Italian ryegrass (Lolium perenne ssp. multiflorum) is a serious weed in wheat production and continues to spread across much of Mississippi. The increasing prevalence of Italian ryegrass in grower fields is compounded by the lack of control from many commonly used herbicides, such as ALS inhibitors (Group 2) and glyphosate (Group 9). There were frequent instances last spring where glyphosate-resistant Italian ryegrass was not effectively controlled in corn and soybean fields that likely produced an abundance of seed. Much of this seed will consequently emerge and compete with fall-seeded wheat. To further complicate this issue, much of the Italian ryegrass in Mississippi has also been documented as ALS-resistant. Products containing ALS-inhibiting herbicides historically used to control Italian ryegrass in wheat include Osprey, PowerFlex and Finesse Cereal & Fallow. This severely limits the number of effective herbicides to control Italian ryegrass in wheat.
Our research has shown that a program including Axiom (Group 5 and 15) applied just after wheat emergence followed by Axial XL (Group 1) is effective in controlling Italian ryegrass in wheat. Unfortunately, early indications are that there is a limited supply of Axiom available for this growing season. Alternative herbicides for Axiom would include a combination of Prowl H2O (Group 3) and metribuzin (Group 5). While both Prowl H2O and metribuzin alone have good activity on Italian ryegrass the combination of these herbicides provides a much higher level of control.
Prowl H2O may be applied after wheat has emerged and reaches the one-leaf stage but prior to flag leaf emergence. The rate range for Prowl H2O is 1.5 to 2 pints/A on coarse soils, 1.5 to 3 pints/A on medium soils and 2 to 3 pints/A on fine soils.
Metribuzin has a much greater rate range based on crop growth stage, soil texture, and organic matter content. Follow the table below for specific rates to be used.
Caution should be used when applying metribuzin to wheat as there are varietal differences in crop tolerance. For additional information on wheat tolerance of metribuzin refer to the herbicide label or Evaluation of Wheat Varieties for Metribuzin Tolerance.
While a combination of Prowl H2O and metribuzin can be effective in preventing Italian ryegrass emergence, a sequential application of Axial XL applied to one to two tiller Italian ryegrass escapes may be necessary. There have been reports in both Arkansas and Tennessee of Axial XL failures on Italian ryegrass. Fall-applied residual herbicides are important because they can reduce early season weed competition and utilizing herbicides with multiple modes of action is critical to maintaining the effectiveness of Axial XL and other herbicides.