Arboriculture & Urban Forestry 34(2): March 2008 Table 1. In vitro testing of fungicides and plant activators.z Fungicide Tebujecty Active ingredient Tebuconazole Fungisoly Cleary 3336 Arbotect®y Alamoy Phytony Cambistaty Rovral Bayleton NuCop Cinnamite Kaligreen Subdue Maxx Aliette M-pede Actigard Compass BioSerum™y Control Debacarb, carbendazim Carbendazim Thiabendizole Propiconazole Copper Paclobutrazole Iprodione Triadimefon Copper Cinnamaldehyde Potassium bicarbonate Mefanoxam Fosetyl-Al (organic phosphate) Potassium salts of fatty acids Acibenzolar-s-methyl Strobilurin Phosphorous acid N/A Mode of action Triazole fungicide, DMI Benzimidizole fungicide, NA Benzimidizole fungicide, NA Benzimidizole fungicide, NA Triazole derivative fungicide, DMI Inorganic fungicide, EI Fungicide and plant activator, DMI Dicarboximide fungicide, NA Triazole fungicide, DMI Inorganic fungicide, EI Broad spectrum insecticide/miticide/fungicide Inorganic fungicide Acylalanine fungicide, NA Plant activator, EI Inorganic fungicide Plant activator Fungicide, ET Plant activator N/A 111 Percent inhibition 100 100 100 100 100 100 100 75–100 75–100 75–100 75–100 <50 <50 <50 <50 <50 <50 <50 0 Chemicals used in the field tests. DMI sterol demethylation inhibitor; NA nucleic acid and protein synthesis inhibitor; ET electron transport disruptor; EI nonspecific enzyme inhibitor; N/A not applicable. zResults were based on fungal growth after 7 days at 25°C (77°F). Percent radial growth inhibition was calculated as the difference from control growth. y der pressure, and infusion, in which a large volume of dilute solution is fed into the tree through gravity and taken up in the transpiration stream. Treatments should be performed on a day when the tree is actively transpiring and after a period of heavy rainfall for best results (Stipes 1988). These methods do not eradicate the pathogenic fungus, but reduce symptom expression and inoculum density so that the tree can be healthy enough to defend itself. Injected fungicide or plant activator treatments in combination with cultural methods to improve tree vigor have the most likelihood of success. Injection treatments on DED are advised when there is no more than 5% to 10% of the crown affected by disease. In general, injection treatments are not rec- ommended for trees with severe disease symptoms (Lanier 1988). Trees of reduced vigor are less likely to recover from injuries sustained during injection. There are no reports of in- jected treatments being used to manage Botryosphaeria diseases on trees. The best treatments for madrone canker are ones that will improve overall tree vigor and include cultural methods such as sanitation, prevention of wounding, and improving soil water retention. Additional protection can be used in the form of chemical treatments, especially on high-value trees. Systemic fungicides and plant activators will give additional disease re- sistance, but are costly and can be damaging in some situations. The objective of this study was to evaluate the ability of several injected chemicals to reduce damage to Pacific madrone caused by the canker pathogen F. arbuti. METHODS In Vitro Testing of Fungicides Eighteen fungicides and plant activators were tested for efficacy against F. arbuti in culture (see Table 1 for list; mode of action is indicated). Two hundred parts per million active ingredient of each chemical was added to 2% malt extract agar. Controls were plates with 2% malt extract agar and no added chemical. Nine isolates of F. arbuti collected from the range of Pacific madrone, from southern California to Washington State, were tested using three replicates of each fungal isolate. Plates were inoculated from plugs taken from active cultures and incubated at 25°C (77°F; the optimal temperature for F. arbuti radial growth) and fungal radial growth was measured at intervals of 7 days for 1 month and expressed as millimeters per day. Field Tests of Systemic Treatments The field tests took place on Lopez Island, Washington. Forests in this region are drier than those on the mainland as a result of the influence of the Olympic Mountains and Vancouver Island situated southwest and west northwest of the San Juan Islands. These land masses create a “rain shadow” effect that produces less rainfall in the islands than the rest of northern Puget Sound. At the nearest weather station at Olga on Orcas Island, the av- erage high temperature in July is 21°C (69.8°F), and the average low in January is 2°C (35.6°F) (WRCC 2006). Winter tempera- tures are usually mild, except when cold, arctic air funnels down the Fraser River Valley from Canada and drastically lowers tem- peratures. Winds may also have a drying effect, pulling moisture from vegetation and surface water, and creating drought stress during low rainfall periods. One hundred twenty-eight Pacific madrone trees were selected for field tests of the chemical treatments. These trees were lo- cated in a forested area with Douglas fir (Pseudotsuga menziesii) canopy dominants. The madrones formed a layer under the Douglas fir and many showed signs of competition for space and light. Most of the trees were intermediate or suppressed crown classes and growing at the edge or interior of the stand. The stand was considered to be intermediate in moisture conditions be- tween dry and moist woodland. Soils are deeper on this site (San Juan County Health and Community Services 2000) than in other areas of the San Juan Islands and have a thick duff layer. Typical shrubs were salal (Gaultheria shallon), Oregon grape ©2008 International Society of Arboriculture
March 2008
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