For cover crops that overwinter, termination can be a challenge. In fact, fear of a runaway stand concerns many growers..

Cereal rye – a tall grain – can grow several feet tall in just a few weeks if spring conditions are conducive. Annual ryegrass, a shorter plant that is actually no relation to cereal rye, has a hardy root system and a reputation for being tough to kill.

 Both are susceptible to glyphosate, notes Jamie Scott, a cover-crop seed dealer who plants cover crops on nearly all of the 2,000 acres of corn, soybeans and wheat he farms near Pierceton, Ind. However, he warns, early spring is a tough time to work with Roundup.

“Glyphosate is made for 70-to-80-degree weather,” Scott says. “We’re using it at 50 degrees. We have to learn how to help it out.”

The first step is to make sure the cover crop is actively growing. The plant needs to pump nutrients through its system to translocate the herbicide. Avoid applying glyphosate when nighttime temperatures fall below freezing.

Spray in the morning or right after lunch to give the glyphosate several hours to translocate through the plants, Scott advises. “We’ll do one or two loads after noon, but not much more than that – and nothing in the evening,” he says of his own operation. “It takes four or five hours of sunlight to translocate the glyphosate.”

Pushing glyphosate to its limits of temperature and timing means there’s no room to skimp on carrier, Scott adds. He recommends 10 to 12 gallons of water, conditioned if necessary to avoid tying the herbicide up with the ions in hard water.

“Keep it simple that first year,” Scott explains. “That’s normally where we get into trouble. Someone wants to add 28% or some product somebody sells them that’s supposed to help. It may or may not be the problem, but it makes it hard to troubleshoot.”

The Oregon Ryegrass Commission points out that annual ryegrass is more difficult to control after the first node has developed. That’s a reminder that a springtime stand of annual ryegrass is made up of mature plants, not seedlings. With its well-established root system fighting for life, annual ryegrass requires excellent foliar coverage with a full rate of herbicide for control. Medium-sized droplets, moderate spray pressure and careful application help give glyphosate the edge it needs.

Not every mix works with glyphosate, though. The Oregon Ryegrass Commission website says that tank mixing atrazine or mesotrione with glyphosate can significantly reduce burndown.