Biological Control

Nebraska's noxious weeds are not native to the state and, in most cases, not native to the United States. These plants have been introduced either on purpose or by accident. When this happens, the natural enemies which can attack these plant species are usually left behind in the plant's home environment. Natural enemies are most often a plant disease or insect which may attack one or several species of a plant.

Cooperators 

Since 1988, the United States Department of Agriculture (USDA), divisions of Animal and Plant Health Inspection Service (APHIS) and Plant Protection and Quarantine (PPQ), in cooperation with the Nebraska Department of Agriculture (NDA) and the Nebraska Weed Control Association (NWCA), have been releasing biological control (biocontrol) agents for certain noxious weeds in Nebraska. These natural enemies are insects which have been collected from their native environment.

Screening 

Before the prospective biocontrols can be released, they are placed in quarantine to determine if they are host specific to the plants that they are intended to control. (This means the agent will only attack the intended plant species and will not affect other plants which are valuable to our environment.) Once the quarantine process is completed, the biocontrol agents are released in the field to establish insectaries. The insectaries are monitored for insect survival and population levels. When the desirable population is reached, the biocontrol agents are ready for redistribution to new locations to develop other insectaries. 

After several insectaries have been established, small populations of agents are moved to smaller noxious weed infestations.

Future 

Currently, work is being done to pursue biocontrol agents for all of Nebraska's noxious weeds. The following are actively investigating new agents for release:

• APHIS
• NDA
• NWCA 
• PPQ
• USDA

While this approach may never completely control noxious weeds, we view biocontrol as another tool to help battle these invasive plant species.

Results 

Biological control is just one part of an effective control program. It must be used along with other methods of control such as herbicides, mechanical and competitive vegetation. It takes many years after the initial release of biocontrol agents for the population to grow large enough to cause significant damage to the target plant. Rhinocyllus conicus (thistle-head weevil) is now having a significant impact on musk thistle, 30 years after it was first released.

Lancaster County Biocontrol Releases 

There are three formal release sites in Lancaster County and informal type releases and/or spread from other counties of the thistle-head weevil. Aphthona lacertosa, a leafy spurge flea beetle was released in 1996 and 1999. Gallerucella calmariensis, a purple loosestrife beetle was released in 1998. These biocontrol agents have become established but it will take several years before that they have an impact or the sites can be harvested of insects for release to other sites. See the map of Lancaster County Biocontrol of Noxious Weeds (JPG) for the location of the release sites.