Field Surveys

Aiming to close this apparent knowledge gap regarding the fungal pathogen complex associated with giant hogweed, as well as to identify potential candidates for biological control of this invasive plant, field surveys were conducted in its native range, the Western Caucasus region, as well as in its introduced European range.

In order to compile a complete inventory of the mycobiota associated with a specific plant host, as well as to assess the impact of individual fungal pathogens on that host, as wide an area as possible of its known geographical distribution needs to be surveyed. Furthermore, surveys should be conducted at different times of the growing season over a number of years to account for climatic factors affecting the distribution, incidence and severity of fungal infections and, thus, the fungal species composition (or mycobiota). An initial selection of fungal pathogens for further evaluation as potential biological control agents can then be based on field observations of the impact on the host, as well as on a preliminary assessment of the apparent host range, i.e. the presence or absence of specific pathogens in the field on plant species related to the host species in question (see also Cock and Seier, Chapter 16, this volume).

Five surveys were undertaken from 2002 to 2004 (jointly with some of the entomology surveys; see Hansen et al., Chapter 11, this volume) to assess the mycobiota of H. mantegazzianum and related species in their native western range of the North Caucasus region (Cis-Caucasus) within the Russian Federation. The geographic area covered stretched from Pyatigorsk in the east to the Krasnodar Territory and the Black Sea in the west (Fig. 12.1), and included field sites situated at altitudes between 120 and 1770 m a.s.l. On average 11 sites were visited during each survey. Population sizes of H. mantegazzianum varied from a few plants to larger stands and a representative number of diseased plant samples were taken at each site. Due to the short growing season when mountainous habitats are snow-free, these surveys were undertaken between late May and late August. The Georgian region of Abkhazia, though part of the native range of giant hogweed and of particular

Fig. 12.1. Areas surveyed in North Caucasus and Transcaucasia region during 2002-2004. Map courtesy of the University of Texas Libraries, The University of Texas at Austin (http://www.lib.utexas.edu/maps, accessed 1 June 2006); maps of Russia and the former Soviet Republics: Georgia maps, Georgia (shaded relief) 1999.

Fig. 12.1. Areas surveyed in North Caucasus and Transcaucasia region during 2002-2004. Map courtesy of the University of Texas Libraries, The University of Texas at Austin (http://www.lib.utexas.edu/maps, accessed 1 June 2006); maps of Russia and the former Soviet Republics: Georgia maps, Georgia (shaded relief) 1999.

interest due to the reported occurrence of the rust Puccinia heraclei (Nakhutrishvili, 1986), could not be included in the surveys due to political and security reasons.

While H. mantegazzianum is not native to Armenia, an additional pathogen survey was undertaken in this southern region of the Caucasus (Transcaucasia) during July 2003 to elucidate the pathogen complex associated with other Heracleum species. Of particular interest was the closely related H. sosnowskyi Manden, which has achieved invasive status in some eastern European countries such as Latvia. This survey covered the area from Yerevan to Stepanavan in the north down to Goris in the south of Armenia (Fig. 12.1), visiting in total 11 field sites situated between 1315 and 2170 m a.s.l. Representative numbers of diseased plant samples were taken according to the variable plant population sizes found at individual sites.

Table 12.2 gives a summary inventory of fungal pathogens found to be associated with H. mantegazzianum and related species in their native range together with notes on their observed distribution and impact on the host. Where applicable an initial, field-based assessment of the biocontrol potential of pathogens was made based on these data. During the growing seasons of 2002-2004, several field surveys were undertaken in the introduced range of H. mantegazzianum, particularly in the Czech Republic, Denmark, Germany, Latvia, Switzerland and the UK. The purpose of these surveys was to assess the range and type of fungal species associated with the invasive plant and to compare these with the mycobiota in the native range. In the respective countries, giant hogweed infestations were surveyed as well as natural stands of native related species, in particular H. sphondylium. In Latvia, pathogen collections were made from H. sosnowskyi, which constitutes the dominant invasive Heracleum species in all the Baltic States, having been introduced as a fodder plant during former Soviet Union times (see Moravcova et al., Chapter 10, and Ravn et al., Chapter 17, this volume).

Areas surveyed were: the western part of the Czech Republic (mainly the Slavkovsly les region; for details see Perglova et al., Chapter 4, this volume); Jutland (east and west coast) and Zealand (east coast) in Denmark; county of Hessen in Germany; Cesis and Jelgava districts in Latvia; Bern area in Switzerland; in the UK, the southern English counties of Berkshire, Cornwall, Devon, Herefordshire, Hertfordshire and Surrey, as well as Wales. Pathogens were, in general, only identified to the genus level. Fungal pathogens found to be associated with H. mantegazzianum, H. sosnowskyi and H. sphondylium during these surveys are listed in Table 12.3.

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