Jed Colquhoun – Oregon State University
Reprinted from Crop and Soil Newsnotes, OSU Extension, May 2005
Background:Italian ryegrass that is resistant to the herbicide
glyphosate was confirmed in 2004 in Oregon, and plants from
several other suspect sites are currently in resistance testing. Herbicide
resistance is the ability of a plant to survive an herbicide application
that in the past controlled that species. Herbicide resistant Italian ryegrass
is most likely to occur where glyphosate has been used repeatedly over
several years, such as in long-term perennial crops (tree fruit and nut
production, vineyards, etc.) or non-cropland. Given that glyphosate resistance
is a recent occurrence in Oregon, and no glyphosate resistance has been
observed in grass seed production, rapid response and appropriate resistance
management strategies are encouraged to prevent further resistance development.
Strategies to reduce the risk of resistance Italian ryegrass:
1. Rotate weed control strategies and herbicide site of action. Avoid repeated applications with the same herbicide site of action within a growing season. Don’t retreat surviving plants with the same herbicide. Consider all potential weed management strategies.
2. Don’t allow weedy Italian ryegrass to reproduce and spread pollen or seed. Clean all equipment when leaving a site with suspected resistant plants.
3. Keep an eye out for survivors and remove them prior to flowering and reproduction.
4. Plant weed-free annual ryegrass seed.
Consider the following questions if glyphosate resistant Italian ryegrass is suspected:
1. Is it only Italian ryegrass that survived herbicide application, or are other species that are normally susceptible to glyphosate also not controlled? Multiple species surviving an herbicide application often suggests reasons other than resistance for poor control.
2. Is there an obvious pattern, such as a sprayer skip or poor herbicide coverage that could explain weed control failure? Weed resistance often occurs in irregular patches where seed spread from a plant that survived a previous herbicide application.
3. Are there herbicide symptoms on the surviving plants? Resistant plants often, but not always, show no symptoms related to the herbicide application.
4. Is there a record of repeated glyphosate use, and has the rate required for adequate control increased over time?
What should you do if you suspect resistance?
· Contact University researchers or local Extension faculty so that they can collect samples and test for resistance.
· Immediately consider alternative control strategies to keep the problem from getting worse. Resistant plants will not become susceptible, but further selection for resistance can be reduced.
Secondary content using h2 tag.
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
Heading using the h3 tag
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.