Correlation of wheat dwarf incidence to winter wheat cultivation practices

Wheat dwarf is a relatively uncommon, but potentially serious, disease of winter wheat. It is caused by wheat dwarf virus (WDV), a leafhopper-transmitted geminivirus. In 1997, an epidemic occurred in Central Sweden for the first time in 50 years. Farmers were requested to estimate yield losses and provide field data from infested fields. By analysing questionnaire data and results from field trials, the influence of various agronomic factors on disease intensity was assessed. Mean yield losses due to wheat dwarf reached 35%, with loss estimates up to 90%. The results show that early sown fields suffered more from wheat dwarf than fields sown at the normal time. A few other agronomic factors were also related to higher yield loss, e.g. presence of crop residues at sowing and irregular seedling emergence. Field trial data indicated a higher occurrence of disease symptoms in thin stands compared to dense crop stand canopy with differences in disease severity among cultivars. The study demonstrated the value of combining data from surveys and field trials for disease management studies, especially in the case of disease epidemics occurring infrequently. (C) 2002 Elsevier Science B.V. All rights reserved.