OSU works to delay glyphosate resistance in Russian thistle

Barroso collects Russian thistle
Weed scientist Judit Barroso collects Russian thistle in eastern Oregon.

Weed causes serious crop production problems in dry-land sall grain producing areas

In the fall of 2015, farmers in northeast Oregon reported difficulties in controlling Russian thistle with glyphosate, one of the most widely used herbicides in the United States. The following February, OSU researchers randomly collected 10 Russian thistle populations on fallow fields in Umatilla, Morrow and Sherman counties.

Lab testing of the samples showed that three of the collected populations in Morrow County were glyphosate-resistant. Those three populations were likely treated with glyphosate much more often than the plants that were susceptible to the herbicide, said Judit Barroso, a weed scientist at OSU.

Russian thistle, also known as a tumbleweed, causes serious crop production problems in dryland small-grain producing areas in the United States, costing farmers more than $50 million annually in control measures. Farmers in the arid region of northeastern Oregon rely on repeated applications of herbicides such as glyphosate to control Russian thistle.

Glyphosate is the herbicide of choice for growers in the Pacific Northwest to control Russian thistle after harvest and in summer fallow.

Barroso is working with growers to delay the glyphosate resistance in Oregon by rotating different herbicides and using other weed control practices.

“There needs to be an immediate transition to a more diversified approach for control of this troublesome weed species,” she said.

Russian thistle breaks off the stem when it dies and moves with the wind. As a tumbleweed, it can spread seeds over long distances, which may allow the glyphosate resistance to spread very quickly. Each plant, growing without competition, produces more than 50,000 seeds.

Source: Judit Barroso, OSU Extension specialist


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