By Travis Legleiter
Each year, ryegrass burndown prior to no-till corn and soybean seems to get more difficult and complaints of glyphosate failure continue to increase. The conundrum of this situation is that only about a third of ryegrass samples sent to the University of Kentucky Herbicide Resistance Screening Program are confirmed glyphosate-resistant. While we know glyphosate resistance in ryegrass is occurring in select populations in Kentucky, it appears that, in many cases, our glyphosate burndowns are failing for reasons other than resistance. Here today, we hope to tackle potential pitfalls causing burndown failures on ryegrass.
Pay Attention to the Weather
Springtime weather can be volatile with both warm days and cold nights. When applying burndown applications to ryegrass, it is important to pay attention to nighttime temperatures. We have found that when nighttime temperatures 2 days prior to or after dip below 40-45 F, failures are more likely to occur during application. The key window is to find when nighttime temps remain above 40F, the soil conditions allow for sprayer traffic, and ryegrass remains small.
Apply 1.5 lb ae glyphosate
When I receive a complaint about a ryegrass burndown failure with glyphosate, one of the first questions I ask is how much glyphosate was applied. The majority of the time, the rate is around 0.75 to 1 lb ae glyphosate per acre. Our research has consistently shown that applying 1.5 lb ae glyphosate per acre is required to achieve optimal control, as shown in Figure 1.
How much is 1.5 lb ae glyphosate? Glyphosate comes in many formulations, with varying glyphosate loads and salts used to stabilize the active ingredient in the jug. Because of this, we often refer to glyphosate rates in lb ae (acid equivalent) per acre rather than fl oz of product per acre. The following table lists the majority of available glyphosate products and the fl oz rate required to achieve glyphosate rates of 0.56 to 1.5 lb ae/A. This table can also be found on page 17 of AGR-6.
Source : uky.edu