By Blake Jackson
Controlling ryegrass ahead of no-till corn and soybean planting has become increasingly challenging, with many growers reporting glyphosate failures. However, according to University of Kentucky Extension Weed Specialist Travis Legleiter, only about one-third of ryegrass samples tested show true glyphosate resistance. This suggests that application issues, rather than resistance alone, are often responsible for poor control.
Weather conditions play a major role in burndown success. Spring temperatures can fluctuate widely, and cold nights are particularly problematic. Applications made when nighttime temperatures drop below 40-45°F within two days before or after spraying are more likely to fail. For best results, apply herbicides when nights remain above 40°F, fields are accessible, and ryegrass is still small.
Application rate is another critical factor. Many failures occur when glyphosate is applied at just 0.75 to 1.0 lb acid equivalent (ae) per acre. Research consistently shows that 1.5 lb ae per acre is needed for effective control. Because glyphosate formulations vary, rates should be measured in acid equivalent rather than fluid ounces. Adding 1% v/v methylated seed oil (MSO) has also been shown to improve results.
Some applicators turn to clethodim after glyphosate fails, but this is not recommended in early spring. Cool temperatures reduce its effectiveness, and overuse can promote resistance. In addition, clethodim carries a 30-day plant-back restriction for corn, which must be followed to prevent residue issues.
In confirmed cases of glyphosate resistance, growers should consider using paraquat combined with atrazine for corn or metribuzin for soybean. While these mixtures improve control, they may still require a follow-up application. Implementing fall herbicide programs can also help reduce ryegrass pressure in the following season.
Photo Credit: gettyimages-klosfoto
Categories: Kentucky, Crops, Corn, Soybeans