Factors Associated with Global Occurrences of Septoria nodorum Blotch and Septoria tritici Blotch of Wheat. S. Leath, USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. A. L. Scharen, R. E. Lund, and M. E. Dietz-Holmes. Department of Plant Pathology, Montana Agricultural Experiment Station, and USDA-ARS, Department of Plant and Soil Science, Montana State University, Bozeman 59717. Plant Dis. 77:1266-1270. Accepted for publication 15 October 1993. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1993. DOI: 10.1094/PD-77-1266.

Changes in incidence and severity of Septoria nodorum blotch (SNB) and Septoria tritici blotch (STB) have been noted in recent years in several wheat-growing areas of the world. A questionnaire was designed to identify factors associated with occurrence and development of these diseases. The questionnaire was sent to Septoria workers worldwide, and 71 responses were received and analyzed. The most important factors found relating to disease occurrence were: 1) latitude, 2) non-growing season precipitation, 3) growing season precipitation, 4) application of phosphorus, and 5) frequency of minimum or reduced tillage. Latitude effects were in agreement with general observations of SNB and STB occurrence. Also, growing season precipitation was important with regard to occurrence and severity of these diseases. Influential factors that were not expected were non-growing season precipitation and application of phosphorus fertilizer. Additionally, reduced or minimum tillage was shown to be negatively associated with disease levels, an effect opposite to that reported for other pathosystems under long-term controlled conditions. The study demonstrated the need for further investigation by a multidisciplinary team of scientists under long-term controlled conditions in order to understand the unexpected results of our survey.

Keyword(s): cereals, Leptosphaeria (Septoria) nodorum, Mycosphaerella graminicola.