| Popis: |
Surveys of 112 commercial barley crops, yield loss experiments, and the assessment of 20 disease nurseries and 41 regional trials, from 1981 to 1986, showed that barley mildew is endemic throughout the agricultural areas of Western Australia, but seldom develops to epidemic proportions. Infection was common at the seedling stage with considerable variation in severity between and within farmers' fields, regions and seasons. The occurrence and severity of infection increased during the period of tiller production, but seldom developed further once tiller elongation commenced. The frequency with which severe infection persisted to anthesis was low and, with variation between seasons, was mainly confined to areas of extended growing season along the south coast. Infection of up to 70% leaf area damage resulted in a 40-60% reduction in grain yield. This reduction was due to reduced fertile tiller number if infection was severe during tiller production, or to reduced grain size and number if infection was severe at ear emergence and over grain filling. The overall economic importance of powdery mildew, however, is low even though the destructive potential of the disease can be high in some regions in some seasons. |
