Biology Reference
In-Depth Information
13.6.2 ChemicalControl
There are several herbicides that provide relatively effective control of black or
PSWs when applied postemergence (Averill et al. 2008; Lawlor 2002; Weston et al.
2005). Foliar applications are generally more difficult to apply than cut stem appli-
cations because of the intertwining growth habit of the swallow-worts and high
patch densities at maturity, but are generally more effective (Lawlor and Raynal
2002). Furthermore, Lawlor and Raynal (2002) found that foliar applications were
significantly more effective at controlling plants in shaded plots than drier, full sun
plots. In particular, the most effective chemical treatments were glyphosate (10.4 kg
ai ha
−1
) applied at an early stage of flowering and triclopyr (2.6 kg ai ha
−1
) applied at
early fruit formation, both of which resulted in a 73% reduction in cover, decreased
densities, and a loss of apical dominance (Lawlor and Raynal 2002).
Recent work has demonstrated that glyphosate applied at a much lower rate
(1.79 kg ai ha
−1
) was equally as effective (77% reduction in cover when applied in
late June) as a higher rate, and more effective overall than triclopyr alone or com-
binations of triclopyr and 2,4-D or dicamba and 2,4-D (F. Lawlor, unpublished data
in Weston et al. 2005). Similarly, Averill et al. (2008) found that triclopyr applied
at a lower rate (1.9 kg ae ha
−1
) reduced PSW stem densities by 80% 2 years after a
single June application. In any case, an adequate surfactant must be included in
postemergent foliar applications so that uptake is maximized, particularly because
of the waxy cuticle present on the leaf surfaces and stems of both swallow-wort
species (Radosevich et al. 1997).
13.6.3 BiologicalControl
To date, research on the biological control of black and PSW species with insects
has been limited (Weston et al. 2005). Since most larval stages of insects do not
thrive on foliage of the alkaloid-containing leaves of the two swallow-wort species,
effective biocontrol with insects presents a strong challenge to researchers in find-
ing an herbivorous insect for specific long-term control (Christensen 1998;
Tewksbury et al. 2002). Potential pathogens of the two swallow-wort species have
not been found, although several pathogenic organisms do infect members of the
milkweed family (Weston et al. 2005).
Recently, the USDA's Agricultural Research Service (ARS) Laboratory located
in Ithaca, NY and headed by L.R. Milbrath initiated a biocontrol program targeting
both of these invasive species. The search for potential biocontrol agents has
focused primarily in Europe and Eurasia. The criteria for the biocontrol program
specifies that the candidate organism is able to be propagated in culture, can be
successfully released and established in affected regions, and remains specific to
the swallow-worts (Milbrath and Gibson 2006). Given the lack of success from
chemical and manual tactics to date, biocontrol of the two swallow-wort species
