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May 22, 2012

MADISON -- The unusually warm and early spring of 2012 has caused most plants to speed up their usual timetable. Trees, shrubs and herbaceous plants have been leafing out and flowering between one-and-a-half to three weeks ahead of schedule, according to phenological data compiled by state officials.

"Anyone managing weeds needs to be adapting their work plan according to how plants are growing," says Kelley Kearns, a native plant conservation specialist with the Department of Natural Resources Bureau of Endangered Resources.

Kearns says roadside mowing done just before or at the early stages of flowering can prevent most weeds from setting seeds. For many of the most aggressive roadside weeds, that optimal mowing time is now for the southern part of Wisconsin, and within the next few weeks for the central and northern regions. Some invasive plants have already begun to bloom.

leafy spurge
Leafy spurge.
WDNR Photo

Large chartreuse colored patches on roadsides are leafy spurge, a noxious weed that has extensive roots that range up to 35 feet, seeds that are explosively ejected and is a major pest in pastures and hayfields. Yellow sweet clover, though useful as forage and by bees, is a highly invasive plant in prairies.

Several other invasive plants will be flowering by late May, Kearns says, including the yellow umbrella shaped flower clusters of wild parsnip. This plant causes burns when the sap gets on exposed skin, so anyone pulling, mowing or weed whipping parsnip needs to be well covered.

Canada thistle, the noxious weed that farmers have been fighting for years, will soon show its tufts of purple flowers and is generally found in large patches.

Spotted knapweed [pdf] also has tufts of purple flowers, but is generally only 2 feet high and found in sandy or drier soils, especially in the central and northern parts of the state.

"Mowing, cutting or pulling these plants before they produce seed is critical to preventing their spread," Kearns says. "If they are mowed after seeds have begun to develop, mowing equipment is likely to spread the seeds to new areas. Most of the more persistent weeds will not be killed by mowing, and may re-flower later in the summer, especially with the extended growing season we are experiencing."

Kearns says eradicating these weeds generally requires several years and a combination of pulling, cutting, prescribed fire and/or careful application of specific herbicides at the correct time.

For more details on controlling these plants, search "invasives" on the DNR website or type in the plant's name as the key word. The University of Wisconsin also has extensive control information about most of these weeds at Weed Science publications (exit DNR).

FOR MORE INFORMATION CONTACT: Kelley Kearns - 608-266- 5066 or Paul Holtan - DNR Office of Communications 608-267-7517

Last Revised: Tuesday, May 22, 2012

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