APS Abstracts of Presentations

Management of flyspeck disease of apple based on maturation of the causal agent (Schizothyrium pomi), wetting hours and fungicide properties
Presenter: D. Cooley, University of Massachusetts Amherst, Amherst, MA 01003
Co-Author(s): D. Rosenberger, Cornell University's Hudson Valley Lab, Highland, NY 12528
Phytopathology 95:S21

Summer fungicide applications on apple in the Northeastern U.S. primarily target a summer blemish disease complex in which flyspeck, caused by Schizothyrium pomi, is the most difficult component to control. Maturation of primary inoculum of S. pomi on natural reservoir hosts was monitored in MA over three seasons. Maturation was temperature driven and occurred over a single, discrete period roughly related to McIntosh apple phenology, beginning at bloom and ending two wk after petal fall. Orchard monitoring suggests that primary infections are limited to reservoir hosts adjacent to orchards, perhaps because fungicides protect apples or ascospore migration into orchards is minimal. Significant infection of apple fruit occurs only after conidia produced on reservoir hosts are blown into orchards. Field studies in southeastern NY verified that conidia usually do not reach orchards until the cumulative leaf wetting from McIntosh petal fall (CLW-PF) reaches 270 hr. Because kresoxim-methyl, trifloxystrobin, and thiophanate-methyl all have post-infection activity against flyspeck, fungicide sprays can be omitted during summer until the time that CLW-PF reaches 300 hr. This timing regimen should allow growers to omit one to two fungicide sprays during June and July in most years without significantly increasing the risk of flyspeck on fruit at harvest.

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