Invasive Plants of Wisconsin
| Centaurea
biebersteinii DC (=C. maculosa auct. non Lam) spotted knapweed Family: Asteraceae |
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Spotted knapweed is a serious invader of sunny sites and is especially troublesome in Wisconsin on sandy sites of low productivity, including grasslands, barrens and great lakes dunes and beaches. It frequently invades sandy fields or pastures and can form nearly pure stands after a few years. Disturbance of the land encourages spread of spotted knapweed, but it can invade undisturbed dunes and other natural communities even in the absence of disturbance. Spotted knapweed appears to produce substances that inhibit the growth of other plants nearby (it is therefore said to be "allelopathic"). It is also unpalatable to most animals and it is not controllable by fire. Development of biological controls is underway and some success has been achieved through repeated mowing or hand cutting or pulling of plants, but it must be a dedicated, continuous program applied over several years--until the seed bank has been exhausted. Instructions for chemical control (and other methods as well) can be found at several locations on the web.As is the case for most invasive species, the best management is to monitor on a regular basis and to find and destroy new populations when they are small. Small populations can be hand pulled or the flower heads removed until the population is eliminated. People working at control of spotted knapweed are advised to wear sturdy gloves, as there is some suspicion that repeated contact with the plants can be hazardous.
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