Efficacy of fungicide treatments for control of anthracnose canker in young cider apple trees in Western Washington

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

Submitted to: HortTechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2019
Publication Date: 2/4/2019
Citation: Garton, W., Mazzola, M., Alexander, T.R., Miles, C.A. 2019. Efficacy of fungicide treatments for control of anthracnose canker in young cider apple trees in Western Washington. HortTechnology. 29(1):35-40. https://doi.org/10.21273/HORTTECH04201-18.
DOI: https://doi.org/10.21273/HORTTECH04201-18

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 fungicidal chemistries were evaluated in the 2016 and 2017 orchard growing season for the ability to limit expansion of anthracnose cankers and prevention of initial tree infection by the pathogen. The fungicides examined included zinc, basic copper sulfate, captan, thiophanate-methyl, and pyraclostrobin plus boscalid. None of the treatments were effective in preventing tree infection by N. malicorticis. Basic copper sulfate treatment did limit canker expansion, however depending on the product label, application of this treatment may be limited to a single application during the dormant season. Such a treatment schedule may not be sufficient to provide effective management over multiple growing seasons. developed and evaluated for whole tree control of anthracnose canker. Further studies are needed to evaluate additional systemic fungicides such as thiabendazole and pyrimethanil in order to formulate an effective anthracnose canker management program.

Technical Abstract: Anthracnose canker, caused by Neofabraea malicorticis significantly threatens the sustainability of cider apple production in the maritime Pacific Northwest. The cankers in the short-term reduce overall orchard productivity and in the long-term reduce an orchard’s economic life span. The disease is difficult to manage using cultural practices, and information on fungicide efficacy is limited and contradictory. A 2-year study was conducted to evaluate efficacy of the chemistries zinc, basic copper sulfate, captan, thiophanate-methyl, and pyraclostrobin plus boscalid to manage anthracnose canker infection on cider apple trees in the PNW. Trees used in the first year of the study were found to be infected by anthracnose canker upon receipt, so trees were sourced from outside the region for the second year. Thus, in the first year (2016) the study measured disease control, and in the second year (2017) the study measured disease prevention. None of the fungicide treatments evaluated inhibited canker expansion in 2016 when applications were made every 3 weeks from March through October, nor did they limit the development of new infections in 2017 when applications were made every 3 weeks from February through April. While the size of cankers treated with basic copper sulfate increased up to 8 months after initial application in 2016, the rate of expansion was significantly less compared to all other treatments. However, basic copper sulfate application may be limited to a single application during the dormant season, depending on the product label. In conclusion, results from this study demonstrate that the current fungicides recommended for control of anthracnose canker are not reliably effective in the orchard environment. Future studies should assess the fungicides evaluated in this study applied in rotation with additional systemic fungicides such as thiabendazole and pyrimethanil for the development of an effective anthracnose canker management program.