The Chemistry of Burndown of Annual Ryegrass

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.

 

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