34795920_sSpotted knapweed was introduced to North America in the late 1800’s from Eurasia, where it is considered an invasive plant species throughout much of the west and Midwest. Spotted knapweed is a biennial or short-lived perennial (2-3 feet high) that has thistle like purple to pink flowers. Plants bloom from June to October, and flower heads usually remain on the plant. Plants regrow from buds on the root crown and can spread quickly through high seed production (producing 500- 4,000 seeds per square foot per year). This plant is also considered to be allelopathic, releasing a toxin that kills other plants within its root zone.

In this region spotted knapweed threatens a variety of natural and semi-natural habitats including prairies, oak and Pine Barrens, dunes, fields, forests, meadows, and pastures. It out competes native plant species, reduces native plant and animal biodiversity, and decreases forage production for wildlife.

This very persistent invasive requires an integrated control protocol that may require singly or in combination the use of cultural (hand pulling, mowing, burning), and herbicide (application of selective herbicides during bud growth in early June) methods. Although several biological control pests (seedhead weevils, root-boring weevils, and seedhead flies) have been used with some success, these bio controls have not been shown to be effective against C. maculosa. However in some instances biological control agents may be more effective when combined with other control methods such as herbicides, and revegetation with desirable, competitive native plants.

The professional staff of Wildlife and Wetlands Solutions is trained to evaluate each situation and determine the best management practice required to control spotted knapweed. Our staff is fully licensed and certified to apply herbicides and release/monitor bio controls.