Teasel: A Noxious Weed Invading Roadsides in Missouri

Biology:
Both common and cutleaf teasel are biennials, with peak emergence of seedlings occurring in early fall or spring. Basal rosettes grow up to 22 inches in diameter, and populations form dense communities. This contributes to teasel crowding out native vegetation such as fescue. If seedlings emerge in the fall, plants will survive for two winters. For spring emerging seedlings, rosettes only survive one winter. Following winter, plants bolt and reach up to 2.5 meters in height.

Research objectives:

1. Understand the biology and reproductive capabilities of cutleaf teasel under Missouri conditions.
2. Identify seed viability following initial flowering.
3. Determine if the timing of mowing impacts teasel seed production.
4. Examine the use of different herbicide programs for managing teasel.

Preliminary results:
A survey of the literature suggests that teasel produces up to 3,000 seeds per plant. Our initial results reveal that plants growing in the absence of other plants produce up to 13,200 seeds, while plants in close proximity to other plants produce up to 3,800 seeds. Concerning flowering, viable seeds are first detected in as little as 12 days following flowering, which suggests that mowing plants during flowering may not be a practical method for teasel management. When plants are mowed when flowering just begins, regrowth occurs for plants, but viable seeds are not produced. It is not known if mowing plants when bolting first occurs will lead to regrowth in a sufficient time period such that viable seed are produced. There are only two registered herbicides for control of teasel, but agronomically acceptable control of teasel was determined at 60 days following treatment for: glyphosate, dicamba + diflufenzopyr, 2,4-D + triclopyr, 2,4-D + picloram, 2,4-D + clopyralid, metsulfuron-methyl, imazapyr, and sulfometuron-methyl.