Science > Research > Application of Biological Control to Vegetation Management in Forestry

Application of Biological Control to Vegetation Management in Forestry

Simon F. Shamoun

 Background | Materials and Methods | Results | Conclusion | References | Other Publications

Background

Competition by non-commercial vegetation (forest weeds) is a serious problem in management of conifer regeneration sites. Control of competing vegetation includes removal by mechanical and manual brushing, by chemical herbicides, and by the bioherbicide strategy. A biological control strategy in natural ecosystems entails the enhancement of naturally occurring plant pathogens which have a low likelihood of soil or water contamination and minimal risk to non-target plant species. The expected result are an increase in early conifer growth rate and a shorter rotation age of commercially valuable crop trees (Wall and Hasan 1996). Three major control strategies are being used for management of forest weeds: classical, inundative (bioherbicide/mycoherbicide) and augmentative (silvicultural manipulation).

 A program on development of biological control agents for forest weeds was established at the Canadian Forestry Service-Pacific Forestry Centre. Among the target weeds considered were Alnus rubra, Calamagrostis canadensis , Epilobium angustifolium, Gaultheria shallon, and Rubus spp., including wild raspberry (Rubus strigosus), thimbleberry (R. parviflorus), and salmonberry (R. spectabilis) (Figs. 1-4). Plant pathogens from these weeds have been isolated, identified and tested for their potential use as biological control agents.

 This presentation illustrates two case studies:

• 1) Chondrostereum purpureum as a potential biological control agent for red alder in conifer regeneration sites and utility rights-of-way; and
• 2) Fusarium avenaceum as a potential agent against invasive Rubus spp. in conifer regeneration and riparian sites.

Fig. 1. Red alder	Fig. 2. Wild raspberry

Fig. 3. Fireweed

Fig. 4. Marsh reed grass

Materials and Methods

Case study I: Chondrostereum purpureum - Alnus rubra pathosystem.

An experimental field trial was established to rate biocontrol efficacy versus mechanical and chemical control methods under utility rights-of-way on Vancouver Island, BC. Chondrostereum purpureum, an endemic wood decay fungus, was grown on nutrient base, formulated, and applied as a paste to cut alder stumps. The occurrence of alder resprouting, the no. living sprouts per stump, stump mortality, and the presence of fruiting bodies of C. purpureum was assessed for 2 growing seasons.

Case study II: Fusarium avenaceum - Rubus spp. pathosystem.

Three invasive, pioneer Rubus spp., wild raspberry, thimbleberry and salmonberry were treated with inundative application of Fusarium avenaceum, an endemic foliar and stem pathogen. Inoculum production methods, amendment of inoculum with adjuvants (nutrients, humectants, surfactants), and co-application with low doses of glyphosate have been investigated to increase fungal pathogenicity. The presence of phytotoxins produced by F. avenaceum grown in a rice medium was also investigated (Oleskevich et al. 1998).

Results

Case study I: Chondrostereum purpureum - Alnus rubra pathosystem.

Chondrostereum purpureum and herbicide treatments resulted in similar levels of stump mortality and resprouting of with >95% stump mortality recorded (Table 1). Fruiting bodies of C. purpureum were observed 18 mo post-inoculation (Table 2). Results of these tests, and similar large scale field trials conducted in research sites in Ontario (Dumas et al. 1997) and in the Netherlands (de Jong et al. 1996) indicate that C. purpureum is quite effective as a biological control agent of stump sprouting in alders and aspens (Figs. 5-6).

Table 1. Mortality and living sprout number of cut stumps of red alder treated with Chondrostereum purpureum and chemical herbicides.

Table 2. Foliar necrosis of Rubus plants resulting from inundative applications of Fusarium avenaceum inoculum, originating from infested rice cultures, and combined with an organosilicone surfactant (Silwet L-77®), means + SEM.

Case study II: Fusarium avenaceum - Rubus spp. pathosystem.

Fusarium avenaceum, grown on rice grains and combined with Silwet L-77®, induced foliar necrosis within 24-48 h on R. strigosus and R. parviflorus (Table 2). The presence of moniliformin in fungal cultures may enhance virulence (Fig. 7). 

Fig. 5. Field application of Chondrostereum purpureum on alder.	Fig. 6. Fruiting bodies of Chondrostereum purpureum.

Fig. 7a. Macroconidia of FA

Fig. 7b. Production of FA inoculum on rice grains

Fig. 8. Application of Fusarium avenaceum to thimbleberry, versus water control.

Conclusion

The biological control strategy for management of competing vegetation is poised to become an essential component of forest management practices. Endemic, plant pathogenic fungi are presently considered the most promising biological control agents. Recent advances in formulation technology, phytopathology, molecular biology and silviculture have accelerated the commercialization and production of few biological control products for forestry use (e.g. StumpOut®, BioChon®, and ECOclear™). The main concern to both regulatory authorities and to the public in general, in using fungal pathogens for control of forest weeds, is their potential threat to non-target plants. This is especially relevant to classical biological control strategy, where exotic pathogens are introduced into new ecosystems. In contrast, risk analysis of indigenous fungal pathogens used as biological control agents (e.g. C. purpureum) is extremely low (de Jong et al. 1996, Gosselin et al. 1999). Recently, research investigations based on advanced epidemiological modeling systems, molecular analyses and monitoring (e.g. PCR-DNA technology: RAPD, RFLPs, rDNA and mtDNA) studies have revealed the safe use of native fungal pathogens (de Jong et al. 1996, Ramsfield et al. 1996, Becker et al. 1999, Gosselin et al. 1999). Plant pathogens which have caused serious tree losses in the new world, such as Dutch elm disease, chestnut blight and white pine blister rust disease, were introduced accidentally in forest products and nursery stocks (Manion 1981), and not through using native plant pathogens via planned biological control programs.

References

Becker, E. et al. 1999. Biol. Contr. 15:71-80.

Gosselin, L. et al. 1999. Molec. Ecology 8: 113-122.

De Jong, MD. et al. 1996. Biol. Contr. 6:347-352.

Dumas, M.T. et al. 1997. Biol. Contr. 10:37-41.

Manion, P. 1981. Tree disease concepts. Prentice Hall Inc. publisher, N.J., 389 pp.

Oleskevich, C. et al. 1998. Can. J. Plant Pathol. 20:12-18.

Ramsfield, T. et al. 1996. Can. J. Bot. 74: 1919-1929.

Shamoun, S.F. and R.E. Wall. 1996. Europ. J. For. Pathol. 26:333-342.

Wall, R.E., and Hasan. 1996. In: P.Raychaudhuri and K. Marmorosch, eds. Forest Trees and Palms Diseases and Control, pp. 1-19.

Other publications by Simon F. Shamoun

Publications about biological control

Background | Materials and Methods | Results |Conclusion | References