112 Table 2. Characteristics of Pacific madrone trees used in the fungicide injection study (n = 128). Mean Diameter (cm) Percent dieback Percent crown (including dead branches) 66.1 Percent live foliage 40.5 Range 14.4 (5.8 in) 70–2.5 (28–1 in) 40.2 99.0–9.0 100–30 90.3–0.5 (Mahonia nervosa), ocean spray (Holodiscus discolor), and little wild rose (Rosa gymnocarpa). Many of the trees in the stand were infected with F. arbuti in varying degrees of severity. Lopez Island is in an area severely affected by Pacific madrone decline (USFS 2003) and cankers on some trees were at least 15 years old as estimated by the number of callus layers. These trees on Lopez Island were good candidates for treatment because Fusicoccum is more aggressive on stressed trees and any treatment that was successful on them could have a good possibility of being effective on urban trees taking into account environmental factors that may influence disease development. Each tree was evaluated and data were collected on diameter at breast height (dbh) and percent dieback, crown, and live fo- liage (Table 2) and randomly placed into one of eight treatment groups with 16 trees per group. The chemical treatments selected for the field tests were Alamo, Arbotect, BioSerum™, Cambi- stat, Fungisol, Phyton, Tebuject, and a water control (see list in Table 1). These chemicals were selected based on their behavior in vitro and also to represent different chemical modes of action. All chemicals except BioSerum™ caused 100% inhibition of mycelial growth in vitro, but BioSerum™was selected for use in field tests because of its plant activator properties. Injection treatments were applied in Summer 2002 according to the label instructions for elm or oak. The test madrones were inoculated in September 2002 with a single isolate of F. arbuti taken from a Pacific madrone tree in Port Townsend, Washington. This isolate was chosen because it was close to the field site in geographic origin. Three wounds were made on branches of each tree and a small amount of fungal inoculum (approximately 3 mm3 [0.12 in3]) from a cul- ture growing on malt extract agar was inserted into each wound, which was then covered with tape to retain moisture. In addition, three areas were treated by placing fungal inoculum on the bark surface without wounding. Elliott and Edmonds: Management of Madrone Canker Canker size was measured in centimeters squared in the sum- mer of 2003 using the formula for area of an ellipse (Equation 1): Area = *a*b, where a and b are the major and minor axes of the ellipse. Foliar samples were taken from three trees in each treatment group and analyzed for total phenolic content to estimate the tree’s defense response. Total phenols were measured using a modified Prussian blue method (Graham 1992). Statistical Analysis Differences between treatment groups in both in vitro and field tests were determined using one-way analysis of variance in SPSS version 10.0. Levene’s homogeneity of variance test was performed and Dunnett’s T3 test for homogeneous subsets was used on groups with unequal variance (StatSoft 2004). For data that did not fit the normal distribution, the Kruskal-Wallis test was used instead of one-way analysis of variance. RESULTS In Vitro Testing of Fungicides In general, the triazole and benzimidazole fungicides were the most inhibitory to radial growth of all isolates. The results of the in vitro tests are given in Table 1. As expected, the plant activators showed little activity in cul- ture because their effect is to create a defense response in the plant host. Inorganic fungicides based on copper and potassium salts performed less well than the organic fungicides. There were statistically significant differences among isolates in some of the fungicidal treatments (Table 3). Complete growth inhibition of all isolates was seen in the Tebuject, Alamo, Fungisol, Cleary 3,336, and Phyton treatments. These chemicals were used in the field tests (except for Cleary 3,336). No inhibition of any isolate occurred in BioSerum™, Aliette, and M-pede treatments, and fungal growth was stimulated in some cases. Field Tests of Systemic Treatments All of the wound-inoculated trees developed cankers. Cankers on all of the injected treatments were smaller than the controls (Table 4), but the phosphorous acid (BioSerum™) treatment was the most effective compared with the untreated control group and canker area was reduced by more than 50% in 2003 (P 0.01) and almost 70% in 2004 (P 0.003). Only 3% of all surface inoculations developed cankers. The treatment groups in Table 3. Percent inhibition of mycelia growth of nine isolates of Fusicoccum arbuti from Washington and California in culture with 200 ppm fungicide.z Isolate 1. King Co., WA 2. King Co., WA 3. King Co., WA 4. Vashon, WA 5. Vashon, WA 6. Trinity Co., CA 7. Nevada Co., CA 8. Santa Cruz Co., CA 9. Santa Cruz Co., CA Mycelial growth was measured in millimeters per day at 25°C (77°F). Negative values indicate that the fungicide stimulated fungal growth relative to the control. Isolates with the same letter in each fungicide column are not different in percent inhibition (P 0.05, Dunnett’s T3 test). nt not tested. z ©2008 International Society of Arboriculture Actigard 44.8 ab 51.1 ab 54.8 b 27.8 a 45.9 ab 42.6 ab 50.1 ab 43.5 ab 39.4 ab Bayleton 82 c nt 100 d 78.5 bc 77.9 b 100 d 71.7 a 79.3 bc 77.6 b Compass 50.2 ab 45.7 ab 64.8 b 47.5 ab 40.2 a 50.9 ab 56.3 a 50.5 ab 31.4 a Kaligreen −5.1 ab 22.6 c 15.4 abc 18.9 bc 15.5 abc −1.4 ab 22.9 c −5.1 a 20.8 bc Nucop 78.4 ab 80.0 ab 86.9 b 75.8 ab 75.6 ab 76.7 ab 71.4 a 74.4 ab 69.7 a Subdue Maxx 3.8 ab 2.2 ab 15.1 b 8.0 ab 0.7 ab 4.3 ab 7.2 ab 0.47 ab −6.1 a
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