Blue Weed (aka Blue Devil, Blue-Thistle, Viper’s Bugloss) is a tap rooted invader that has been growing in communities and along the transportation routes of the East Kootenay region for decades.
Its blue flowers are definitely attractive, but the needle-like hairs on its branching stems carry a skin irritant and may be poisonous, according to the Alberta Ministry of Agriculture, so wear heavy leather gloves when handling Blue Weed.
Livestock and wildlife avoid eating this noxious weed, so there are no natural controls to prevent its spreading.
In its first season, Blue Weed seeds grow a rosette that has a many armed starfish shape. This is a good time to dig up the plant and its tap root. Blue Weed is a short lived plant, so preventing it from going to seed is an effective method of control.
When dealing with spiny mature Blue Weed, I cut it into pieces with pruning shears and use the shears to pick up the pieces and garbage can them. When the can is full, I dump the Blue Weed pieces into a garbage bag and send the bag to the dump for deep burial. If I don’t get all of the tap root out of the ground, a small squirt of Roundup into the root hole usually finishes the job.
If you take the time to remove most of the plant before using herbicide then a little dab’ll do ya.
Best management practices for any weed (except for Field Bindweed where almost all of the plant is underground) cutting and bagging most of the plant before applying a small amount of herbicide to the tiny remainder of the root is the responsible thing to do. Doing so minimizes the danger to neighbouring plants and animals.
Weed Warrior Frank