Management of Italian Ryegrass in Mississippi

Management of Italian Ryegrass in Mississippi

Dalton Whitt

Mississippi State University

Delta Research and Extension Center

Management

As with any successful weed control program, a multi-faceted approach is the most effective and economical strategy for managing Italian ryegrass.

Mechanical and preventative control

Italian ryegrass seed must be close to the soil surface (<0.5 in) for germination and emergence.  Therefore, tillage prior to emergence could reduce viable seed density in the germination zone of the soil profile.  Italian ryegrass seed last in soil for 12 to 18 months, so populations can be reduced with successful (95%) control for 1 to 2 years.  Chaff collection systems may aid in reducing seed present after crop harvest.

Chemical control

Mississippi producers historically relied on postemergence spring burndown herbicide treatments to control Italian ryegrass.  These typically included a nonselective product such as glyphosate or paraquat plus a residual herbicide to prevent new emergence through time of crop planting. Other programs utilized mixtures of glyphosate plus clethodim plus broadleaf herbicides such as 2,4-D or dicamba.

One issue with postemergence spring burndown herbicide treatments is that the targeted winter weeds often exceed the labeled size for acceptable control by the time of the application.  Another issue limiting the success of postemergence spring burndown treatments is weather.  Springtime weather conditions can vary drastically and change quickly in Mississippi.  This often leads to herbicide applications during suboptimal conditions when target plants are stressed and not actively absorbing herbicide, thereby reducing control and selecting for herbicide resistance. These factors led many producers to utilize herbicide treatments in the fall.

Success of fall-applied burndown herbicide treatments relies heavily on precise application timing.  If an application is too early, residual control may dissipate before the conclusion of the window for fall and winter weed emergence, leading to more escaped weeds during spring. Conversely, delaying fall-applied burndown herbicide treatments may hinder successful herbicide application to due deterioration of weather conditions.  Therefore, a rule of thumb for fall-applied burndown treatments is to plan applications for the last period of dry weather after October 15.

The following residual products are effective for controlling Italian ryegrass as fall-applied burndown herbicide treatments (Note: The following active ingredients are marketed under a variety of tradenames.  Tradenames listed are for reference.):

• Clomazone (Command)
• S-metolachlor (Dual Magnum, etc.)
• S-metolachlor + metribuzin (Boundary, etc.)
• Pyroxasulfone (Zidua SC, etc.)
• Flumioxazin (Valor, etc.) may be mixed with any of the listed herbicide products to complement Italian ryegrass control and target broadleaf weeds.
• A nonselective herbicide should be included for control of emerged weeds.
• For herbicide rates and additional information please see specific herbicide label instructions. Herbicide labels may be found at the following websites: greenbook.net and www.telus.com/agcg/en-us

When applications are timed correctly, the above fall-applied burndown herbicide treatments have proven effective for Italian ryegrass control; however, escapes may still occur and require either spring tillage or a postemergence spring burndown herbicide application.

Traditionally, postemergence control of escaped Italian ryegrass in Mississippi has involved clethodim or paraquat.  However, level of control with these herbicides is dictated by the target population.  Many Italian ryegrass populations in Mississippi have documented resistance to clethodim and recently, several populations in Bolivar, Sunflower, and Washington counties are suspected to be paraquat resistant.  If a population is resistant to both clethodim and paraquat, no other effective postemergence herbicide options are available, meaning successful fall-applied herbicide treatments are even more critical.

Conclusion

Italian ryegrass remains the most troublesome winter annual weed plaguing Mississippi row crop producers; however, by diligently implementing integrated pest management principles, infestations of this weed can be nearly eliminated.