Biological Control Considerations

Weevil damage on water hyacinth plants. Several insect species and diseases feed only on water hyacinth reducing plant size and the amount of seeds it produces. This “integrated pest management” strategy reduces the amount and also the cost of herbicides needed to control water hyacinth.

The excessive growth of a weed in its new habitat may be due in part to the absence of natural enemies that normally limit or slow the growth, reproduction and spread of the weed in its native range. Classical biocontrol seeks to reunite an invasive plant with one or more of its coevolved natural enemies to provide selective control of the weed.

Classical biocontrol can be defined as the planned introduction and release of nonnative organisms (usually arthropods, nematodes or plant pathogens) from an invasive plant’s native range to reduce the vigor, reproductive capacity or density of the target weed in its new or introduced range.

Years of research are required by law to be sure the introduced insects or pathogens are “target specific.” It must be proven that they only feed on or attack a specific targeted plant (like the water hyacinth).

Classical biocontrol is by far the most common biological control method. It offers several advantages over other weed control methods. It is relatively inexpensive to develop and use compared to other methods and it may provide selective, long-term control of the target weed; because biocontrol agents reproduce, they usually spread on their own throughout the infested area.

Some of the strengths may also be shortcomings. For example, it may not be possible to find a biocontrol agent that effectively controls a single weed and selectively attacks only that particular weed. When potential biocontrol agents are identified, their establishment and suppression of the target weed in the introduced area are not guaranteed. Even if biocontrol agents do successfully establish in their introduced areas, control is not immediate and agents may require many years to have a major impact on target weeds. Finally, once a biocontrol agent is established, it cannot be recalled if desirable nontarget species are affected by the agent.

All of these considerations are taken into account when determining whether to include biological control as a strategy for managing aquatic plants in Florida.

Adapted from:
Biology and Control of Aquatic Plants — A Best Management Practices Handbook, Chapter 8: Introduction to Biological Control of Aquatic Weeds; pp 47-53; by James P Cuda, University of Florida; published by the Aquatic Ecosystem Restoration Foundation

A detailed introduction to Biological Control of Aquatic Weeds (PDF)

More information on integrated pest management in Florida