VEVERKA K., PALICOVÁ J., KŘÍŽKOVÁ I. (2008): . Plant Protect. Sci., 44: 127–137. The warm climate pathogen <i>Macrophomina phaseolina</i> (Tassi) Goid., which causes charcoal disease, has been reported in the Czech Republic since 1999. The aim of our work was to study the incidence of disease between 2000–2007 in the main sunflower growing regions and analyse the relationship between weather conditions and the occurrence of the pathogen. The first and highest incidence of disease was in the Žatec region. However, in the region south of Brno there was no disease in 2000, 2001 and 2003, and only individual low incidence in other years until 2007, when the disease was found in nine localities. The incidence of the disease is increasing year by year indicating a spread of the pathogen. The warm and dry periods throughout the end of July and August have promoted the disease. However in some years where weather conditions were favourable for the pathogen, in several cases no disease was found. It is assumed, that the pathogen was not yet present in these localities. Soil conditions are critical. Diseased plants are usually distributed in several dispersed groups in the stand, especially on higher and drier parts of the field. Disease is also often found on plants suffering from compressed roots. Diseased plants had poorly developed heads and seeds.

Brown patches of the size from several square metres to hectares or individual dying plants appeared in otherwise green stands. Affected plants wilt and ripen sooner than healthy ones, causing them to have smaller seeds or none at all in the central part of the heads. Under extreme conditions the plants wilt and die in early summer when they are less than 50 cm high. No infective agent was found as a causal organism. Disturbed plants root only in the upper 10 cm layer of the soil, or just below the surface. Poor soil structure and aeration are supposed to be responsible for limited root development. It prevents a sufficient supply of water to the plants during the hot and dry summer months and causes them to wilt. In contrast to cereals, winter rape and some other field crops that ripen during July, sunflower grows very intensively and needs a good supply of water even towards the end of August and in the first half of September. Thus, sunflower plants rooting only in the shallow uppermost layer of the soil suffer much more than other crops from hot and dry conditions.