Combating Invasive Species
Spot chemical treatment for red imported
fire ants at Shaw afb, South Carolina. Early
detection and rapid response are often the
keys to successful invasive species control.
(Photo: Douglas Ripley)
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 surveys 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 and waters where potential 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. As noted previously,
preventing the discharge of foreign ballast water by military vessels in U.S. ports
will reduce the introduction of invasive aquatic species.
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.3
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.
Because musk thistle, Carduus nutans (far
right), is unpalatable to wildlife and livestock,
selective grazing leads to severe degradation
of native meadows and grasslands as
wildlife focus their foraging on native plants,
giving musk thistle a competitive advantage.
To control this pest at the Smoky Hill
ang Range, Kansas, the Air Force has resorted
to herbicide spraying with specially
equipped C-130 aircraft (right) assigned to
the 910th AirliftWing, Air Force Reserve
Command, Youngstown, Ohio. (Photos:
right, Douglas Ripley; far right, U.S. Department
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. Drawbacks to chemical treatment
include its cost and potential negative impact to the environment and to the
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, the Air Force Academy, Rocky Flats Environmental
Technology Site, Buckley AFB, all in Colorado, and F.E. Warren AFB,
Wyoming, (see http://amarillo.tamu.edu/programs/entotaes/CNWB.htm; http://amarillo.tamu.edu/programs/entotaes/Biological_Noxious_Weed_Control.pdf).
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 in an effort 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 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 as a result of competition with the Asian ladybug.
Demonstration of how the Galenrucella
beetle is used to control purple loosestrife in
the biological control program at the U.S.
Military Academy, West Point, New York.
(Photo: Douglas Ripley)
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 AFB, Washington, can attest (see
case study). Biocontrol agents are tightly controlled by the U.S. Department of
Partnerships. As a member of the National Invasive Species Council (http://www.invasivespeciesinfo.gov/council/main.shtml), the Armed Forces Pest Management
Board (http://www.afpmb.org/) 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 (see http://www.weedcenter.org/weed_mgmt_areas/wma_overview.html). 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.
Proceed to Next Section: Conclusions