Seminar: Bitter Rot of Apple: Causal Fungal Species, Epidemiology, and Control Strategies

Phillip Martin, Graduate Student, Penn State
Phillip Martin

Phillip Martin

Date and Location

When (Date/Time)

January 28, 2019, 3:35 PM - 4:30 PM

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Bitter rot of apples, a fruit rot caused by fungi in the genus Colletotrichum, has become an increasing problem for apple growers in recent years with losses of up to 50%, depending on weather, apple cultivar and management strategies. Bitter rot was historically most problematic south of the Maryland to Ohio-river-valley line, and consequently, much of the current knowledge about bitter rot is based on research from those areas. Hypotheses for the increases in bitter rot in the Mid-Atlantic and Northeast include increases in temperature and humidity, fungicide resistance and fungicide labeling changes, and changes in orchard management. With a goal of identifying better bitter rot management strategies, research is being conducted on the fungal species causing bitter rot, the epidemiology of those species, and the efficacy of current control products. A survey of species causing bitter rot in PA and surrounding areas resulted in over 500 fungal isolates from over 30 orchards. At least 4 species have been identified, including one that has never before been reported as a pathogen of apple. Epidemiological studies have focused on the most common species, C. fioriniae. Spore trapping and quantification has shown C. fioriniae spores being dispersed from bloom through harvest, in both orchards and nearby forests. Detection of dormant bitter rot infections showed infections as early as late-May, even though rot was not obvious until August. Research on the sources of infectious spores and persistence of infected apples in the orchard is ongoing. Control product efficacy tests on C. fioriniae, and the second most common species, C. fructicola, showed minimal sensitivity to trifloxystrobin, sensitivity to fludioxonil, and mixed with thiophanate-methyl, with C. fructicola sensitive and C. fioriniae minimally so. Lab and field tests are ongoing to find molecular bases for insensitivity and identify efficacious control products.