Researchers take to air to manage noxious weed, teasel, along I-70

"Motorists may not know its name but they are likely familiar with the tall plant with eye-catching pink and purple flowers lining highways in summer," said Reid Smeda, University of Missouri weed scientist. "However, in fall and winter the plant resembles a thistle patch."

Teasel is a well-armored, noxious weed that crowds out native plants that wildlife depend on for food. Typically growing to six or seven feet in height teasel plants can prevent motorists from seeing deer about to charge across the road.

MU researchers are gathering remote sensing information to gauge the effectiveness of a teaselmanagement program on infested areas along Interstate 70. Teasel populations are increasing in Missouri, mainly along highway corridors and into pastures and abandoned fields off roadsides.

Researchers will be using a device called a spectroradiometer which measures how much radiant energy a surface reflects at different wave lengths. Measuring the wave length reflectance of teasel plants will allow researchers to identify their unique "special signature," Smeda said.

The signature can be adapted to multi-spectral images taken from an airplane, allowing researchers to generate a map of teasel-infested areas along a fourmile section of I-70 several miles west of Columbia. The spectral image of teasel can be distinguished from that of other plants, he said.

Researchers will test different management techniques on five plots. A mixture of cool and warm-season grasses will be sown in areas treated with different herbicides that affect the teasel but not the grass.

"The choice of herbicides was made to have some margin of safety for the grasses we are using," Smeda said.

After a year of treatment multi spectral photography over treated areas will enable the generation of updated maps that can be used to assess the effectiveness of herbicide application and grass establishment.

Aerial imaging of untreated areas also will let researchers study the rate of teasel spread in other areas.

Testing new teasel-management techniques is important because simply mowing the plant can actually make things worse in the long run, he noted.

"Current management programs to remove the plant have not been effective and mowing plants at the wrong time of the year can actually serve to spread seed and worsen the problem," Smeda said.

The plant's extended period of seed production means there is a narrow window of only 10 days in mid-July for mowing without promoting the production and spread of viable seeds.

Lateral branches also form seed heads but they initiate flowering only after the middle seed head has completed flowering. "By this time," Smeda said, "mature seeds are already being formed so if you mow that plant off viable seeds will have been produced."

Teasels have found roadsides are a good place to grow and reproduce, according to Reid Smeda, University of Missouri weed scientist.

On the other hand if teasel plants are mowed before flowering new growth can occur sending up additional shoots with seed heads. The plant may also shift from being a biennial that finishes its life that season to a perennial by creating a small rosette that will continue to develop through the fall and flower the following year.

Seed persistence is at least three years meaning a comprehensive control program must extend beyond one year.

"The use of vegetation for suppressing teasel growth will provide the most environmentally friendly technique for long-term management of teasel and minimize selection of herbicide-resistant plants," Smeda said.

This research may serve as a model for measuring infestation and assessing management techniques for other invasive species, he said.

Another way the teasel spreads may be beyond the reach of science. The plant's thistles are unique in their look and can be attractive in dry-flower arrangements which can serve as an inadvertent vehicle for spreading seeds.

"The plant has tricked us into believing it has a positive use," Smeda said. "I have seen them in flower shop windows."