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Parama Sikdar, Mike Willett and Mark Mazzola

Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens are fungal pathogens that cause postharvest speck rot and Sphaeropsis rot, respectively, in apple. Under quarantine regulations established by the Chinese government, export of apple from Washington State to China was banned between 2012 and 2014 because of detection of these pathogens in apple shipments. Previous studies established that pycnidia of P. washingtonensis and S. pyriputrescens survive in twig cankers on manchurian crabapple which serves as a dominant pollinizer in the Washington State apple industry. These pycnidia serve as a primary source of inoculum for infection of apple fruit in the orchard. The objective of this research was to conduct a study at multiple locations in Washington State to determine the efficacy of implementing manchurian crabapple pruning as a method to control speck rot and Sphaeropsis rot in storage. Four commercial orchards at geographically distant locations in Washington State were selected in 2014 and three in 2015. In 2014, two treatments included preharvest pruning of manchurian crabapple and postharvest application of pyrimethanil and untreated control. In 2015, preharvest pruning alone (PO) of manchurian crabapple was included in addition to the two treatments examined in 2014. Pruning conducted in concert with postharvest fungicide treatment significantly reduced the incidence of speck rot and Sphaeropsis rot in storage during the initial experimental field season. During year 2, both the PO and pruning with postharvest fungicide application controlled fruit rot with no significant difference between the two treatments. Findings from this study will be instrumental for the control of these postharvest diseases and maintenance of international market access for fruit from the Pacific Northwest.

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Whitney J. Garton, Mark Mazzola, Travis R. Alexander and Carol A. Miles

Anthracnose canker, caused by Neofabraea malicorticis, threatens the sustainability of cider apple (Malus ×domestica) production in the maritime climate of western Washington. In the short-term, the disease reduces overall orchard productivity and in the long-term it reduces an orchard’s economic life span. The disease is difficult to manage using cultural practices, and information on fungicide efficacy is limited and contradictory. To address this situation, a 2-year study was conducted to evaluate efficacy of zinc (4.49 lb/acre), basic copper sulfate (2.49 lb/acre), captan (2.94 lb/acre), thiophanate-methyl (0.69 lb/acre), pyraclostrobin plus boscalid (0.38 lb/acre), and combinations of these fungicides to manage anthracnose canker infection in young cider apple trees cultivated in a maritime climate. Trees used in the first year of the study (2016) were found to be infected by anthracnose canker on receipt, so the first year was a measure of disease control and the second year (2017) was a measure of disease prevention. In 2016, when fungicide treatments were applied every 3 weeks from March through October, none of the treatments evaluated inhibited the development of new infections or the expansion of existing cankers (77% increase in canker size on average for all treatments). In 2017, when fungicide treatments were applied every 3 weeks from February through April, two to three new cankers were observed 3 weeks after final treatment application for all treatments. Results from this study demonstrate that the current fungicides recommended for control of anthracnose canker are not reliably effective in the orchard environment of northwest Washington. Future studies should assess the fungicides evaluated in this study applied in rotation with additional systemic fungicides.

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Whitney J. Garton, Mark Mazzola, Nairanjana Dasgupta, Travis R. Alexander and Carol A. Miles

This study was designed to determine the efficacy of canker excision (CE) followed by a subsequent application of cauterization (CAU) and/or fungicide treatment to the excised area for the management of anthracnose canker (caused by Neofabraea malicorticis) on cider apple (Malus ×domestica) trees. Three 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 included the same treatments as in 2015 plus one additional treatment, CE + BM. In 2017, one additional treatment was added, CE only, and CAU treatments were removed as they caused significant injury to the trees. Canker size was measured pretreatment, and the treated canker or excised area was measured posttreatment every 2 weeks for 13–15 weeks. Compared with pretreatment, cankers treated with BM did not increase in size, while the excised area treated with CAU increased 28-fold in size on average, and the excised area treated with 0.5% sodium hypochlorite or copper hydroxide increased up to 4-fold in size. Each year new cankers developed in all treatments 13–15 weeks after treatment application, at a time of year when there should not be any spores present to cause new infections. Dark brown streaking, indicative of the disease, was observed in the tissue below the intact or excised cankers 15 months after treatment application all years. Although N. malicorticis was not isolated from symptomatic tissue, symptoms were observed in all treatments including where cankers had not been excised and there was no wounding of the cambium tissue. Findings from this study indicate that of the treatments evaluated, the application of copper hydroxide after CE was the most effective for limiting the number of new cankers, but it did not limit expansion of the excised area. Additional physical and fungicidal strategies need to be tested for effective management of anthracnose canker.