Efficacy of excision, cauterization, and fungicides for management of apple anthracnose canker in maritime climate

Authors: GARTON, WHITNEY - Washington State University; Mazzola, Mark; DASGUPTA, NAIRANJANA - Washington State University; ALEXANDER, TRAVIS - Washington State University; MILES, CAROL - Washington State University

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2018
Publication Date: 12/18/2018
Citation: Garton, W., Mazzola, M., Dasgupta, N., Alexander, T.R., Miles, C.A. 2018. Efficacy of excision, cauterization, and fungicides for management of apple anthracnose canker in maritime climate. HortTechnology. 28(6):728-736. https://doi.org/10.21273/HORTTECH04148-18.
DOI: https://doi.org/10.21273/HORTTECH04148-18

Interpretive Summary: Cider apple is an emerging crop in western Washington and the Pacific Northwest region, but a major obstacle to planting new orchards and orchard productivity is the widespread occurrence of apple anthracnose canker, caused by the fungal pathogen Neofabraea malicorticis. The pathogen induces tree cankers that can kill newly planted trees, structurally weaken established trees, and is the primary factor limiting long-term orchard productivity in the region. Current management practices have failed to provide effective control of the disease and certain advocated control methods have not received critical assessment of efficacy. A diversity of currently employed and modified methods were evaluated in the field for the control of anthracnose canker over three growing seasons. The combination of application of Bordeaux mixture in concert with excision of cankers was the most effective treatment in limiting progression of disease beyond the treated area. However, none of the treatments demonstrated the capacity to limit the development of new infections or the suppression of potentially latent infections. Other commonly employed methods, such as cauterization of the cankered area, caused excessive tree damage and did not provide any level of disease control. As such, the cauterization treatment should be eliminated as a potential disease control option. Certain cider apple cultivars demonstrated sensitivity to applications of 0.5% sodium hypochlorite and copper hydroxide, and therefore should be evaluated on the specific cultivar prior to use. Based on the findings from this study it is apparent that additional management strategies, physical and chemical, need to be developed and evaluated for whole tree control of anthracnose canker.

Technical Abstract: This study examined the efficacy of canker excision (CE) followed by a subsequent application of cauterization (CAU) and/or chemical treatment to the excised area for the management of anthracnose canker (caused by Neofabraea malicorticis) on cider apple (Malus ×domestica) trees. Three sequential experiments were conducted from 2015 to 2017, with one experiment each year, in an experimental cider apple orchard in western Washington where trees were naturally infested with N. malicorticis. Treatments were applied once in December and data were collected January through March. Treatments in the 2015 experiment were CE + CAU, CE + CAU + copper hydroxide; CE + 0.5% sodium hypochlorite; Bordeaux mixture (BM) only; and CE + copper hydroxide (control). The 2016 experiment was identical to 2015 with the addition of the treatment CE + BM. The 2017 experiment was a repeat of the 2016 experiment with the addition of a CE only treatment and the removal of the CAU treatments. The size of the canker was measured pre-treatment, and the size of the treated area was measured post-treatment every 2 weeks for 13 – 15 weeks. On average, the area that was treated with CAU increased in size 28-fold, area treated with CE + 0.5% sodium hypochlorite or CE + copper hydroxide increased in size up to 4-fold, and area treated with BM only did not increase in size, all compared to pre-treatment. New cankers developed in all treatments 13–15 weeks after treatment application each year. Additionally, disease symptoms were present under the treated area 15 months after treatment application all years, and appeared to be similar across all treatments. Findings from this study indicate that of the treatments evaluated, the application of BM after CE was the most effective for limiting disease symptom progression in the treated area, although it did not limit development of new cankers. Initiation of new cankers observed in this study may have resulted from latent infections or new infections after treatment. Additional management strategies, physical and chemical, need to be tested for whole tree control of anthracnose canker.