The quarterly electronic newsletter of the
Southeastern Wisconsin Invasive Species Consortium
Beginning with this issue, we will routinely highlight one or more species that can be successfully treated during the season of each SEWISC e-newsletter release. More resources for controlling these and other invasive populations can be found on our website: www.sewisc.org
Common and cut-leaved Teasels (Dipsacus fullonum and D. laciniatus)
Common and cut-leaved teasels are monocarpic perennials native to Europe, introduced to North America in the 1700s. Teasel prefers to grow in open, sunny habitats and is commonly found in more disturbed areas such as roadside ditches. Teasel grows as a basal rosette the first year or two and sends up a flowering stalk thereafter. Both common and cut-leaved teasel have large taproots, making this species difficult to eradicate.
Cut-leaved teasel generally has white flowers and blooms July through September, while common teasel blooms June through October and typically displays purple flowers. The flowers of both cut-leaved and common teasel are arranged in dense oval-shaped heads. The stalks sometimes reach 6-7 feet in height. Teasel has opposite, oblong leaves, which are prickly along the midrib, and form cups that hold water where they meet the stem. Chemical control is the most efficient way to control this species. A 2% glyphosate mixture has been found to be quite effective when applied directly to the foliage and stems before flowering occurs. After teasel is in flower, cutting the plant just below the ground surface will kill it. If seed set has already begun when the plant is cut, the seed heads should be cut and bagged to prevent further spread.
Japanese Knotweed (Fallopia japonica)
Japanese knotweed is a 5-10 foot tall flowering perennial introduced to North America in the late 1800s. This invasive species can thrive in a variety of habitats, soil types, and moisture conditions with a tendency to grow in wetlands and along riverbanks. The stems of Japanese knotweed are hollow, bamboo-like in nature, and typically green with reddish speckles. Japanese knotweed typically spreads by extensive networks of underground rhizomes, which can reach up to 6 feet in depth and 60 feet in length. The blooming period for the cream-colored clusters of tiny flowers is typically June through August. Japanese knotweed should be cut after spring leaf out and a mixture of 5% glyphosate applied on re-sprouts April through August. It is very difficult to control and a single treatment is seldom, if ever, effective so plan on making repeated applications.