August, 1997 Biological Control Potential to Manage Hardwood Weed Species: Chondrostereum purpureum S. F. Shamoun Strategic Importance brushing is increasing while chemical control, having peaked in 1989/90, igh demand for fiber and is decreasing. An alternative to Hdiminishing, available forest chemicals is preferred due to public land is pressuring foresters to and environmental concerns. produce more fiber while protecting environmental concerns and other Potential ofChondrostereurn resource values. Many of the most productive sites also have the purpureum to Control greatest potential for competition Red Alder from unwanted vegetation. On the Pacific Coast, red alder Foresters are required to develop (Alnus rubra) is a primary invader of prescriptions (PHSPs) identifying disturbed forest areas and is capable preferred and acceptable tree of dominating a range of sites. species, free from deleterious brush Manual cutting often encourages and tree competition, within a prolific, multi-stem sprouting from specific time. Recently, many hard­ stumps or rhizomes. Manual cutting woods have been recognized as is generally economically not feasible acceptable crop trees. However, the because of alder's ability to resprout wrong distribution or density will and grow more vigorously after suppress commercially valuable cutting. Depending upon the site, conifer crop tree growth and reduce Fruiting body of the application of the commercial site productivity. Chondrostereum purpureum herbicide glyphosate, either as a paste (Carbopaste) or as a spray Vegetation control is an essential (Vision® or Roundup®), is considered part of integrated management effective for controlli ng alder plans. It is also very important to control vegetation on competition. However, restrictions on herbicide use may ski slopes, power, rail, pipeline and other rights-of-way. increase, particularly on crown lands. For example, British Columbia Hydro spends approximately $28 million annually on vegetation management of their The results of greenhouse screenings and field trials rights-of-way. Over the last decade, more than 480,000 indicate that the efficacy of Chondrostereum purpureum hectares of British Columbia's crown land have been is comparable to the commercially used glyphosate for brushed using manual cutting or girdling, and applica­ controlling target weed species. tion of chemicals. Traditional use of chemicals is being increasingly restricted. In British Columbia, manual Acollaborative research program has been initiated between Canadian Forest Service, University of Victoria (Mycologic Inc.) and B. C. Hydro to test Chondrostereum purpureum can only the effectiveness of the candidate invade through fresh wounds or cut myco herbicide, Chondrostereum Chondrostereum stumps. This limits spread and purpureum. The objective is to register purpureum is poised uncontrolled infections. The fungus this biocontrol agent for vegetation is disseminated by short-lived control on rights-of-way and to control to become North basidiospores that are unlikely to pose competing hardwood vegetation in a risk to non-target trees. In addition, conifer reforestation sites. America's first as it is applied directly to specific hosts, it is not transported to adjacent Characteristics of a biological control species or to ground water. Mycoherbicide agent for use in Chondrostereum purpureum exists in­ Mycoherbicides are formulations of integrated forest all of North America's ecosystems. Its plant pathogenic fungi that are natural occurrence precludes the risks applied directly to target weeds to vegetation manage­ associated with the introduction of a repress or eliminate growth. The foreign species. causal agent of the disease is cultured ment strategies. on artificial media, identified and then To understand the population structure, re-inoculated on the weed host. the variation of ribosomal DNA (rONA) Apreferred mycoherbicide would: in isolates from Europe, New Zealand, Canada and the U.S.A. was • be a local or native tested. The rONA genes of pathogen; basidiomycetes constitute a • not persist at greater than multigene family making it endemic levels; ideal for population studies. • be subject to natural Initial results suggest no controls; barriers to gene flow across • have a potent North America and therefore virulence; and a relatively low risk of mov­ be applied in a cost ing an isolate from one efficient and environmen­ region to another. tally safe manner. Chondrostereum purpureum hondrostereum is a wound plant pathogen Right of way: Chondrostereum purpureum offers and has not been shown to purpureum as a viable alternative to chemical herbicides affect animal hosts. Mycoherbicide Toxicology laboratory tests Chondrostereum purpureum is a