FACTORS ASSOCIATED WITH GLOBAL OCCURRENCES OF SEPTORIA-NODORUM BLOTCHAND SEPTORIA-TRITICI BLOTCH OF WHEAT

Changes in incidence and severity of Septoria nodorum blotch (SNB) and Septoria tritici blotch (STB) have been noted in recent years in seve ral wheat-growing areas of the world. A questionnaire was designed to identify factors associated with occurrence and development of these d iseases. The questionnaire was sent to Septoria workers worldwide, and 71 responses were received and analyzed. The most important factors f ound 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. Latitud e effects were in agreement with general observations of SNB and STB o ccurrence. Also, growing season precipitation was important with regar d to occurrence and severity of these diseases. Influential factors th at were not expected were non-growing season precipitation and applica tion of phosphorus fertilizer. Additionally, reduced or minimum tillag e was shown to be negatively associated with disease levels, an effect opposite to that reported for other pathosystems under long-term cont rolled conditions. The study demonstrated the need for further investi gation by a multidisciplinary team of scientists under long-term contr olled conditions in order to understand the unexpected results of our survey.