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Having trouble with Italian ryegrass?

Research shows that application issues, not glyphosate resistance, is a big issue at burndown.

April 18, 2024

2 Min Read
A field of ryegrass
BURNING IT DOWN: Italian ryegrass can be particularly tricky to manage this time of the year, so it’s important to time your glyphosate applications correctly and burn it down at the height. Courtesy of Kurt Vollmer

by Kurt Vollmer

Italian ryegrass has been giving producers trouble the past couple of years.

There have been several reports of ryegrass control failures following glyphosate applications in the spring. Last year, seeds from 49 ryegrass populations from Maryland and Delaware were screened for glyphosate resistance at Caio Brunharo’s lab at Penn State.

Out of 40 populations screened, all were controlled by glyphosate at 2 pounds an acre. This shows that recent troubles controlling ryegrass may be because of application issues rather than glyphosate resistance.

Italian ryegrass can be particularly tricky to manage this time of the year, so it’s important to remember the following:

  • Cold weather affects glyphosate uptake and translocation. Applications should be made when the temperature is greater than 55 degrees F and consistently remains above 45 degrees for three to five days to be effective.

  • Higher rates will be needed to control ryegrass compared to other species — 1.25 to 1.5 pounds an acre.

  • Plants should be less than 6 inches tall, but no more than 8 inches tall, at the time of application.

Other components in the tank can also affect glyphosate performance.

Include a spray-grade ammonium sulfate — 8.5 to 17 pounds per 100 gallons — in the tank to abate water quality issues. UAN and high rates of triazine herbicides — greater than 0.25 pounds an acre — such as atrazine that are included in the tank can also reduce glyphosate absorption and translocation.

If glyphosate alone fails, try tank-mixing or alternative herbicides. Last year at the Lower Eastern Shore Research and Extension Center, the researchers achieved 98% ryegrass control with glyphosate at 1.25 pounds an acre, plus clethodim at 0.121 pounds an acre, plus nonionic surfactant at 0.25%, plus AMS at 8.5 pounds per 100 gallons.

They also saw good control with sequential applications of paraquat at 1 pound an acre, plus crop oil at 1%, plus AMS at 8.5 pounds per 100 gallons made 14 days apart.

In trials conducted in Pennsylvania, glyphosate, plus 0.02 pound an acre of rimsulfuron, also controlled ryegrass at greater than 95%.

Always consult the label for important information such as tank-mixing and plant-back intervals before applying any pesticide.

Vollmer is an Extension specialist of weed management with University of Maryland.

Source: University of Maryland Agronomy News

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