home - common name index - scientific name index - picture key - weedy grasses - ornamental grasses - database

List of Weedy Species – Rogue's Gallery

Frequently Asked Questions

Why should we worry about weeds and invasive species?
Where do weeds and invasive species come from?
How do we control weeds in agricultural fields?
How are weeds in gardens controlled?
What about weeds in lawns?

Why should we worry about weeds and invasive species?

Weedy and invasive species can have a tremendous impact on an area, both ecologically and economically. Invasive species may out-compete native species, impacting the vegetative structure of the community and the wildlife that depend on it. According to Pimentel et al. (2000), an estimated 500 non-native plant species have become weed pests in agriculture. Together, all weed species in crop systems in the United States cause a reduction in yield of approximately 12%, resulting in a loss of $33 billion annually. Non-native species may persist in a region for some time before becoming invasive due to a change in agricultural practices, development of competitive ability, or some other factor. An example of a species that probably existed in the U.S. for some time before experiencing a large expansion in range is the Asian lady beetle (Harmonia axyridis). This species should be familiar to most Iowans since it is now found in homes across Iowa in the winter.

Where do weeds and invasive species come from?

Many weeds and invasive species were accidentally introduced to an area. For example, it is believed that the nodding foxtail (Setaria faberi) was introduced to this country from China in the seed of Chinese millet. This weed species was first observed in New York in 1925 and now is found throughout the United States, particularly in crop fields. Other species, such as kudzu (the legume Pueraria lobata), crimson fountaingrass (Pennisetum setaceum), and Johnsongrass (Sorghum halepense) were introduced as cultivated species and have escaped. Kudzu is a distinct pest in the Chesapeake Bay region and other parts of the southeastern U.S., crimson fountaingrass is spreading rapidly throughout Hawaii, and Johnsongrass is an agricultural weed throughout the Midwest and South.

How do we control weeds in agricultural fields?

While the application of herbicides is commonplace to control weeds, it is not the only way to regulate weeds. Mechanical weed control is accomplished by the tilling of fields at appropriate times. Cultural weed control is accomplished by manipulating the cropping system to reduce the competitiveness of weeds. Cultural and mechanical weed control measures are important because they reduce the amount of herbicides necessary and because some weeds have developed resistance to certain herbicides. The fewer the herbicide applications necessary, the less likely herbicide-resistant weeds are to develop. Iowa State Weed Science is a good website to look at for information about agricultural weeds.

How are weeds in gardens controlled?

The primary methods of weed control in gardens are cultural (e.g. site preparation), mechanical (e.g. hoeing), and mulching (e.g. using natural or synthetic materials to block light from areas not planted). Herbicides are also used, but should be a method of last resort. A good place to go for information is the Iowa State University Extension Service garden publications list.

What about weeds in lawns?

Weeds in lawns are encouraged by cultural practices such as short mowing and using too much fertilizer. The Iowa State University Extension Service has publications about lawns on their garden publications page.

home - common name index - scientific name index - database - picture key - weedy grasses - ornamental grasses - Ada Hayden Herbarium - ISU

contact: