APS Abstracts of Presentations

Influence of environment on atmospheric concentrations of Alternaria panax conidia in cultivated American ginseng gardens
S. N. HILL (1), M. K. Hausbeck (1)
(1) Michigan State University, East Lansing, MI, USA
Phytopathology 96:S48

Leaf blight, caused by Alternaria panax, is the most common disease of cultivated ginseng and is an annual threat. To determine the influence of the environment on conidial occurrence and concentration, 2- and 3-year-old commercial American ginseng (Panax quinquefolium) gardens were monitored from mid-May to September for two growing seasons. Hourly concentrations of airborne A. panax conidia were enumerated using a Burkard volumetric spore sampler. The hourly averages of air temperature, duration of leaf wetness, rain, and relative humidity were also collected. Fungicides were not applied. The incidence of leaf blight and plant death were assessed in predetermined portions of each garden. Disease pressure from A. panax was high each year, and many plants were dead by late summer. In each year, the atmospheric conidial concentrations of A. panax were detected beginning late May and continuing through the monitoring period. Daily concentrations of atmospheric conidia followed a diurnal pattern and were greatest during periods of rapidly decreasing relative humidity. Weekly totals of conidial concentrations were greatest following rainy periods. The environmental influences on conidial concentration determined from this study will be used to develop a disease forecaster to reduce the number of fungicide sprays needed yearly.

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