Issue 12, July 16, 2010

Highway Invasives: Road Spread Weeds

We discussed in past articles several invasive insects that make their way from location to location with help of unsuspecting citizens. One such method includes traveling our highway and interstate system. But did you know that along these same highways and interstates lurk many invasive plants? Roadways and highways are becoming one of the major pathways by which invasive plants spread. Wind and air movement from passing vehicles help disperse seeds. Cutting and mowing, and regular road maintenance activities can aid in the spread of these invasives.

The purpose of this article is to increase awareness of invasive species in Illinois, particularly those you may notice while travelling on roads you may routinely use. There are more invasive plants than just listed here; and remember, there are many native species along Illinois roadsides as well.

Common Teasel -- Common Teasel was discussed in the previous issue of the Home, Yard and Garden Pest Newsletter. This purple flowering plant may reach 6 to 7 feet in height. While beautiful to look at, it also becomes established quickly and can exclude all native vegetation.

Common Teasel (Photo courtesy

Spotted Knapweed -- This plant has a very deep tap root that may aid in soil erosion and surface runoff. It releases toxins that prevent native plants from growing, making restoration difficult.

Spotted Knapweed (Photo courtesy

Autumn Olive -- Autumn olive can be identified by the underside of its leaves that are silvery and dotted; it produces yellow flowers and red fruits. This plant was introduced to control erosion but tends to crowd out natives plants.

Autumn Olive (Photo courtesy

Tree-of-Heaven -- Tree-of-Heaven grows rapidly and establishes in dense stands (like autumn olive). It overruns native vegetation and produces toxins that prevent native growth.

Tree-of-Heaven (Photo courtesy

Poison Hemlock -- This common invasive plant forms dense stands along roadways and in ditches. While it grows quickly and displaces native plants like the plants listed above, it also can harm people. All parts of the plant are poisonous and the plant sap can also irritate the skin, causing rashes.

Poison Hemlock (Photo courtesy

--Stephanie McLaughlin and Kelly Estes

Kelly Estes

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