Gradients of Ascochyta Blight in Saskatchewan Lentil Crops. E. A. Pedersen, Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0. S. Bedi, and R. A. A. Morrall. Department of Biology, University of Saskatchewan, Saskatoon, Saskatchewan, Canada S7N 0W0. Plant Dis. 77:143-149. Accepted for publication 3 October 1992. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-0143.

Horizontal spread of Ascochyta blight was studied from 1988 to 1990 in 20 commercial lentil (Lens culinaris) crops planted immediately adjacent to residues of the previous year’s lentil crop. The percentage of seed infected with Ascochyta fabae f. sp. lentis was determined in samples collected at harvest. In several lentil crops in which treatments to reduce disease spread were imposed on the edge of the field, incidence and severity were also assessed. Usually, the disease was observed 20 m or more from the edge of fields early in the season, and incidence, severity, and seed infection declined sharply with increasing distance from the adjacent residues. Disease severity gradients reflected the pattern of local precipitation. Gradients became shallower, and disease spread was restricted, when limited precipitation occurred, particularly in July. Seed infection occurred up to 250 m from the primary inoculum source, but gradients generally leveled off within 50 m. Although fallow, nonhost, and fungicide treatments on the edge of fields did not reduce horizontal disease spread, they eliminated high levels of seed infection close to the inoculum source.