Biology Reference
In-Depth Information
rust across these areas today, almost 30 years after suspension of the Program, is
graphic testimony to its effectiveness (Leonard 2001). However, these results do
illustrate an often unappreciated benefit of an eradication campaign: even if eradi-
cation is not achieved, the population(s) of the target species are reduced to a
numerical range in which environmental/demographic stochasticity becomes an
on-going threat to persistence (Mack 2000). Lessons learned during this long cam-
paign are relevant today: a strictly-enforced prohibition of reentry by the target
species into the treatment area, thorough ground searching for all individuals over
multiple years, accurate recordkeeping, and public acceptance of the project's
necessity and benefits at the outset (Kempton 1921) pay enormous dividends.
3.4 Imminent Eradication: The 50-Year Campaign Against
Striga asiatica
(Witchweed)
Large-scale eradication efforts are not confined to the past: perhaps the largest on-
going eradication program is being waged against witchweed (
Striga asiatica
) in
the southeastern US Reasons for continuing a program that has been in continuous
operation since the late 1950s are readily apparent: similar to the impetus for the
European barberry campaign, witchweed is a huge threat to agriculture. Unlike
barberry, witchweed is a direct agent of damage, as all members of
Striga
are hemi-
parasitic plants that attack and usurp resources from their host plants, including
corn and sorghum (Eplee 1981).
The native range of the genus
Striga
is Eurasia and Africa. Consequently, there was
no question that the species had been introduced when it was discovered in cornfields
in North Carolina in 1956. Left untreated, this invasion would have almost certainly
spread far across the US and eventually parasitized corn and sorghum in the Great
Plains. Fortunately (and all too rarely) in two years, a federal/state program dedicated
to eradicating, not simply controlling, witchweed was launched in North Carolina and
neighboring South Carolina (Westbrooks 1993). Its initiation was none too soon: the
minute seeds of
S. asiatica
were being unwittingly spread in contaminated farm imple-
ments from field to field. Removing the invader mechanically (cf. eradication of bar-
berry) would have been infeasible. Instead an effective multipronged tactical approach
has been taken. In addition to direct herbicide treatment, witchweed's premature ger-
mination is induced through soil injections of ethylene or sowing “false hosts” (e.g.,
cotton and soybeans), i.e., plants that induce germination but are not parasitized by
witchweed. Either technique induces witchweed to germinate, and the plants are then
destroyed with herbicide (Eplee 1981; Westbrooks 1993).
Equally important with tactics has been the strategy (sensu Moody and Mack
1988) employed to eradicate
S. asiatica
. First, a strict embargo was placed on the
movement of farm equipment from counties infested with witchweed, thereby
minimizing the plant's further spread. Second, the Program wisely concentrated its
first eradication effort on the small, outlier populations (Eplee 1979). Consequently,
new populations could not readily arise while the infested area was being steadily
