Biology Reference
In-Depth Information
shrunk inward through treatment. The strict protocol of detailed survey and equally
detailed recordkeeping of sites that had proven so effective with barberry eradica-
tion was implemented with
S. asiatica
. Furthermore, sites are currently released
from further surveys, i.e., deemed now free of witchweed, after only multiple con-
secutive years without detectable plants. If witchweed reappears on a land parcel
even five years after all plants had been destroyed, the parcel is reinserted into the
yearly survey scheme (APHIS/PPQ 1992, R.C. Horne, pers. comm.).
Strict application of these principles since the late 1950s has borne stellar
results: total area still occupied by
S. asiatica
as of mid-2007 had shrunk from a
maximum range of 162,000 ha (Westbrooks 1993) to a total of < 1,000 ha in the
Carolinas (Witchweed Eradication Project Status Report 2007) (Fig. 3.3). At this
rate of range reduction, witchweed may be eradicated in the next 5-10 years - a
seemingly long time on what has already been a long (49 years) and expensive
(estimated at $250 million, Eplee 2001) program. But this total cost is obviously a
small fraction of even the annual value of the US corn crop, which was valued at
$52.1 billion in 2007 (http://www.nass.usda.gov/Statistics_by_State/Michigan/
Publications/Current_News_Release/nr0817.txt). However, it is fair to point out
that eradication, while in sight, has not yet been achieved, and there is the residual
concern that witchweed has colonized as yet undetected locales outside the shrink-
ing ring of active eradication (R. Westbrooks and R.C. Horne, pers. comm.).
Eradication is an admittedly elusive goal, but the benefits can, nonetheless, be seen
even before the last invasive plant has been destroyed.
In addition to having incorporated salient components of the earlier barberry pro-
gram, the Witchweed Eradication Program is praiseworthy for its rapid decisions on
appropriate tactics and strategy - only two years after first detection of witchweed,
funds were appropriated for its eradication, not simply its control. Effective plant
destruction techniques (analogous to tactics, sensu Moody and Mack 1988) were devel-
oped from the Program's outset, even as the plant's biology was investigated, rather than
emerging through sequential investigations. Continued, methodical persistence, espe-
cially after decades of action, will be essential to the Program's eventual success.
3.5 Eradication of Kochia (
Bassia scoparia
) in Western
Australia: A Rare Product Recall
Most plant naturalizations stem from deliberate introductions (Mack and Erneberg
2002), and the simple majority of plant invasions have likely arisen from this pool
of species chosen for importation. Introduced plants have been envisioned as sources
of food, fiber, medicine, seasonings, and most commonly as indoor or landscape
ornamentals (Mack 1991). Forage species, turned naturalized or even invasive, form
another class of these immigrants (e.g.,
Agropyron cristatum, Bothriochloa ischae-
mum, Cynodon dactylon, Trifolium repens
) (Heady 1975; Gabbard and Fowler 2007
and references therein). Preintroduction assessment of these species, if indeed any
assessment was performed at all, has consistently dwelled on the species' palatability,
