HANNIBAL,MO -- The Missouri Department of Conservation and University of Missouri Extension are enlisting the help of tiny bugs to help control Missouri's newest noxious weed, Centaurea stoebe micranthos, or spotted knapweed.
Seedhead weevils, Larinus minutus and Larinus obtusus or "Larrys" as some researchers like to call them, are small, flying, dark brown or gray bugs with a long snout. They can spread throughout a knapweed patch in a few years.
"Knapweed infestations occur in poor soils along rock cuts and steep slopes, and the weed produces an herbicide within its roots that kills nearby plants," explained MoDOT Roadside Manager, Chris Shulse, Ph.D. He went on to say that each plant can produce over 1000 seeds that remain alive in the soil for nearly 10 years, and that seeds are easily picked up by mowers in late summer and spread to new areas. "Needless to say, this plant is one tough character to control," Shulse noted. He also explained that this noxious weed resembles the garden flower called bachelor's buttons. "Although pretty, knapweed grows in difficult to reach areas often extending beyond the roadside onto private property," he added.
MoDOT began to release "Larry" weevils on roadsides in southern Missouri in 2008 and in northeast Missouri in 2009. The "Larrys" are released in July when knapweed is in bloom so the females can lay their eggs on the flowers. After the eggs hatch, the larvae eat into the flower and seeds, effectively reducing the ability of the plant to reproduce. A single larva can eat 100% of the seeds in a flower.
Another weevil is also helping with knapweed control. "The root boring weevil, Cyphocleonus achates, or "Cy" is larger than "Larry" and doesn't fly well, but its color helps it to blend into rocky ground," Shulse explained. The "Cys" are released in August and females lay their eggs on young knapweed plants. The larvae burrow into the roots causing the plant to die within a couple of years. Documented reductions are as high as 99% after these weevils are introduced into a knapweed patch.
In addition to the 2009 release, MoDOT introduced these hungry bugs again last month. "Although it will take a few years for the weevil populations to increase enough to make a difference, our tiny partners will no doubt play an important role in suppressing knapweed," Shulse confirmed.
For more information contact MoDOT's Customer Service Center toll-free at 1-888-ASK MoDOT (275-6636) or you can also visit us online at www.modot.mo.gov/northeast. Information about spotted knapweed in Missouri, and the knapweed weevils are available online at http://extension.missouri.edu/webster/spottedknapweed/
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