While it may look like a beautiful, yellow dandelion-like flowering plant, narrowleaf hawksbeard is an invasive noxious weed moving rapidly into Montana and North Dakota.
Shelley Mills, Montana State University Valley County Extension agent in Glasgow since 2010, said hawksbeard was brought into Montana on contaminated alfalfa seed, with the alfalfa being grown on 400 acres.
“Hawksbeard seed is difficult to clean out from the alfalfa because the seed is so tiny,” Mills said.
Hawksbeard will germinate in the fall as a winter annual, overwinter and bolt in the spring. But it can also germinate in the spring and become a summer annual.
“I have seen it germinating anywhere from March all the way through November, and it germinates in soils that are 41 degrees, way before our wheat will germinate,” Mills said.
Normally, hawksbeard blooms on July 4, but with the drought of 2017, it was blooming in early June last year.
The weed comes from Siberia, and does well in the Montana/North Dakota climate.
Mills heard about the weed the first year she worked for Valley County.
“In 2010, one of the growers in my county came in with this lovely yellow plant and said, “‘Okay, I am putting on 64 ounces of glyphosate. How come I can’t kill this plant,” Mills said.
Mills contacted Brian Jenks, North Dakota State University weed specialist, and Ed Davis, MSU weed specialist, to find out what could be done about narrowleaf hawksbeard.
They told her the weed has been found in northwestern Montana, eastern Montana and was recently found in northwestern North Dakota. It has also been found in Saskatchewan and Minnesota.
Mills spotted hawksbeard last year in Circle and Big Sky, Mont., as well.
“Hawksbeard is a really tenacious plant and it is moving quickly,” she said. “We need to get after it now.”
Mills found out from the scientists that two applications of glyphosate are needed to control the weed – along with another mode of action.
“The best way to control it is a fall glyphosate application, followed by a spring application of glyphosate mixed with another mode of action,” she said.
If a producer is going into wheat that has been invaded by hawksbeard, he should use 21 ounces of glyphosate mixed with some other product that has some residual in it or a different mode of action.
“This is your chance to control the weed in wheat, but in wheat, you also need another mode of action like Gold Sky, besides just the glyphosate,” Mills said.
The plant produces from 3,000 to 50,000 seeds per plant, and reproduction happens from seeds only. Seeds can be spread from wind, in hay, on machinery, or in contaminated seed.
“If we can stop the seed production, we can get a handle on it,” she said.
Mills explained she was in northern Valley County and saw an entire 400-acre field that was completely yellow last year.
“I have seen it in flax where the crop was suppose to be blue, but it was overrun with yellow narrowleaf hawksbeard. It can get out of hand very rapidly,” she said.
For pasture and range lands, a pint of 2,4-D may be sprayed while the forbs and alfalfa are dormant in late fall and early spring.
Once hawksbeard has bolted, herbicides are less effective.
With pulses and sugarbeets, producers should use straight glyphosate in the fall. That can be followed in spring with 21 ounces of glyphosate, tank-mixed with Sharpen.
“Sharpen is the only control you have in pulses,” Mills said.
Valor is a new product that may soon be labeled for hawksbeard.
Hawksbeard does not like tillage, but if a producer tills and it rains, the weed comes back up again.
“If you think you have narrowleaf hawksbeard or any resistant weed, contact your Extension service or weed board,” she said. “Definitely call us if you put something on and it doesn’t kill it. We want to know about it.”