Control of Annual Ryegrass when Used as a Cover Crop in the Midwest

Annual ryegrass is a vigorous, cool-season grass and a valuable cover crop for corn and soybeans in the Midwest. Controlling annual ryegrass in the spring with glyphosate or other herbicides depends on:

• Using full herbicide rates
• Spraying during favorable weather conditions
• Using good spraying practices.

Controlling annual ryegrass in the spring is best done:

• In warm weather
• When the ryegrass is actively growing.

Annual ryegrass can be a challenge to control if the herbicide is applied when:

• There is cool, cloudy and wet weather, or
• When the ryegrass has reached the joint growth stage (stem elongation).

The following are guidelines for controlling annual ryegrass, based on over 20 years of field testing and farm experience in the Midwest.

Timing

Control (burndown) of the annual ryegrass cover crop:

• Is most successful when the plant is small, 4-8” in height
• Annual ryegrass is more difficult to control after the first node has developed
• Burndown occurs in late March or early April, or mid-April in the northern Corn Belt.

In the spring (if planted the prior year) annual ryegrass is already well established (7-8 months) and has an extensive root system. It should be treated like established tall fescue or smooth bromegrass, not like a seedling grass. It is important to not let the ryegrass go to seed or it may create additional weed management problems.  If annual ryegrass is allowed to reach the flowering stage, control is easier, but some viable seed may develop.

Spray coverage

Make sure you have thorough spray coverage:

• Medium spray droplet size and moderate spray pressure is recommended
• Standard or XR flat fan nozzles are the nozzles of choice for most applications
• Don’t use flood jet or air induction nozzles (with coarse droplets)

However, air induction nozzles which produce a medium spray droplet size are suitable and aid in drift control. Make sure spray pressure is adequate (generally higher than a standard flat fan) and nozzle overlap is 100% when using these nozzle types.

Reduce spray application volume to 10 gallons per acre. Use only the amount of water you need to achieve good coverage. Spray volumes below 7 gpa and above 15 pga may reduce the effectiveness of glyphosate for grass control.

Glyphosate burn down applications 

Glyphosate is the most common herbicide used to control annual ryegrass. It’s very important to use a rate that is adequate. The minimum rate of glyphosate recommended for annual ryegrass is 1.25-1.50 lb a.e./acre with ammonium sulfate and surfactant in late March to early April. Use 1.75 lb a.e./acre if needed.

Glyphosate products vary in concentration and this affects application rate. Here are two application examples to provide the necessary 1.25-1.50 lb/acre a.e.:

• A 41% glyphosate product containing 3 lbs/gal of a.e. (acid equivalent). Application rate should be 53-64 oz/acre
• Roundup PowerMax is a 48.7% glyphosate product with 4.5 lb/gal of a.e. Application rate should be 36-43 oz/acre

While one burndown application should provide control of the annual ryegrass, growers should plan for two applications, especially if the initial spray conditions were cool

• Consider using an herbicide with a different mode of action if re-spraying is needed (Research is currently testing alternatives to glyphosate and tank mixes with glyphosate to reduce the dependence on this important herbicide)

Even when annual ryegrass is small it requires full rates of herbicides to achieve control. Low rates will often stress the plant making it more difficult to control at a later date

• In years with marginal weather conditions, or where the ryegrass is in the jointing stage, use a higher rate of glyphosate (1.75 lb a.e./acre) to help insure complete control. Using a full label rate once is preferred to split applications of a lower rate.

Water

The quality of the spray water is important.  Water sources that are high in minerals, clay, or organic matter will interfere with or tie up the glyphosate and reduce its effectiveness. Test your water source and treat accordingly. Make sure the pH of the water is within the range that is optimum for glyphosate.  Follow label directions carefully with respect to pH and mixing order:

• Add ammonium sulfate (AMS) to all glyphosate products unless the product label says not to
• It is important when adding AMS, pH buffering agents, water softening agents, or citric acid that they be added to the full spray tank of water and agitated for 3-5 minutes before adding the glyphosate.  This is to ensure that the calcium, magnesium, iron and other dissolved minerals in the water do not interfere with glyphosate activity
• Additional NIS surfactant (0.25% v/v) may be needed for some generic glyphosate products, and should be added to the tank after the glyphosate
• Add 8 oz/acre of 2,4-D to help control winter annual broad leaf weeds or clover.
• Crop oil concentrate should not be used.

Weather conditions

Weather conditions can effect how well glyphosate controls annual ryegrass. If it’s sunny but still cold, for example, it’s usually better to be patient and wait until the crop is actively growing and temperatures are more favorable for burndown:

• Annual ryegrass should be actively growing (5-7 days) for best results
• Spray during daylight hours. Minimum daytime temperatures should be 55^oF. Above 60^oF is optimum
• Temperatures at night are also important. If night temperatures drop below 38^o F, wait three days before spraying. There should be at least 3 nights above 40^oF
• Soil temperatures should be above 45^oF
• Spray at least 4 hours prior to sunset to allow for maximum translocation of the glyphosate within the plant.

Corn production

• Never tank-mix atrazine or Callisto (mesotrione) with glyphosate or annual ryegrass control can be reduced as much as 40%.  Atrazine can be applied 14-21 days after glyphosate application
• Adding Princep (simazine) improves weed control but may be a concern on sandy soils
• Adding Princep, Balance Pro, Prowl H₂O, ResolveQ or Basis Blend, 2,4-D, or Axiom (flufenacet + metribuzin) at full label rates has shown good activity for general weed control. Field trials have not shown any antagonisms between glyphosate and Axiom with regard to control of ryegrass
• Full rates of Liberty (glufosinate-ammonium) and Gramoxone (paraquat) have provided 70-85% control of ryegrass before nodes are formed and less control after the 1-2 node stage.  Two applications of these products 3 weeks apart (allowing for regrowth and retillering) have provided much better control
• After the crop emerges, escapes can be controlled in corn with labeled rates of Accent Q, Steadfast Q, or Option, but best control is obtained with these products when temperatures are above 70 degrees
• Glyphosate can be used in Roundup Ready crops.

Soybean production

The use of Roundup Ready soybeans makes controlling an annual ryegrass cover crop much easier. However, in conventional soybean production or after the soybean crop emerges, escapes can also be controlled with additional modes of action by applying full rates of:

• SelectMax (clethodim), Poast Plus (sethoxydim), or Fusilade DX (fluazifop)
• Make sure to use fertilizer and surfactant or crop oil concentrate per label instructions. These products have shown some problems if applied in cold temperatures
• Assure and Poast, especially in cooler weather, have shown very poor control.

For More Information

(Click here) for a handy 1-page flyer about general control of ARG.

(Click here) for a longer paper by Purdue University Extension.

Winter wheat production –   (Click here) for a flyer on control of ARG  in wheat

• ARG can be a very competitive weed in winter wheat
• Apply a glyphosate burn down before planting wheat
• Essential to spray a post-emergence grass herbicide like Osprey, Axial XL, or PowerFlex in late winter or early spring – check plant back restrictions.

Mention of any product does not constitute any type of endorsement or guarantee.