What is in this article?:
- Glyphosate-resistant Italian ryegrass.
- Early burndown applications.
- Control prior to planting corn.
- Italian ryegrass field day.
Early burndown application
Making an early burndown application in January or early-February for Italian ryegrass allows time to determine how well the first application worked and flexibility in deciding how to control escapes.
An early burndown targeting Italian ryegrass is more critical in fields to be planted to corn than those that will be planted to other crops. The window for burndown herbicide application is shortened in corn because of the early planting dates.
Due to the competitive nature of Italian ryegrass, it is essential to control this weed prior to planting corn. Clethodim must be applied at least 30 days prior to planting corn. If the clethodim application for Italian ryegrass was not timely, then corn planting may have to be delayed to avoid crop injury.
Most people consider corn to be one of the more competitive crops. It usually emerges quickly, grows rapidly, and shades the middles in a much shorter time than cotton or soybeans.
A general rule is that if corn can be maintained weed-free for the first four to five weeks after emergence, then there will be no effects on yield due to weed competition; however, this rule applies to weeds that emerge at the same time or following corn. It does not apply to Italian ryegrass, which is usually 12 to 24 inches tall during corn planting season in the Mississippi Delta.
When corn is planted into standing Italian ryegrass, the aboveground parts of Italian ryegrass will reduce the light and space available to developing corn seedlings while ryegrass roots will limit the water and nutrients that can be taken up by corn.
Another motivation for controlling Italian ryegrass prior to planting is the lack of over-the-top herbicide options available in corn. Some ALS inhibitors (Accent, Resolve, Steadfast, and Stout) labeled in corn have activity on Italian ryegrass. Unfortunately, Italian ryegrass is resistant to ALS-inhibiting herbicides in 13 counties in the Mississippi Delta, rendering this chemistry ineffective for ryegrass control in many areas. Therefore, it is imperative to control all Italian ryegrass before corn is planted.
For corn, a spring burndown program for glyphosate-resistant Italian ryegrass should begin with clethodim (12 to 16 ounces of Select Max or 6 to 8 ounces of 2-pound clethodim formulation) applied not less than 30 days before planting.
Italian ryegrass that escapes the early burndown application of clethodim should be treated with paraquat (3 to 4 pints of Gramoxone Inteon or 2 to 2.67 pints of 3-pound paraquat) plus atrazine (1 quart) before corn emerges.