Arboriculture & Urban Forestry 34(2): March 2008 Table 4. Effect of injected treatments of fungicides and plant activators on Pacific madrone canker growth.z Treatment Control Alamo Arbotect BioSerum™ Cambistat Fungisol Phyton Tebuject z 2003 124.85 (19.35) b 88.43 (13.71) ab 83.13 (12.89) ab 48.81 (7.57) a 102.83 (15.94) b 92.54 (14.34) ab 100.03 (15.50) b 90.32 (14.00) ab 2004 192.42 (29.83) c 113.97 (17.67) abc 93.61 (14.51) ab 62.72 (9.72) a 165.69 (25.68) bc 177.77 (27.55) bc 117.21 (18.17) abc 115.76 (17.94) abc Mean area of inoculated canker in centimeters squared (inches squared) is given for each treatment during a 2-year period measured in 2003 and 2004. Treatments with the same letter in year column are not significantly different at P 0.05 (Dunnett’s T3 test). which surface inoculations developed into cankers were Alamo (7%), Fungisol (13%), Phyton (21%), and control (17%). Although the differences were not significant, concentrations of phenolic defense chemicals were higher in trees treated with phosphorous acid, whereas the chemical itself was ineffective as a fungicide when tested in culture. The fungicide treatment groups were not significantly different when further samples were collected on the same age foliage in 2004 (1 year after treatment). Levels of foliar phenolics were highest in the Arbo- tect and BioSerum™ treatments, but these decreased after 1 year (Table 5). Values for other treatments increased after 1 year in the same foliage. In new foliage 1 year after treatment, the difference between groups was significant (P0.011, Kruskal- Wallis test) with the control and Cambistat treatments having the lowest amount of foliar phenolics and Phyton the highest. No relationship was found between tree dbh and canker area for individual treatments for both years. A similar result was obtained for the relationship between total foliage and canker area, except in the Arbotect treatment, in which trees with more foliage had smaller cankers (r20.55, P0.04 for 2003, r2 0.64, P 0.02 for 2004). There was more of a difference in canker size between treatments 1 year after treatment, and treat- ment effects seemed more important than the initial health of the tree. DISCUSSION In Vitro Testing of Fungicides Because chemical fungicides have not been used with F. arbuti, the concentration of 200 ppm active ingredient was chosen based Table 5. Concentrations of total phenolic chemicals (milligrams per gram dry weight) in madrone foliage for each injected fungicide treatment.z Treatment Control Alamo Arbotect BioSerum™ Cambistat Fungisol Phyton Tebuject z 2003 50.4 34.4 58.4 59.4 52.9 51.6 58.3 48.8 2004, old foliage 58.9 61.7 41.1 54.3 40.3 52.1 58.6 58.6 2004, new foliage 36.9 51.3 54.8 43.8 39.2 51.3 61.4 42.2 Samples were taken 9 (2003) and 18 (2004) months after treatment with injected fungicides. Old foliage is current year’s leaves; new foliage is newly emerging foliage. 113 on in vitro screening of fungicides for use against Botrytis cine- rea, in which the 200 ppm dose was found to be suitable for separating effective and ineffective fungicides (W. Littke, pers. comm.). Triazoles and benzimidazoles were most effective as fungicides against F. arbuti in culture. Li et al. (1995) using in vitro testing of fungicides against Botryosphaeria dothidea (Fu- sicoccum aesculi) found the most suppression of mycelial growth in plates containing carbendazim and thiophanate– methyl at concentrations of 50 and 100 ppm. These concentra- tions were lower than the 200 ppm active ingredient concentra- tion used in this study. Fosetyl-Al and phosphorous acid were both inhibitory to Phytophthora spp. in culture (Fenn and Coffey 1983) at concentrations ranging from 69 to 552 ppm, but we found they were not inhibitory to F. arbuti at 200 ppm. Fenn and Coffey (1983) report that these chemicals had low activity against a range of non-Oomycete pathogens so this result is not surprising. Copper was more effective in inhibiting fungal growth than potassium, but after a period of time in culture, the fungus was observed to accumulate copper from the medium and isolate it. After that, the mycelium was able to grow unchecked. The mela- nized hyphae of Fusicoccum protected the mycelium from lysis by potassium salts. These fungicides are commonly used to con- trol powdery mildews (Yildirim et al. 2002) whose hyphae may be more easily disrupted. The response to cinnamaldehyde was extremely variable, perhaps as a result of the volatility of the chemical. There was variability in tolerance to some fungicides among the nine isolates of F. arbuti tested. All were completely inhib- ited by 200 ppm of the triazole fungicides tebuconazole (Tebu- ject) and propiconazole (Alamo). In a study of sensitivity of B. dothidea to tebuconazole, Ma et al. (2001b) found that sensitiv- ity to tebuconazole correlated significantly with sensitivity to propiconazole. Fungicide concentrations ranged from 0.0625 to 1.0 ppm, much lower than the 200 ppm used in this study. Ma et al. (2001c) found that some isolates of B. dothidea developed resistance to iprodione (Rovral) in vitro and remained resistant when treated with up to 500 ppm of the fungicide. There was a range of tolerance to this chemical among isolates of F. arbuti at 200 ppm, but the differences were not statistically significant. Triazole and benzimidazole fungicides were the most effec- tive against F. arbuti in vitro and we anticipated that this would translate to reduction of fungal growth in established infections. Inhibition of radial growth by chemicals with fungicidal activity can be an estimator of fungicidal activity in infected host canker tissue, and this was confirmed by some of the field results. However, not all the fungicides that performed well in culture did so in the field and vice versa. How well these chemicals behave in prevention of new infections was not tested in this study and should be done by measuring inhibition of spore ger- mination. Field Tests of Systemic Treatments Because we did not want to introduce new genotypes of F. arbuti to the field site, we chose a local isolate of F. arbuti to be used in the field tests. There were no significant differences in sen- sitivity of isolates from the Puget Sound area to fungicides used in the field tests in vitro, so this isolate could be considered representative of the region. However, a more complete test should include isolates of F. arbuti from the entire range of Pacific madrone to fully account for genetic variability. ©2008 International Society of Arboriculture
March 2008
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
