Annual ryegrass: A great cover crop, but can we control it?

Michigan farmers are increasing their use of annual ryegrass as new varieties have been released.

In the last several years annual ryegrass (AR) has become a popular cover crop in the Midwest. It has most often been used in no-till farming systems in Indiana, Illinois and Ohio. Michigan farmers have increased their use of annual ryegrass as new varieties have been released.

The root system for AR is massive and can grow up to three times deeper than its top growth. In other words, 10 inches of above ground growth can result in 30 inches of root growth. The fibrous root system for annual ryegrass can really enhance soil quality. When properly killed annual ryegrass is a great cover crop.

Unfortunately, annual ryegrass can be difficult to kill. In 2012 the “Michigan Soybean Promotion Committee” provided funding for the MSUE cover crop team to evaluate controlling annual ryegrass prior to planting no-till soybeans.

The best results for controlling annual ryegrass have been when annual ryegrass is actively growing and the air temperature is above 60° Fahrenheit. In March of 2012 we had a heat wave where temperatures were in the 80’s for an extended period. This did stimulate annual ryegrass growth however; we did not try to control annual ryegrass at this time.

Our study is looking at applying four different herbicide treatments at three different growth stages of annual ryegrass. These include annual ryegrass at: 6-8 inches, 10+ inches and after planting. Due to a cool spring, the best environmental conditions for controlling annual ryegrass were difficult. We actually had our best control of annual ryegrass when it was over 12 inches tall. We had better control of annual ryegrass on our higher sandier ground as compared to the lower high organic matter locations. I have included some pictures of the higher glyphosate treatment with ammonium sulfate.

I have also included a picture of the lower Glyphosate rate and poor annual ryegrass control.

Annual ryegrass
Annual Ryegrass (AR) controlled with Roundup PowerMax™ at 32 oz/A plus Ammonium Sulfate (AMS) at 17 lbs/100 gallons of water. Annual ryegrass was 10 inches and the temperature 65° Fahrenheit on May 3rd 2012. Soybeans were no-till drilled at 180,000 seeds/acre.

Annual ryegrass
Annual ryegrass was sprayed with Roundup PowerMax™ at 32 oz/A + AMS 17 lbs/100 gal. water after no-till drilling soybeans at 180,000 seds/acre on May 10th 2012.

Annual ryegrass
Annual ryegrass was sprayed at lower rate of Roundup PowerMax™ at 22 oz/A + AMS on April 13th, 2012. The annual ryegrass has regrown and has become a weed.

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