| BEN |
| BOTANICAL ELECTRONIC NEWS |
|---|
| ISSN 1188-603X |
| No. 318 December 15, 2003 | aceska@victoria.tc.ca | Victoria, B.C. |
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Note: Manuscript cross-posted to both BEN (Botanical Electronic Newsletter) and IBGnews (International Bioherbicide Group news).
Introduced to Western Europe during the 19th century, Giant Hogweed, Heracleum mantegazzianum Sommier et Levier, has become a persistent invasive weed along water ways, road verges, and foot paths, both in open land and forest gaps. Most European countries are now banning or severely reducing the use of chemical pesticides in certain habitats such as water ways and nature reserves, which hampers the quick and cheap control of Giant Hogweed. At these sites, the most common practice to handle Giant Hogweed is annual mowing. However, this does not prevent the plant from regrowing and flowering. A biological way to control this plant may open new possibilities. An EU-project aiming to develop an integrated management strategy that comprises effective, practicable and sustainable means of controlling Giant Hogweed was started in 2002 (Seier, 2003). In this project, the Danish partners collect insect herbivores and pathogens of Giant Hogweed, and investigate and evaluate presently applied chemical and mechanical control methods.
In September 2003, the Danish Institute of Agricultural Sciences, the Royal Veterinary and Agricultural University, and the Danish Centre for Forest, Landscape and Planning, was visited to discuss prospects of a novel mycoherbicide based on Sclerotinia sclerotiorum (Lib.) De By. to control Giant Hogweed. During our stay in Denmark we also visited six sites that were investigated by Charlotte Nielsen for research into damaging insects and fungal pathogens. The plots differed from each other by light intensity, ground-water level and soil type. This gave an impression of the varieties in the Danish landscape, and differences in phenotypes of Giant Hogweed, as well as possible sensitivity of the host to several biotic and abiotic factors.
Only seedlings and dead flowering stems of Giant Hogweed were present during time of visit (22 September to 6 October, 2003). One plot had been surveyed two years ago on fungal pathogens of Giant Hogweed (Ernebjerg, 2002). Although at that time a severe infection by Sclerotinia sclerotiorum of Giant Hogweed was encountered, the fungus was not detected in 2003. Nonetheless Charlotte Nielsen found a few sclerotia of Sclerotinia sp. at a nearby site inside a flowering stem in late summer of 2003. Barend de Voogd found during the visit pathogenic fungi inside a stem tissue after splitting a number of stems of Giant Hogweed at the lower part. Only in one flowering stem at the 3rd visited location, he found hitherto unidentified small sclerotia. After isolation and subsequently cultivating we can state that it is probably S. sclerotiorum, and looks on PDA the same as the sclerotia found earlier by Charlotte Nielsen.
During the visit to the 4th sampling site, with half of the stand cut after flowering, we frequently found on the cut half old roots with new leaf sprouts. The non-cut half had decaying roots. Seedlings were present in the whole plot. Beside these extensive field surveys, the Dutch had many fruitful communications with their Danish colleagues about a promising new way of biological control of Giant Hogweed. The efficacy of Sclerotinia sclerotiorum to control Giant Hogweed was studied in 2002-2003 by Barend de Voogd in roadside vegetation in the municipality of Zutphen, the Netherlands, where it was established for more than five years. A new mycoherbicide, based on mycelium of S. sclerotiorum, was applied as a liquid mycelial suspension early spring 2002, before leaves were unfolded. First results appeared in August 2002, when in the treated plot only dwarf-plants developed with chlorotic yellowing leaves, after regular cutting of the flowering plants in June 2002. Untreated plants recovered after the June cutting. The subsequent year, some plants recovered, but when cut in June 2003, the great majority disappeared, and only 4 plants out of 17 inoculated plants showed some weak regrowth. Thus the great majority was killed by the bioherbicide (76%). The open spot was taken over by several herbs, indicating that treatment was not detrimental for other dicotyledonous plants. Plants in the untreated plot recovered with large leaves. Inoculation later in 2002 (May, August, October) did not result in a significant growth reduction. We think that a combination of optimal development of both Giant Hogweed and the pathogen, S. sclerotiorum, is crucial. When growth activities of the host cease in winter time and those of the pathogen are far better off, we may expect best control. An alternative explanation of effectiveness of the pathogen to control Giant Hogweed is due to its quasi-perennial character of its root system. Once entered, the pathogen is apparently capable as a sort of systemic bioherbicide to infect the root system. If the plants life cycle was strictly biannual, the root should die after flower-setting, also in the absence of a pathogen, which clearly was not the case. We observed in our experimental plot that Giant Hogweed can be considered a monocarpic perennial, which was also suggested by Tiley et al. (1996). This perennial nature may be stimulated by mowing plants before flowering and we would like to define subsequent state as "pseudo-perennial". During the visit to a sampling site in Denmark, with half of the stand cut just after flowering, we frequently found on the cut half old roots with new leaf sprouts. The noncut half had only decaying roots. Seedlings were present in the whole plot. Although these results are only from one experiment and on a small scale, they look quite promising. More research is indeed needed, but the results indicate that spread of Giant Hogweed can be limited by Sclerotinia sclerotiorum.
