Tips to kill rye covers in asparagus during a cold spring

Now that it finally feels like spring, one job on asparagus growers’ minds is terminating your rye cover crop. Glyphosate is our tool of choice for terminating rye cover crops. Remember, it needs to be translocated to the growing point of rye, which means rye needs to be actively growing to achieve a good kill. While sunny days and warmer air temperatures will lead to a green up of rye leaves made last fall, remember that the growing point of rye is below ground in early spring. This means that waiting until both soil and air temperatures warm will help ensure a good kill of your rye with glyphosate.

How warm does it need to get to obtain a good rye kill? Up until early this week, soil temperatures have been cool and nighttime temperatures have been below or near freezing. Bernard Zandstra, MSU Department of Horticulture, suggests waiting until it stops freezing at night. A week above freezing should result in active growth and better herbicide activity. Thankfully, the forecast calls for warmer temperatures Sunday, April 29, through early next week. Experience suggests that adding ammonium sulfate can help improve kill of your rye with glyphosate.

Since we are rapidly approaching asparagus harvest season, you can also consider applying pre-emergence herbicides at the same time as glyphosate. This will save a pass over the field and could help given some of our pre-emergence herbicides have a 14-day (Tricor, Solicam, Spartan, Prowl H20, Command) or 16-day pre-harvest interval (Dual Magnum). Experience suggests that with the right adjuvant and glyphosate rates, this should not compromise rye control.

Growers don’t always have time to wait for ideal conditions. What can you do if your rye escapes control with glyphosate? One option is apply a grass killer to clean up escapes. These include:

• Fusilade (active ingredient fluazipop-P, use with non-ionic surfactant or crop oil)
• Poast (active ingredient sethoxydim, use with crop oil)
• Select Max (active ingredient clethodim, use with a non-ionic surfactant)

These selective grass killers have a one-day pre-harvest interval.

– Ben Werling, Michigan State University Extension, and Bernard Zandstra, MSU Department of Horticulture