While Canada thistle and leafy spurge have long been the focus of ranchers and weed control officers in the state, recent years have seen the rise of absinth wormwood infestations across the state something the North Dakota Agriculture Department would like to see an end to.
A perennial flowering plant with a strong sage odor, absinth wormwood appears grayish in color and usually grow to about 3 feet tall. Because of the plant's ability to reproduce by its roots or through the thousands of seeds it produces each year, the weed can rapidly infest pasture and rangeland, and can be found in concentrations near roads, shelterbelts and any other areas where ground has been disturbed.
"Weed officers and producers are telling us that they are seeing more and larger infestations of absinth wormwood, especially in western North Dakota," said Ag Commissioner Doug Goehring. "There have also been reports of this plant being sold at some local retail locations in the state."
Although the 2008 weed survey showed roughly 54,000 fewer infested acres than 2007, the 554,175 acres reported are well above levels seen throughout the 2000s, causing many to take action.
As with the rest of the state, Ward County has seen a substantial increase of absinth wormwood infestations in recent years, from 1,836 acres in 2003 to an estimated 2,900 acres this year.
"I think a lot of the increase here has to do with the new construction of little 10-acre farmsteads going up all over. Those people need to be aware that it's their responsibility to take care of their little piece of heaven," said Ward County weed officer Derrill Fick. "It doesn't take much for it to spread, it can grow in any soil type and the seeds are so fine that many people won't notice them. If homeowners don't take care of it, it could easily spread back to the surrounding farms that were controlling the problem before."
Brian Jenks, weed scientist at the North Central Research Extension Center, said the weed is most troublesome in pastureland where cattle are grazing because it reduces grazing capacity by crowding out forageable grasses and can also taint milk if consumed by dairy cattle, causing additional income loss to producers.
Although several herbicides exist to treat the problem, Fick said many need a restricted use license to buy and apply the products. For the average homeowner, he suggests the herbicide Milestone, which is very effective at a low application rate, does not leave any residuals and can be purchased by anyone.
As for applying the herbicide, Fick said the best time to treat the weed is before it reaches the bud stage but it will still be effective if sprayed at a later stage.
While Canada thistle, leafy spurge and absinth wormwood are the top invasive species in Ward County and the state, weed experts in the county are looking at two other potential problems.
"Spotted knapweed has been coming along in recent years, especially in rural construction sites," Fick said. "The problem with this species is that it's a biennial plant, so you got to hit it at the right time. If you can get it at the rosette stage you can control it pretty well, but if you miss then you have to wait until the next year."
A fraction of the top three invasive weeds, spotted knapweed has still posted a substantial increase in recent years from 26 acres in 2003 to 43 acres in 2006 before falling slightly to 38 acres in the 2007 survey.
Another potential problem - yellow toadflax.
"Leafy spurge used to be a big problem out west of Burlington but after releasing flea beetles a few years ago the acreage has dropped," Jenks said. "That's good news, but the problem now is that yellow toadflax has moved in to take its place and we don't have a biological control like that available. We have a product in testing now and so far it looks promising, but it won't be available for at least two or three years and a lot can happen between now and then."
