VIEW ARTICLE

Ecology and Epidemiology

Epidemiology of Spot-Type Net Blotch on Spring Barley in Saskatchewan. C. G. J. van den Berg, Department of Crop Science and Plant Ecology, and Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0, Present address: Department of Plant Science, University of Manitoba, Winnipeg R3T 2N2; B. G. Rossnagel, Department of Crop Science and Plant Ecology, and Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0. Phytopathology 81:1446-1452. Accepted for publication 2 July 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/Phyto-81-1446.

The number of airborne spores of Pyrenophora teres f. maculata, disease progress, and occurrence of conditions favorable for disease development were studied in relation to crop development and weather variables in a barley crop growing in a field with infested crop debris in 1986 and 1987. Conidia were trapped in both years, but no ascospores were detected. Daily number of airborne conidia followed a seasonal pattern. It was generally low during June, increased during July, and peaked about 1 August. The daily number of airborne conidia was correlated with the senescence of the upper leaves. Variation in daily number of airborne conidia was correlated with minimum and mean temperature on the previous and same day during June, and with maximum and mean temperature on the same day during July. No relationship was observed between daily number of airborne conidia and duration of leaf surface wetness during the growing season. The hourly number of airborne conidia followed a diurnal pattern, with a maximum at 1400 hours. The periodicity was associated with diurnal changes in temperature, relative humidity, and occurrence of leaf surface wetness. Combinations of temperature and leaf surface wetness observed on most nights during the growing season would allow infection. Consequently, progression of spot-type net blotch closely followed plant development, and each leaf was infected shortly after emergence.