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The Global Invasive Species Team | |
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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 --------------------------------------- 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. --------------------------------------- 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. --------------------------------------- 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." --------------------------------------- 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. |
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