MITIGATING FUNGAL DISEASE PROBLEMS IN SMALL FRUIT AND HOP CROPS USING AN INTEGRATED APPROACH

OBJECTIVES:The main goals of this project will be to:Address fungicide resistance in Michigan blueberries and grapesIdentifying new management practices for emerging diseases in Michigan hopsFungicide resistance in blueberries. A number of control failures have occurred over the years, particularly with anthracnose fruit rot with little understanding as to why it has occurred. Preliminary evidence suggests that fungicide resistance may be contributing to control failures. Resistance has been reported in C. acutatum, for example, in strawberries over 90% of isolates collected in 2013 and 2014 were resistant to a quinone outside inhibitor (QoI) fungicides (FRAC 11) (Forcelini et al., 2016). These mutations were primarily driven by two amino acid changes F129L and G143A. To compound the situation, the same researchers observed a general lack of fitness penalties and stability of the G143A mutation in QoI-resistant C. acutatum and further reintroduction of QoI fungicides might not be an option for growers (Forcelini et al., 2018a). Resistance to other chemistries has also been reported for DMI fungicides (FRAC 3) in blueberries but the mode of action is less clear but likely linked to the CYP51 gene (Chen et al., 2016). In 2014, a few MI isolates of C. acutatum were identified as resistant to FRAC 11 fungicides but results were not pursued further (Gillett et al., unpublished). If resistant isolates are not highly prevalent in MI, generic fungicide products for the fungicide azoxystrobin (FRAC 11) would be effective at controlling anthracnose, unfortunately, for MI this information is not available. Future work should investigate the population that currently exists within MI in terms of virulence and fungicide resistance, develop and implement diagnostic tools to track resistance. Grapevine powdery mildew fungicide resistance. The effectiveness of grape powdery mildew management programs is now threatened by the presence of Erysiphe necator (causal fungal agent) isolates resistant to both DMI and QoI fungicides. Approximately 98% of isolates tested from samples collected in OR, WA, and CA in our preliminary studies were resistant to either DMIs and QoIs with 62% resistant to both chemistry classes. We have also found one population resistant to aza-naphthalenes (FRAC group 13) and have anecdotal evidence that resistance to succinate dehydrogenase inhibitors (SDHI; FRAC group 7) is likely present in some E. necator populations in California and Oregon. These results indicate that field-level fungicide resistance to most of the available fungicides is likely to develop in the coming years across the US including MI; the industry will need to develop procedures to mitigate product attrition and crop loss due to fungicide resistance. Identifying and managing emerging diseases in hops. Grower recommendations for DM and PM control currently do exist within MI, but limited information is available about various fungicide programs. In 2018, a significant amount of blight was observed on hop foliage and cones that had not been previously reported in MI. The foliar and cone blight was observed on mature plants as well as new plantings that were in close proximity to mature plantings suggesting a risk of spread. Preliminary evidence suggests certain cultivars might be more susceptible (Higgins and Miles unpublished). Further evidence indicates that growers may have used suboptimal fungicide applications and inappropriate fungicide timing when controlling PM, leading to the development of this blight (M. Gura, Hop Head Farms, personal comm.). In culture, this fungus produces pycnidia and sporulates profusely. Preliminary analysis indicates it is a Diaporthe spp. (anamorph Phomopsis), however, more molecular markers are required to identify the fungus. Koch's postulates has been conducted and a detached leaf assay has been developed to study this pathosystem.