As early as 1895, Minnesota has had laws to prevent invasive weeds from taking over our yards, parks and forests. In 2009, an advisory board was put together to help the Minnesota Department of Agriculture update the list of noxious weeds and devise ways to categorize them. The goal is to stop the spread of these aggressive weeds that threaten our wildlife, native plants and, in some cases, even our health. I asked the advisory board which weeds were the worst of the worst. They came back with a list that included weeds we've known -- and hated -- for years, and weeds that are just starting to appear in the state. Some are so new to Minnesota that the Ag Department is still trying to figure out how widespread they are and what kind of damage they may do. Read it and weed:1. Wild parsnip
This perennial weed has many small yellow flowers that appear in a flat cluster at the end of a flower stalk that looks a bit like Queen Anne's lace. It's easiest to identify when its flowers start appearing, usually around June.
This invader from Europe and Asia has gotten a strong foothold in Minnesota, growing in fields, prairies and along roadsides. In addition to displacing native plants, it can cause burns if the sap comes in contact with your skin.
2. Yellow starthistle
An annual with stems covered in distinct woolly hair, starthistle is topped by yellow flowers that look like spiky dandelions. It thrives in sunny locations, such as fields and grasslands, and typically grows to 1 to 2 feet tall.
Although it hasn't been found in Minnesota yet, it's expected to displace many of our native plants if it arrives. If you see this plant, report it to the Agriculture Department's Arrest the Pest hot line, 1-888-545-6684.
3. Japanese knotweed
A shrub-like perennial, knotweed has hollow stems and small white flowers that bloom in clusters in August and September.