114 Fusicoccum arbuti appears to be a wound-invading pathogen on woody tissue because 100% of wound inoculations on all trees developed cankers, whereas only 3% of surface inocula- tions did. No cankers developed from bark surface inoculations in the Arbotect, BioSerum™, Cambistat, and Tebuject treat- ments. Perhaps defenses in the bark were stimulated, preventing fungal colonization. The benzimidazole fungicides, with the exception of Arbo- tect, performed less well in the field than in vitro. BioSerum™ (phosphorous acid) was the most effective fungicide in field tests. This is probably attributable to plant defenses being acti- vated and not from fungicidal activity of the chemical. BioSe- rum™ and a similar product, Aliette (Fosetyl-Al), were not in- hibitory in culture. The previous in vitro fungicide results sug- gest the effectiveness of phosphorous acid is the result of stimulating plant defenses rather than direct fungicidal activity. Treatment with phosphorous acid holds the most promise for madrones in disease prevention and in treating preexisting can- kers. Because wounding and disease cause a defense response in trees (Percival 2001; Krokene et al. 2003), induced defenses already present resulting from active cankers on the tree before treatment with BioSerum™ were increased after treatment. Phosphorous acid, the active ingredient in BioSerum™, has been demonstrated to have a stimulatory effect on host defense re- sponses to infection by Phytophthora spp. (Fenn and Coffey 1983). Arbotect performed almost as well as BioSerum™ and a similar (induced) level of phenolic defense chemicals was seen in the foliage, but decreased in the second year after treatment. Cankers on these two treatments appeared to be more callused than on other treatments. Arbotect may behave as a plant ac- tivator in addition to having fungicidal properties. Perhaps pro- duction of phenolic defense chemicals is less important than growth of callus tissue as a mode of plant defense initiated by these two chemical treatments, although increased foliar pheno- lics may prevent colonization by fungal pathogens. All of these fungicides, except for benomyl, are sterol de- methyation inhibitors and prevent formation of ergosterol in fungi. However, effectiveness of these fungicides may be the result of their behavior in the host rather than fungicidal activity. Sterol-inhibiting fungicides are known to change the balance of plant hormones and reduce transpiration rates in some crops (Lonsdale and Kotze 1993). This confers drought tolerance on the plant and possible resistance to canker fungi such as Botryo- sphaeria spp., that are pathogenic when the host is under water stress. New infections are prevented during times when stomates are closed. Implications for Arboriculture Treating Pacific madrone trees with phosphorous acid (BioSe- rum™) or Arbotect will stimulate their defenses and reduce the severity of cankers caused by F. arbuti. These treatments also will prevent some new infections through increased defense chemicals in the foliage. The treatment effect lasts at least 1 year. These treatments may be effective on diseases caused by Bot- ryosphaeria spp. in other hosts in addition to Pacific madrone. Acknowledgments. We thank Fred Ellis of Island Foresters and Debbie Hayward of Vulcan Corp. for assistance with fieldwork and chemical applications and Will Littke, Weyerhaueser Corporation, for help with laboratory work. ©2008 International Society of Arboriculture Elliott and Edmonds: Management of Madrone Canker LITERATURE CITED Afek, U., and A. Sztejnberg. 1989. Effects of Fosetyl-Al and phospho- rous acid on scoparone, a phytoalexin associated with resistance of citrus to Phytophthora citrophthora. Phytopathology 79:736–739. Anderson, R.D., R.M. Middleton, and D.I. Guest. 1989. Development of a bioassay to test the effect of phosphorous acid on black pod of cocoa. Mycological Research 93:110–112. Brown-Rytlewski, D.E., and P.S. McManus. 2000. Virulence of Botryo- sphaeria dothidea and Botryosphaeria obtusa on apple and manage- ment of stem cankers with fungicides. Plant Disease 84:1031–1037. Crist, C.R., and D.F. Schoenweiss. 1975. The influence of controlled stresses on susceptibility of European white birch stems to attack by Botryosphaeria dothidea. Phytopathology 65:369–373. Davison, A.D. 1972. Factors affecting development of madrone canker. Plant Disease Reporter 56:50–52. Elliott, M., R.L. Edmonds, and S. Mayer. 2002. Role of fungal diseases in decline of Pacific madrone. Northwest Science 76:293–303. Farr, D.F., M. Elliott, A.Y. Rossman, and R.L. Edmonds. 2005. Fusi- coccum arbuti sp. nov. causing cankers on Pacific madrone in west- ern North America with notes on Fusicoccum dimidiatum, the correct name for Nattrassia mangiferae. Mycologia 97:730–741. Fenn, M.E., and M.D. Coffey. 1983. Studies on the in vitro and in vivo antifungal activity of Fosetyl-Al and phosphorous acid. Phytopathol- ogy 74:606–611. Graham, H.D. 1992. Stabilization of the Prussian blue color in the de- termination of polyphenols. Journal of Agricultural and Food Chem- istry 40:801–805. Haugen, L., and M. Stennes. 1999. Fungicide injection to control Dutch elm disease: Understanding the options. Plant Diagnosticians Quar- terly 20:29–38. Helton, A.W., and W.J. French. 1962. Toxicity and translocation char- acteristics of six fungicidal compounds in plum and prune trees. Phytopathology 52:1050–1056. Helton, A.W., and A.E. Harvey. 1963. Absorption, toxicity and bio- assay of high-potency fungicides in Prunus domesticus. Phytopathol- ogy 53:895–898. Hunt, R.S., B. Callan, and A. Funk. 1992. Common Pests of Arbutus. Canadian Forestry Service, FPL 63, Victoria, BC, Canada. Krokene, P., H. Solheim, T. Krekling, and E. Christiansen. 2003. In- ducible anatomical defense responses in Norway spruce stems and their possible role in induced resistance. Tree Physiology 23: 191–197. Lanier, G.N. 1988. Therapy for Dutch elm disease. Journal of Arbori- culture 14:229–232. Li, H.-Y., R.-B. Cao, and Y.-T. Mu. 1995. In vitro inhibition of Bot- ryosphaeria dothidea and Lasiodiplodia theobromae, and chemical control of gummosis disease of Japanese apricot and peach trees in Zhejiang Province, China. Crop Protection (Guildford, Surrey) 14: 187–191. Lonsdale, J.H., and J.M. Kotze. 1993. Chemical control of mango blos- som diseases and the effect on fruit set and yield. Plant Disease 77:558–562. Ma, Z., D.P. Morgan, and T.J. Michailides. 2001a. Effects of water stress on Botryosphaeria blight of pistachio caused by Botryosphae- ria dothidea. Plant Disease 85:745–749. Ma, Z., D.P. Morgan, D. Felts, and T.J. Michailides. 2001b. Sensitivity of Botryosphaeria dothidea from California pistachio to tebucona- zole. Crop Protection (Guildford, Surrey) 21:829–835. Ma, Z., Y. Luo, and T.J. Michailides. 2001c. Resistance of Botryosphae- ria dothidea from pistachio to iprodione. Plant Disease 85:183–188. Percival, G.C. 2001. Induction of systemic acquired resistance in plants: Potential implications for disease management in urban forestry. Journal of Arboriculture 27:181–192. San Juan County Health and Community Services. 2000. San Juan County Watershed Action Plan. www.co.san-juan.wa.us/health/ wtrshdpln/index.html (accessed 4/2006).
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