The most difficult site to tackle in plowed-ground prairie restoration is the old field. It is usually full of perennial and annual weed seed (Packard).

What is a weed?

Exotics are plants not native to Illinois. They are often called weeds; however, a weed just means that it is an undesirable plant, although it may also be native to Illinois. Exotics pose a large risk to the prairie, especially a young or severely degraded prairie, because they compete with the more desirable prairie plants for water, sunlight, and nutrients. Some examples of aggressive exotics to a to an Illinois prairie include leafy spurge, purple loosestrife, and garlic mustard. An annual ground cover like rye may be used during prairie establishment to reduce unwanted exotics. Many weedy species are annuals and can be removed through a couple of prescribed burns or manual removal. Some weeds are much more difficult to remove and can be removed with selective use of herbicides. 

Although the "weed" species will dominate a young prairie site for the first few years, they should give way to the native plant species because the native plants have genetically adapted to growing in a prairie environment.

The native prairie plants develop extensive root structure the first few seasons and eventually will outgrow the alien species. Also because of their underground development, each season's new growth is really not due in large part to plants starting from seed, but from new shoots from the underground association of roots, tubers and rhizomes. This complex association of underground growth is what prevented the early settlers from actually using the prairie to grow their crops. They found it easier to clear forested areas to start their farms. With the invention of the steel plow and its ability to cut through dense network of roots, the rich prairie soil was opened to agricultural exploitation (NRCEL). 

Weed Seed

Soil acts as a seed storage reservoir and a growth medium for weedy plants. The number of weed seed in the soil is variable and may range from 2 seeds per pound of surface soil in grassland to 140 seeds per pound of surface soil in cropland. On a per acre basis, the seed content can approach 200 million seeds per acre. A single redroot pigweed or common lambsquarter growing without competition can produce approximately 70,000 seeds (Wilson). 

Sources of Weed Seed

Seed is introduced into the soil mostly from weed seed that was allowed to mature. Weed seed can also enter a field from outside sources such as wind, water, animals, and man. Wind easily blows mature seeds easily from nearby plants. Surface irrigation water and rain runoff carries many kinds of weed seed. Many weed seeds pass through the digestive tract of animals such as birds and rodents and remain viable. 

UIS Prairie Weeds 

We have had serious weed problems with our site from the very beginning. Exotics such as lambsquarter, horseweed, and giant ragweed have been very aggressive. Several aggressive native plants, such as fleabane, hairy aster, and goldenrod, have also presented a serious challenge to the quality of the prairie. Although we have conducted numerous burns, the weed problem has been the greatest challenge. One possible reason could be attributed to many tall woody weeds that do not burn completely. Other weed control activities that we performed include mowing, sickling, and spraying herbicide (Roundup). Below is a list of the most prominent weeds on our site. Each weed includes a link to a corresponding image.

Many of the following weed images were borrowed from the

  Weed Science Society of America

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