110 Elliott and Edmonds: Management of Madrone Canker Arboriculture & Urban Forestry 2008. 34(2):110–115. Injected Treatments for Management of Madrone Canker Marianne Elliott and Robert L. Edmonds Abstract. Pacific madrone (Arbutus menziesii) has been experiencing a decline in the Puget Sound area, primarily as a result of a canker disease caused by the fungus Fusicoccum arbuti. Cultural methods such as prevention of stress and wounding are recommended to control canker diseases on trees. In addition to these, injected treatments can be used to protect valuable Pacific madrone trees in urban areas. An experiment testing injectable chemical fungicides and plant activators was performed on Pacific madrone trees inoculated with F. arbuti. There was little correlation between fungicidal activity in culture and canker reduction in the field tests. Two treatments that were effective in minimizing canker growth in inoculated madrones were Arbotect (Syngenta Crop Protection Inc., Greensboro, NC, U.S.; a triazole fungicide) and BioSerum™ (phosphorous acid). Cankers on wound inoculations were 50% smaller than the control group and no infections occurred on surface-inoculated treatments. Increased callusing was observed on cankers on trees with these treatments and the mode of action for these chemicals is probably stimulation of plant defenses rather than fungicidal action. Phosphorous acid is recommended in addition to cultural methods that improve tree vigor for high-value madrone trees in urban landscapes; however, heavily infected trees that have lost most of their crown will probably not benefit. Key Words. Arbotect; Botryosphaeria; canker; Fusicoccum; injectible fungicide; Pacific madrone (Arbutus menziesii); phos- phorous acid; plant activator. Pacific madrone (Arbutus menziesii) is a broadleaf evergreen tree whose native range extends from southern California, U.S. to coastal British Columbia, Canada and is an important land- scape tree in Seattle, Washington, U.S. city parks, streets, and homes. Pacific madrones are a drought-tolerant, low- maintenance alternative to some other popular species such as oak or maple. There is much interest in a method that will reduce the impact of diseases, like madrone canker, on some of the larger, more valuable trees. Pacific madrones have been experiencing a decline during the past 30 years (Davison 1972; Hunt et al. 1992). The decline first became obvious after a period of drought in the late 1960s in urban areas of Seattle, Washington, where there was an aging population of madrone trees. A canker disease caused by the fungus Fusicoccum arbuti (formerly known as Hendersonula toruloidea or Nattrassia mangiferae) is primarily responsible for the decline (Elliott et al. 2002; Farr et al. 2005). This fungus has a sexual stage in the genus Botryosphaeria, a group of latent, endophytic fungi in twigs and branches, and become pathogenic when the tree is under stress (Crist and Schoenweiss 1975; Ma et al. 2001a). Because Botryosphaeria can exist in a latent or asymptomatic form in healthy tissue until reduction of host de- fenses permits symptom expression, it is not always possible to detect and/or eradicate the fungus from trees. Foliar applications of systemic fungicides have been effective against Botryosphaeria infections on orchard crops (Lonsdale and Kotze 1993; Li et al. 1995; Brown-Rytlewski and McManus 2000; Ma et al. 2001b, 2001c). Symptoms were reduced in apple trees sprayed with kresoxim–methyl, benomyl, or trifloxys- trobin, but the fungus was still present in xylem tissue, suggest- ing that it was not eradicated and would produce symptoms at a later time when the host was susceptible (Brown-Rytlewski and McManus 2000). Plant activators are chemicals that are not necessarily toxic to fungi or host plants, but stimulate defense responses in plants. ©2008 International Society of Arboriculture This response is termed systemic acquired resistance (SAR) and has been well studied in crop plants but not as extensively in trees until recently. There are several mechanisms that operate in the host during a SAR response, including induction of enzymes such as chitinase, peroxidase, and lipase. Chemicals, including jasmonic acid and salicylic acid, are produced and act as mes- sengers that turn on other genes resulting in the defense response (Percival 2001). Phosphorous acid has been used with some success as a plant activator in providing systemic protection against Phytophthora diseases of trees (Fenn and Coffey 1983; Afek and Sztejnberg 1989; Anderson et al. 1989). Plants treated with Fosetyl-Al, an organophosphate chemical, have increased levels of phytoalexins (Percival 2001). Triazole fungicides also have been shown to behave as plant activators (Lonsdale and Kotze 1993). Plant activators and systemic fungicides are applied to trees by foliar spraying, soil drenches, and injection directly into the xy- lem. Spraying and soil drenches are not options in urban or forested environments when there is concern about the effects of the chemical on nontarget areas and beneficial organisms such as mycorrhizal fungi, epiphytic fungi such as Trichoderma spp., and yeasts, and so these methods are mostly used in orchards. Injection of chemicals into the xylem allows the chemical to be delivered directly to affected tissues in the case of vascular wilts and cankers. Injected treatments have been used to manage Dutch elm disease (DED) (Lanier 1988; Haugen and Stennes 1999) and Cytospora canker of Prunus (Helton and French 1962; Helton and Harvey 1963). Injecting chemicals into the root flare and using a shallow, small-diameter hole into the most recent sapwood have been shown to provide the most uniform distri- bution of the chemical and best wound closure after injection (Stipes 1988). Dosages are based on calculations involving tree diameter and are calibrated to be slightly less than the concen- tration that would be phytotoxic. The chemicals can be delivered using two injection methods: microinjection, in which a small volume of concentrated chemical is injected into the xylem un-
March 2008
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