also showed that double-disking in the fall is another option. In mid-January to mid-February, either 12-16 oz./acre of Select Max or the equivalent rate of a 2 lb/gallon clethodim is needed if Italian ryegrass begins to emerge, but a 30 day preplant interval is required if corn or rice will be planted. In the spring, if glyphosate applied as a burndown is not effective for control of Italian ryegrass, their research indicates that two applications of paraquat at 0.75-1.0 lb a.i./acre spaced 14 days apart will be required for control. Adding either atrazine (corn) at 1 quart/acre, metribuzin (soybean) at 4 oz./acre, or diuron (cotton) at 1.5 pints/acre with the first paraquat application will increase efficacy of paraquat against GR Italian ryegrass.
Steps should be taken to mitigate and/or manage GR Italian ryegrass. If you have questions, please call your local LSU AgCenter county agent or Dr. Daniel Stephenson (318-308-7225) or Dr. Donnie Miller (318-614-4044).