We thank dr. Aad J. Termorshuizen, Biological Farming Systems, Wageningen University, The Netherlands, for his help with editing, prof. dr. Ariena van Bruggen, Trudie Coenen, Oscar de Vos, dr. Anne van Diepeningen of Biological Farming Systems provided general support. Dr. Jorgen K"hl, PRI, Wageningen, the Netherlands) supplied diseased sunflowers with sclerotia of Sclerotinia sclerotiorum. Mr. Rob Visser, Public Green Zutphen, gave permission to carry out research in the municipality of Zutphen. Dr. Hans-Peter Ravn (Danish Centre for Forest, Landscape and Planning, Horsholm, Denmark), and dr. Niels Holst (Danish Institute of Agricultural Sciences, Flakkebjerg, Denmark) gave scientific advice, dr. Iben M. Thomsen (Danish Centre for Forest, Landscape and Planning, Horsholm, Denmark) gave mycological assistance. We had scientific meetings in Jutland with dr. Marian Erneberg, dr. Rita Merete Butterschon and Susie Nielsen (MSc student). Dr. Adolf Cesta (BEN) and dr. Maurizio Vurro (IBG news) gave additional advice.
Concern has been mounting in recent years over the domination Common Reed, Phragmites australis (Cav.) Trin., has established over many wetlands, particularly in eastern North America where it had previously been a stable, innocuous member of the native plant community. (See http://www.invasiveplants.net/phragmites/ for a history and other information.) Studies carried out by Cornell University and others suggest that an aggressively invasive Eurasian strain has replaced native members of the complex and have become a virtual monoculture in many previously varied wetlands.
As a means of understanding the extent of penetration of the alien strain(s) across the continent, principals of the program offered to determine whether collections submitted to them were native or non-native. Of those sent from the North Okanagan one stand was indeed identified at being non- native and this has already spawned a larger stand on the other side of Highway 97 north of Vernon and approximately 100 m from Swan Lake, showing that the invasive race is already present in the interior of British Columbia.
The Invasive Plants website above describes several points of differentiation between native and non-native strains and provides a reliable source for this information, however, the gross appearance of alien specimens north of Vernon does suggest a quick preliminary decision may be possible in some cases in that plants tend to be more robust than native and carry longer, fuller, spikes of a distinct purple colour when in flower compared with the skimpier, browner, heads of native race(s). On this basis it is presumed that a vigorous stand of purple-headed plants on Indian Reserve land at the head of Okanagan Lake, seen many years ago, is also alien and may be the source of the Highway 97 plants. Similarly, browner specimens at the north end of Osoyoos Lake in the South Okanagan and at Deadman Lake farther north have the appearance of native strains although none has been examined for the more exacting details described in the Invasive Plants website. As the alien Phragmites is able to eliminate other wetland species equally as well as Purple Loosestrife (Lythrum salicaria L.), specimens in or near all sensitive areas should be examined at this relatively early stage of spread, preferably through an official program of the Ministry of Water, Land and Air Protection.
For other articles on Phragmites australis in BEN see the following links:
The article regarding requirements for inventory in BEN # 317 is interesting, and I agree with Paul Catling and Tony Reznicek from a technical perspective, but their comments do not address all of the realities we face in consulting. The consulting industry is, unfortunately, geared to the timeframes of the planning process, rather than natural environments, and constrained by clients to the minimum tasks they need to secure development approvals. This often, precludes meeting the various minimums noted by Paul and Tony. I cannot see this changing unless it is regulated.
The Province(s) should take lead role and establish standards for inventory and impact assessment. This is a real issue. Since our company does a lot of peer review work for municipalities, we see a lot of other consultant's work and it is often less than adequate, falling well short of what I consider to be the minimum required. This is often not the fault of the consultant, but a reflection of what planners and client know they can "get away with". Developers have no standards for inventory and impact analysis they have to meet, and thus they do the minimum. Sometimes it seems that if the right title is on the report (e.g." Environmental Impact Study"), the applicant can say he fulfilled his obligations, and it is good enough to submit in support of a development application, notwithstanding the contents.
It is even argued that the appropriate content of a biophysical analysis for a development application should only include what is needed for approval (since that is the objective of the exercise from the applicant's perspective), thus the fault for inadequate inventory can be placed with the regulators. The development industry, in this case, will argue they are only doing as much as they are being told to do. I should add that I do not want to paint all developers with the same brush. There are many out there who genuinely want to do the right thing and give consultants considerable latitude to develop appropriate work plans.
Municipalities and other approval agencies do not have any legislation or even policy to fall back on that would enable them to demand better work be done. Here in Ontario, if municipalities object to shoddy work, the matter is often referred to the Ontario Municipal Board, and they generally place emphasis on the planning merits of an application and "minor" issues like completeness of inventory falls to the wayside.
Anyhow - that is my perspective, sorry for the cynicism. It is nice that Paul and Tony have articulated this complete list of requirements, but for the majority of work done by the private sector - I do not see it making a difference.
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