Controlling Ryegrass Late

DR. LARRY STECKEL

JACKSON, TENN.
   Ryegrass questions have become much more prevalent this week. I have had no good answers for the calls on how to control ryegrass that escaped the glyphosate burndown in emerged corn. Herbicides like Accent or Steadfast will not control ryegrass. Liberty tankmixed with atrazine on LL corn would burn the ryegrass back some and is the only even fair option that is available.
   Therefore it is critical to control ryegrass before the corn emerges.  Fortunately, we do not have the widespread glyphosate-resistant ryegrass that is present in the Mississippi Delta. The ryegrass they struggle with is 100 percent resistant to glyphosate. They often apply 16 ozs of Select Max as their best treatment and are still not getting complete control.
   The supplemental label for Select Max (clethodim) use as a burndown in corn has been the “go to” option for many in Tennessee. That label states that Select Max can be applied at a rate up to 6 oz/A 6 days before corn planting. For the most part we have had good control of ryegrass with Select Max used in that fashion. Moreover, many growers often tankmix the Select Max with 32 oz/A of glyphosate. The reason this has been fairly effective for us is that our ryegrass population ranges from moderately glyphosate tolerant to highly glyphosate resistant and as a result we often get some help controlling ryegrass with the glyphosate if it is only somewhat tolerant.
   Another option that has worked for ryegrass control in corn is a sequential application of Gramoxone spaced about 7 days apart. This is, of course, more expensive and delays corn planting more than the Select Max option.
   In cotton or soybean, the best option is again with clethodim. However, it can be applied POST in both those crops so a burndown of Gramoxone PRE plant or PRE followed by a POST application of clethodim works well. If the ryegrass is well established and poses a planting problem, then a burndown utilizing a higher rate of clethodim (Select Max 10 to 16 ozs) plus glyphosate (Roundup PowerMax 32 ozs) has been consistent controlling ryegrass. Both cotton and soybeans can be planted back immediately after a clethodim application. ∆
   DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee