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The restructured Montana Noxious Weed
List has been
developed so that management objectives will more closely align with
the invasion
stage of each species. The documented
history of plant invasions recognizes four major stages in the
geographic
spread of weeds (Figure 1). The
“exclusion stage” is the first stage, and it occurs when introduction
of a weed
to a new area can be prevented. The
management goals of this stage are prevention, education, and awareness. This stage is the most cost-effective stage
in which to manage weeds, and therefore species in this stage often
receive
priority.
After a weed becomes established, there
is typically a lag
phase before the weed begins to rapidly increase its range. During this phase eradication is the most
effective
management strategy; populations may occur in isolated areas throughout
the
state and are still small. Aggressive
and persistent efforts may eliminate the weed or at least contain or
reduce the
population.
The third stage of invasion is the
“suppression stage.” Populations may be
expanding rapidly during
this stage. Emphasis is placed on
suppressing
infestations from further growth, especially through control of
satellite
infestations, which are small infestations that occur beyond the
existing perimeter
of a core infestation. Populations
may
be abundant and widespread in many counties, therefore integrated
management
that delivers cost-effective, long-term suppression of weeds is
critical during
this stage.
The final stage of invasion occurs when
the geographic
breadth of the invasion reaches its maximum.
Most suitable habitat has already been invaded, and
further expansion of
the weed may not occur. Effective
control is unlikely without massive resource inputs.
Often management is directed towards the use
of biocontrol and other low input methods that will suppress weed
abundance.
Priority 1A weeds in the restructured
Montana Noxious Weed
List correspond to the “exclusion stage” of the invasion process. The “eradication stage” corresponds to
Priority 1B to 2A in the restructured Montana Noxious Weed List,
depending on the
weed species and area in Montana. The “suppression stage” corresponds to
Priority 2A to 2B weeds in the restructured Montana Noxious Weed List,
again
depending on the species and area in Montana. Management
of Priority 1A species (i.e.
yellow starthistle) and Priority 1B species shall be a priority across
the
state. Management of 2A and 2B species
shall be prioritized by local weed districts because the status of each
weed in
its invasion stage will vary from county to county.
Priority 3 was created to accommodate
species that are known
to be invasive in Montana or in
nearby states,
but statewide mandated control of existing populations would cause
undue harm
to many Montana
citizens. Management criteria include
limiting the intentional sale of these species and implementation of
research,
education, prevention, and control programs where appropriate.
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