There are so many articles on bad weeds that I went through old articles and found one called “The Five Worst Weeds” that was in the Star Tribune in 2011.
I don’t think the list has changed much, but some have been added. The number one weed was wild parsnip, and there was an article in local papers this summer about it. The flowers of wild parsnip are yellow, looking similar to a yellow version of Queen Anne’s Lace or carrots. The main reason why this weed is so dangerous is the severe reaction of the weed when it comes in contact with skin.
I’m going to add poison hemlock because all parts of this weed are very poisonous. An article by MDA warns that not only does contact with the skin cause the same problems as wild parsnip, but if animals digest the weed it could be deadly. Purple blotches on the stem of hemlock distinguish it from wild carrot and parsnip. The only good news is that hemlock has not yet taken over unplowed fields and ditches as wild parsnip has.
The Tribune’s number two bad weed was yellow starthistle; at the time of the article it was not yet a problem in Minnesota. Now it is expected to displace many of our native plants if and when it arrives.
The third bad weed is Japanese knotweed. This shrub-like perennial has hollow stems and small white flowers that bloom in clusters in August and September. Since they can grow to a height of six to eight feet tall it is feared they will shade out native vegetation and invade the habitat of local fish and wildlife.
Number four is oriental bittersweet. Very similar to American bittersweet, it climbs on trees and other structures. It is easy to identify in the fall, with yellow fruit capsules that cover the stem.
The last weed is narrow leaf bittercress. This low-growing weed lives for 2 years. The first year it has larger leaves shaped like a catcher’s mitt. The second year it produces narrow leaves and four-petaled white flowers. A single plant can produce up to 5,500 seeds. First reported in Minnesota in 2008, this European plant import displaces native plants in forests and is beginning to invade rivers and forestland near the St. Croix and Mississippi rivers.
I realize this article was written some years ago, but if you are interested in these bad weeds, go to www.mda.state.mn.us/en/plants.aspx.