What Spotted knapweed does to the habitat

Not only does Spotted knapweed out compete native plants, it engages in chemical warfare. The plants exude a poisonous chemical (catechin) that cause the roots of native plants to die.

The Spotted knapweed decreases forage for livestock and wildlife as it is not itself eaten. Since it has a taproot, it holds the soil less well and creates soil very susceptible to erosion.

Management

Here is another case where it is handy to have a flock of goats or sheep to graze away this pest.

A number of insects have been released in the western U.S. as biological control agents.

Old fashioned mowing works if you get them just after flowering but before the seeds can set. And, of course, there are herbicides like 2,4-D that will kill the plant but not effect seeds in the soil that last 5-8 years.

If it is a small patch and you elect to pull them by hand, be sure to wear gloves because the plants can cause skin irritation.

DESCRIPTION

Botanical Glossary

Centaurea biebersteineii is an herbaceous biennial or short-lived perennial that can grow between 30 cm and 1.5 m (1-4 ft.) in height. One to 20 branching, upright stems emerge from the basal leaves of the plant. The plant is slightly puberulent (short hairs). The alternate leaves are narrowly pinnatifid, getting smaller as they go further up the stem. The lower leaves are 10-20 cm (4-8 in.) in length and can be 3 cm (1.2 in.) wide, while the smaller upper leaves can be less than 1 cm (0.4 in.) long. The thistle-like flowers are purple, white or pink and are 1.3 cm (0.5 in.) tall. The flowers are present from June-October. The bracts have obvious veins; the lower and middle bracts are ovate. They are green to brown in color and have dark, pectinate tips that are not spiny. The seeds are oval in shape and brown to black, with attached pappus that is short and chaffy. Page References Fernald 984, Gleason & Cronquist 615, Holmgren 585, Magee & Ahles 1021, Newcomb 234, Peterson & McKenny 92,306.