One of the main objectives in our Italian ryegrass control research in 2010-11 was integrating the fall residual herbicide programs with spring burndown applications. The take-home message was glyphosate-resistant Italian ryegrass management must include both fall and spring control tactics.

One benefit of fall management, whether it is a residual herbicide application or tillage, is keeping the ryegrass population low enough for good spray coverage during spring burndown. We have observed fair glyphosate-resistant Italian ryegrass control with clethodim (Select Max or equivalent 2 pound product) applied in January followed by paraquat in early March.

However, where ryegrass densities were high, spray coverage from postemergence treatments was poor, so some plants survived while smaller plants never got treated because the herbicide was intercepted by the dense ryegrass canopy. When the same clethodim followed by paraquat spring program was preceded by a double-disking treatment in November, glyphosate-resistant Italian ryegrass control was 94 percent.

During most years in the Delta, November is not a good time to disk a field, so finishing field preparation earlier in the fall, and then following that with a combination of a residual herbicide plus paraquat in late October to early November will ensure having manageable populations of glyphosate-resistant Italian ryegrass in the spring.

In our research last year, we observed 98 percent glyphosate-resistant Italian ryegrass control in late March when a November application of Dual Magnum (1.33 pints per acre) was followed by clethodim (Select Max at 12 ounces per acre) in January OR paraquat (Gramoxone Inteon at 4 pints per acre) in February. When Dual Magnum was utilized in the fall, only one cleanup application was needed in the spring. But, when the plots were only disked in the fall, then both clethodim and paraquat were required in the spring.

Glyphosate-resistant Italian ryegrass infests a large acreage in the Mississippi Delta and has spread to Arkansas and Louisiana. Its broad emergence window and rapid growth can make it difficult and expensive to manage. The good news is that glyphosate-resistant Italian ryegrass does not possess the same devastating potential as Palmer amaranth.

Although it can negatively affect crop emergence and seedling growth (especially corn), it is a winter weed and control can be addressed before planting without the complicating factor of having a crop present. Also, we have seen cases where aggressive control tactics employed over two to three years have reduced populations to much more manageable levels.

For a comprehensive glyphosate-resistant 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/crops/weeds/herb_shortlist_lolmu_08-20-10.pdf.