The most cost-effective means to control invasive species is to prevent their initial arrival. The impacts of many of these species, however, are not understood until they are well established. For those species where environmental and economic impacts are known, measures need to be taken to reduce the risk of introduction, including survey for these species at ports of entry and military bases where equipment and materials are imported or returned from foreign soils. Military vessels and equipment used in foreign lands where invasive species are suspected should be thoroughly cleaned before leaving those foreign lands. If any invasive species are found at our first lines of defense (i.e. shipping ports), then immediate eradication should occur.
On military lands where invasive species are already present, management activities should include restoration actions. The removal of invasive species without restoration can lead to the reestablishment of the same or new invasive species. Furthermore, on many installations, there is a chance that invasives species can reinvade from lands outside the installation boundaries. On Avon Park Air Force Range in Florida, the highly invasive and problematic climbing ferns and tropical soda apple occur in public and private lands nearby. It is important for military natural resources managers at all installations to think beyond the fenceline and cultivate public and private partnerships to keep invasive species under control.60
Early detection/rapid response
The idea of early detection/rapid response is a two-part component: first, surveys to identify newly established invasive species, and second, an effort to eradicate newly detected infestations. There are many cases where early detection has identified newly established pests, but managers have proven less adept at following up with eradication programs. Many scientists want to study the problem more, but agencies are bogged down in red tape that prevents immediate eradication. Given the potential environmental and economic impacts, a suggested strategy of “yank it now, ask questions later” may prove most cost effective. This is particularly important for species that are known to cause harm.
Mechanical control
The use of mechanical control is often effective for dealing with small, newly established populations or as part of a large-scale restoration program. Mechanical control may simply include hand pulling or the use of large equipment. No matter what control feature is employed, follow-up monitoring is necessary to ensure eradication.
Pesticides
Many modern pesticides have been vastly improved over earlier controls, such as DDT, with its notorious residual environmental impacts. Methodologies for applying pesticides have also improved. Cut-stump treatments (i.e. painting herbicides directly onto a cut surface), wet wicking (hand applying herbicides to individual target plants), and stem injections (the use of needles to inject herbicides directly into a target plant or impacted plant) allow applicators to directly apply chemicals to the target species with little or no non-target impacts. In extreme cases, broadcast spraying of herbicides may be viewed as the only option, in which case more care and review are needed. DoD has a goal that by 2010, all pesticide applicators will be certified. Drawbacks to chemical treatment include its cost and harm to the environment and the persons to handle the poisons.
Biological controls
Biological controls are growing in use as non-chemical opponents of harmful invasive species and diseases. Biocontrols can be defined as the use of natural enemies, usually from a pest’s native lands, to reduce the impact of problematic insects, diseases, and plants. There are many examples of successful use of biocontrols in the place of chemical poisons; a tiny parasitic wasp, part of a large group of parasitoids, controls many agricultural pests and diseases, for example. The Texas Agricultural Experiment Station has collaborated with the DoD to remove noxious weeds on military lands. The weeds include leafy spurge, field bindweed, spotted knapweed, Canada thistle, and St. John’s Wort; participating installations include Fort Carson Military Post, the Air Force Academy, Rocky Flats Environmental Technology Site, Buckley Air Force Base, and F.E. Warren Air Force Base.
As with any effort to tinker with Nature, biocontrol can have unintended, negative results. One danger is that the biological control agent—parasitoid, fungus, nematode, bacterium, competing organism, growth regulator—can gobble up or infect not only its intended target but also beneficial organisms. In the 1970s, for example, biologists released the Asian ladybug to control aphids that were attacking pecan trees in the southeastern U.S. These ladybugs were successful at eradicating these aphids, but they also had appetites for other insects. The result has been a biocontrol that eats so many aphids and other native ladybugs that many of native ladybugs became threatened or extinct. Even New York’s official state insect, the nine spotted ladybug (Coccinella novemnotata), is now extinct from New York State because of competition with the Asian ladybug.
These and other examples should be viewed as cautionary tales. When biocontrols are thought to be the only solution, detailed research and extensive testing must be done. Researchers and land managers need to learn from the biocontrol failures. They need to ensure that biocontrols do not become the next wave of invasive species, potentially worse than the species they were meant to control. But if carefully evaluated before introduction, biological controls can be highly effective, as Jerry Johnson at Fairchild Air Force Base, Washington, can attest (see case study). Biocontrol agents are tightly controlled by the U.S. Department of Agriculture.
Partnerships
As a member of the National Invasive Species Council, the Armed Forces Pest Management Board works with multiple agencies to combat invasive species. Throughout the country, Cooperative Weed Management Areas (CWMAs) or similar partnerships are forming to address invasive species problems across multi-jurisdictions. These partnerships may allow the DoD, along with other federal agencies, state agencies, NGOs, and local land managers, to share resources and experiences to better manage invasive species.
Next Page: Conclusions
Author
Troy Weldy, Invasive Species Expert
The Nature Conservancy
Invasive Species Management
Impacts on military operations