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Global Invasive Species Team listserve digest #046
Wed, 20 Oct 1999 11:54:51 -0700 (PDT)
--CONTENTS--
1. Goats may be over-rated
2. Request for information on succulent control
3. Murdannia keisak and Hydrilla verticillata
4. Buckthorn control results
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1. Goats may be over-rated
From: Eric Lane (Eric.Lane(at)ag.state.co.us)
I feel compelled to reemphasize the cautionary note sounded by David Hodge
regarding the efficacy and proper role of goat grazing in an IPM system.
Many of you may have seen all of the popular press regarding this latest
fad in how to manage weeds. While it has undoubtedly contributed a great
deal to public awareness of noxious weeds, it has also caused some damage.
I believe both the public and professional managers have been oversold on
this technique (just as herbicide companies and biocontrol experts may
oversell their products). In a well-meant effort to find alternatives to
herbicide use (or to find "natural" ways to manage weeds), the pendulum
may have swung too far. Consequently we now have numerous private
landowners in Colorado that firmly believe that goats alone are their weed
management salvation, even without the opportunity to have a single year
pass so they can look at the resulting weed populations. Professional weed
managers in Colorado that bit the hook on goats are now seriously
reevaluating the effectiveness of goat grazing and looking for ways to
integrate this tool within the broader context of an IPM program.
As David points out, goats rarely kill hardy plants, especially
perennials, like spotted knapweed and leafy spurge. Consequently, it's
like biocontrol or any other technique: you can't rely upon one technique
to eradicate, contain, and/or manage a species. I think of goats as mobile
mowers that may be somewhat selective in what they mow. That about sums up
their capabilities. If a mechanical mower wouldn't eradicate/contain your
weed population or stop seed production, it's pretty safe to assume that
goats won't either. Evaluate your weed management objectives and then seek
out the tools that will help you accomplish these objectives.
Having said all that, I believe goats may be useful and practical for
long-term suppression of large infestations of goat-palatable species in
areas where you are less worried about off-target impacts (as suggested by
Karen Budd). As a technique it also has the added benefit of cute and
fuzzy attributes that may be useful in engaging the public on noxious weed
management, but only if presented in the context of an integrated pest
management program.
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2. Request for information on succulent control
From: Mike Kelly (mkellysd(at)aol.com)
Carpobrotus edulis, Mesembryanthemum crystallinum and M. nodiflorum can be
easily controlled -- in my experience -- with 2% Roundup sprayed on. Since
some always escapes control the first time around, a followup spraying is
necessary after the extent of the original kill is known. On beaches and
dunes in San Diego and elsewhere, we have seen a native seed bank express
itself after the iceplant dies enough to allow light, water and heat to
reach the seeds. The native plants grow right up through the dying and
dead iceplant with no harm from the Roundup. A native seed bank may not
exist in areas that were heavily disturbed before the invasion of the
iceplant.
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3. Murdannia keisak and Hydrilla verticillata
From: Judy Dunscomb (jdunscomb(at)tnc.org)
Does anyone have experience in controlling Murdannia keisak and Hydrilla
verticillata? Murdannia keisak (a near relative of Asiatic dayflower that
is happily infesting freshwater tidal marshes along the Pamunkey River in
VA) and Hydrilla verticillata, which is a mud flat colonizer and has
recently been discovered in the same river system, pose a serious threat
to several rare "mud worts."
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4. Buckthorn control results
From: Ana Ruesink (aruesink(at)tnc.org)
For the past several years we have searched for an effective control
method for invasive common buckthorn (Rhamnus cathartica) in a floodplain
forest at the Conservancy's LaPlatte River Marsh Natural Area in
Shelburne, Vermont. Most recently, we compared four methods (cutting,
cutting + herbicide, girdling, and Weed Wrench). One year after the
treatment, we examined buckthorn mortality, buckthorn seedling
germination, light availability, herb cover, and herb species richness in
each study plot as well as an untreated plot.
Manual control by cutting the shrubs just above ground level was fast (~3
minutes per stem) but not effective. All stumps re-sprouted, and new
seedlings germinated in response to higher light levels (23.0 seedlings/m2
compared to 0.3 seedlings/m2 in the untreated comparison plot).
Cutting down the shrubs and treating each cut stump with glyphosate
herbicide (0.96% active ingredient marketed as Round-Up in an
over-the-counter formulation) produced the highest buckthorn mortality
rate: 47.8%. However, shrub removal produced a substantial increase in
light availability on the forest floor, promoting germination by new
buckthorn seedlings (11.5 seedlings/m2).
Girdling the stems killed 14.3% of the treated shrubs outright.
Unfortunately, many of the remaining shrubs re-sprouted below the girdle;
others produced canopy leaves as usual. This method produced the least
soil disturbance and maintained the highest degree of canopy closure, so
there was little change in percent cover or richness of native herbaceous
species.
We also tried "leveraging our efforts" with a Weed Wrench, without
success. Although mortality of mature buckthorn shrubs was 100%, a flush
of weedy, non-native herbs such as yellow rocket (Barbarea vulgaris) and
moneywort (Lysimachia nummularia) responded the following spring.
Hard-working volunteers required 15 minutes per stem to wield the Wrench,
representing a significant labor input.
Managing for native species composition in this floodplain forest has no
perfect solution. Stem-girdling appears to be the best method, and we
began a trial this year to see if we can improve our mortality rate by
girdling stems as close to the ground as possible and by girdling them
deeply to ensure disruption of the phloem. We are also mobilizing our
volunteer troops since this method requires a large crew to harvest new
sprouts each subsequent summer.