primary invader of wounds. The fungus causes sapwood stain, decay and eventually host death. However, upon weakening the host, it is quickly replaced by other, more aggressive saprobic fungi such as Coriolus versiclor, Schizophyllum commune and other microorganisms. These fungi may complete target weed mortality. This rapid succession of fungi ensures that Chondrostereum purpureum will not persist at high levels following local inundations. Environmental Considerations An extensive study in 1993 and 1994 of the natural occur­ rence in relation to its use as a biocontrol agent found that the added fructification of Chondrostereum purpureum Competing hardwoods require was the same or less than naturally occurring levels. vegetation management. 2 Application The treatment intent is to manage species and productivity for specific objectives, not to eradicate a weed species. Treatments must be considered as only one tool availabLe for silvicultural prescriptions. The formulation Chondrostereum purpureum, patented by the Canadian Forest Service, prevents desiccation of the myceLium until infection is established. Progress has been made to combine the cutting with the formulation applica­ tion. The first full-scale fieLd trial was established with the cooperation of B.C. Hydro in 1994. Chondrostereum purpureum restricts resprouting from red alder stumps Chondrostereum purpureum is cuLtured for appLication on single, dominate hardwood species. It will be applied to fresh stumps as a mycelial suspension in a paste formula­ are ongoing to ensure that human tion. Summer and autumn application can prevent wound health risks are assessed and a heaLing and thus hasten mortality. thorough taxonomic description is made available. Research is showing The best treatments can achieve up to 80% mortality. The slow mortality may Mass Production that Chondrostereum have the advantages of: Quality control is vital in the mass prop­ purpureum offers a • reducing invasion by other competin~J agation of any biocontrol agent. Two weed species; major considerations must be tested and viable alternative to • allowing other species to regenerate; controlled: stability and efficacy. chemical herbicides. • providing less shock to crop trees; and • providing less exposure to sunscald. Stability Continuing Research An important consideration in the production of a biocontrol agent is Genetic markers wilL enable "DNA the possible introduction of patho­ fingerprinting" of lead isolates and genic alleLes from the virulent strain allow researchers to folLow the envi­ selected for biocontrol into the local ronmental fate of reLeased isolates. population. Research is being done on advanced markers to ensure that the Environmental persistence and risk agent is stable during transportation. analysis is an on-going task in many regions of Canada. Efficacy Conclusion Field and greenhouse tests on the efficacy of isolates are on-going. There is a strong potential for the Experimental field trials are being formulation of the phytopathogenic established to obtain the most fungus, Chondrostereum purpureum, efficient, local isolates. to be used operationally as a biological controL agent for hardwood weed species in conifer reforestation sites and rights-of-way. Chondrostereum purpureum is applied to fresh stumps 3 Additional Reading Contacts: Dr. Simon Francis Shamoun D'Anjou, B. 1991. Manual Cutting Techniques for red Research Plant Pathologist &Coordinator, alder control in a Grand fir plantation. FRDA Research Development of Microbial Control Agents Program Memo 195. Canadian Forest Service Pest Management Methods Network DeJong, M., Sela, E. Shamoun, 5., Wall, R. 1996. Natural Pacific Forestry Center occurrence of Chondrostereum purpureum in relation to 506 West Burnside Rd. its use as a biological control agent in Canadian forests. Victoria, B.C. V8Z 1M5 Biological Control (6):347-352. 250-363-00766, fax 250-363-0775 email: [email protected] Hintz, W., Shamoun, S. 1996. Environmental fate and risk assessment of a novel forest-weed biocontrol agent. Proceedings of the 8th Symposium on Environmental Acknowledgments Releases of Biotechnology Products. • MycoLogic, a private Canadian company jointly owned by Dr. W. Hintz and the Innovation Ramsfield, T.D., et al. 1996. Geographic variation of Development Corporation (wholly owned by the Chondrostereum purpureum detected by polymorphisms in University of Victoria, B.C.). the ribosomal DNA. Can. J. Bot. 74: 1919-1929. • Canadian Forest Service - Patent for formulation. Shamoun, 5., Wall, R. 1992. Chondrostereum purpureum, a potential mycoherbicide for red alder in British • B.C. Ministry of Forests Columbia forests. Phytopathology (82): 1154 (Abstract). • Gwen Shrimpon, B.C. Hydro, Vancouver, B.C. Shamoun,