What Exactly is a Noxious Weed?

Many people are familiar with the concept of weeds in the context of their yard or garden. Weeds are simply undesirable plant species. The same principle holds true for Hardin County's roadsides, natural areas, farm fields, etc., which are home to a diverse array of native plants. The number and variety of these native species is described by the term "biological diversity." Over the past 150 years, many non-native plants have been introduced to our region, both intentionally and accidentally. The vast majority of these plants coexist with native species, and are ecologically harmless.

Teasel

Teasel

Negative Impact / Spreading Ability


What makes a plant noxious in the context of Hardin County’s natural resources, is its negative impact on agriculture, or its ability to spread and crowd out native plants. This is why noxious weeds are distinguished from those weeds that occur in small numbers and are innocuous.

Noxious weeds are those able to reproduce in the wild, spread rapidly, which are difficult to control, or which cause the decline or loss of our native plants.

It is not completely understood why some weeds become noxious and some don’t. But because noxious weeds did not evolve locally, their populations are not held in check by natural predators or diseases, giving them a competitive edge over native plants.

Canada Thistle

Canada Thistle
Noxious weed species can proliferate and spread over large areas. Some are able to completely displace other vegetation, forming a homogeneous (single species) cover. Contrast this situation with the rich variety and diversity of a native plant community such as is seen in prairies, wetlands, or forests.

Reaching Hardin County


Noxious weeds are exotic plants that have reached Hardin County and Iowa by escaping from gardens, being transported by hay or straw, air, dirt, tires, clothing, etc. They grow aggressively, lack natural enemies, and resist management methods. These species can move quickly into bare areas which have been disturbed by construction or erosion, have poor vegetative cover, or have other soil disturbances.
Some of Iowa's noxious weeds are spread by windblown seed, birds, or other organisms. Other weeds spread though poorly timed mowing, or baling of hay to be fed to livestock or sold. And other noxious weeds spread by sending rhizomes (long underground roots) to uninfested areas. Most of Iowa's noxious weeds can be easily controlled through proper management. Use of mowing, cutting, burning, competitive seeding, cultivation, herbicide usage, etc., are some of the various techniques used to combat weeds. Several of the State of Iowa and Hardin County's worst noxious weeds are very difficult to control. A primary key to weed control is early detection and management, before that weed has spread and built up a large seed bank and energy reserve.

Japanese Knotweed

Japanese Knotweed