By William Curran and Dwight Lingenfelter

In last year’s April 10 Field Crop News, we had an article about cover crop management.

The first sentence last year started out “with the warm dry weather we have been experiencing this spring, cereal grain cover crops and weeds are ahead of normal...

So, this year we start out “with the delayed winter and cool spring, much of the cereal rye or other small grain cover crops are slower taking off this spring than in the past”. Wow, what a difference a year makes! 

The end result is that don’t get too eager to kill those cover crops this spring until they are actively growing and hopefully have contributed some benefit to soil quality and the subsequent cash crop.  Here are some reminders:

  • Herbicide rate—most glyphosate labels recommend increasing the rate of product as the cereal grain and weeds mature. This is just as important under cool-cloudy conditions like we have been experiencing. With Gramoxone, use the 3 pt rate and remember that it is better on smaller cereals or after they have reached the boot stage—during the period of rapid culm elongation it is less effective.
  • Include appropriate adjuvants in the spray tank—include 1 to 2 qt/100 gal nonionic surfactant (unless fully loaded formulation) plus 8.5 to 17 lb/100 gal AMS or equivalent with glyphosate. The AMS helps alleviate hard water problems and also can reduce antagonism if tank-mixing with other herbicides such as 2,4-D.  Be sure to add the AMS first to the spray tank and agitate before adding the glyphosate.
  • Use a clean water source that does not contain soil or other sediment that can reduce glyphosate or Gramoxone activity.
  • Use flat fan nozzle tips that produce a uniform spray pattern and thorough coverage.
  • Spray in sufficient carrier to achieve good coverage (usually between 10 and 30 GPA).
  • Make sure the sprayer is accurately calibrated (output, pressure, pattern, speed, etc.) to deliver the appropriate rate uniformly.
  • Air temperature before, during, and after application can influence control. Cold nights (<40 F) will reduce activity, particularly for glyphosate, and especially when followed by cool (<55 F) cloudy days.
  • The more time between application and rainfall the better, especially with difficult to control perennials.

Annual ryegrass (Lolium multiflorum) cover crop control - Historically, annual ryegrass can be somewhat difficult to control with herbicides in the spring.  Some general recommendations for control of annual ryegrass are provided by a team of agronomists from Illinois, Indiana, and Oregon State who have a lot of experience with this species. 

Click here for their complete management guidelines for ryegrass management in corn and soybean production.  For control, some general take home points:

  • Control is best done when the plants are small, 8 inches in height and before the first node has developed.  This is usually late March to early April in the lower Corn Belt and mid April in the northern Corn Belt – adjust accordingly this year
  • While one burndown application may provide control of annual ryegrass, growers should plan for two.  
  • If annual ryegrass is allowed to reach the flowering stage, the control of the plant is easier, but some viable seed may develop and may create additional weed management problems in the future.
  • For glyphosate, successful control depends on timing, application rate, and weather conditions.  Apply glyphosate at 1.25 to 1.5 lb ae/acre (48 to 64 fl oz of a 3 lb ae gal product) with AMS and surfactant.  Some folks add an acidifier (e.g. citric acid) to improve performance.  Add AMS and other additives to the spray tank, agitate, and then add the glyphosate.  Adding other herbicides to glyphosate and especially triazines or clay-based materials can antagonize glyphosate activity.  Generally,  including 2,4-DLVE  in the mixture doesn’t appreciably reduce activity and it can help broaden the weed control spectrum.
  • The use of air induction spray tips that produce coarse droplets should be avoided and for glyphosate, reduce spray application volume to 10 GPA (others recommend a bit higher carrier volume if the stand is thick and coverage is a concern).
  • Spray during daylight hours at temperatures about 60F and when annual ryegrass is actively growing.
  • If night temperatures drop below 38F, wait three days before spraying and soil temperatures should be above 45F.
  • Spray at least 4 hours prior to sunset to allow for maximum translocation.