Glyphosate-Resistant Ryegrass Confirmed In Oregon Testing

Researcher recommends no-tillers keep a wary management eye on the increasingly popular cover crop, already tough to control with glyphosate

Test results from two sites in the Pacific Northwest confirm the development of glyphosate-resistant Italian ryegrass.

Weed scientist Jed Colquhoun of Oregon State University reports that glyphosate-resistant ryegrass has been found at two orchards in Oregon and several other suspected sites are being tested.

The news comes as annual rye grass is gaining popularity because of its uncommonly deep, fast-growing roots and an early burndown that leaves a wide window for no-till crops. (See “Emerging Trends,” No-Till Farmer, March 2005, Page 13.)

One And The Same

The Italian ryegrass found to be glyphosate-resistant is the same species, Lolium multiflorum, as the annual ryegrass favored by no-tillers, 
Colquhoun says.

“When acting as a weed, the species is referred to as Italian ryegrass. Italian ryegrass is a common weed in many 
cropping systems in the Pacific Northwest and nationally,” he says.

It is also a commercial product in the region, with annual ryegrass seed produced for use as a cover crop elsewhere in the United States.

However, Colquhoun notes, “We have tested several commercial annual ryegrass varieties. We found no resistance to glyphosate in these varieties,” meaning there is little risk of no-tillers purchasing resistant ryegrass seed.

Producers Prepared

Bryan Ostlund, spokesman for the Oregon Ryegrass Commission, a trade group representing ryegrass producers, describes the resistant ryegrass as “isolated pockets” that resulted from growers “spraying glyphosate, year after year,” without an adequate weed management plan that includes alternative herbicides.

Ostlund says ryegrass producers routinely use glyphosate to clear their fields, but they…

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