Fall Herbicide Applications For Glyphosate-resistant Italian Ryegrass

With dry weather across much of the Delta over the past few weeks, many growers are making fall residual herbicide applications for glyphosate-resistant (GR) Italian ryegrass.  As with GR Palmer amaranth, the best time to control GR Italian ryegrass is before it emerges.  At the Delta Research and Extension Center, we have evaluated fall applications of residual herbicides for control of GR Italian ryegrass since 2005.

This research has established that residual herbicides applied in the fall offer the best opportunity for controlling GR Italian ryegrass.  Forty-six different residual herbicides have been screened in field studies for efficacy against GR Italian ryegrass.  Boundary, Command, Dual Magnum, Harness, Outlook, Parallel PCS, Treflan, and Zidua effectively control GR Italian ryegrass for 120 to 150 days if the applications receive rainfall adequate for incorporation.  Unfortunately, only Boundary, Command, Dual Magnum, Parallel PCS, Treflan, and Zidua are labeled for fall applications.

Recently, questions have been asked about the use of Warrant in fall applications for Italian ryegrass control.  Warrant is in the same herbicide family (chloracetamide; Group 15) as Dual Magnum and Parallel PCS, and these herbicides have similar in-season use patterns.  Warrant now has a supplemental label for at-planting applications in soybean and cotton.  However, it is not labeled for application to fallow fields in the fall or winter.  Dual Magnum and Parallel PCS have special local needs labels that allow application from September 1 to November 20 for control of GR Italian ryegrass.  The table below shows GR Italian ryegrass control with different fall residual herbicides in 2011-12.

All fall applications of residual herbicides should include paraquat to control emerged GR Italian ryegrass at the time of application.  For a comprehensive GR Italian ryegrass control program, see Mississippi State University’s “Herbicide Programs for Managing Glyphosate-Resistant Italian Ryegrass”, which can be accessed at http://msucares.com/pubs/infosheets_research/i1355.pdf.