Efficacy of Three Natural Chemicals to Reduce the Damage of Erysiphe cichoracearum on Chicory in Two Meteorologically Different Growing Seasons

In two meteorologically quite different years, 2002 and 2003, efficacy of three natural substances with a fungicidal activity (sulphur, soya lecithin, salicylic acid) for control of Erysiphe cichoracearum on chicory was tested. In a block designed field experiment, there were statistically significant differences in the mean index of infection of exterior leaves, in the mean total weight and mean net weight of the plants (¼ total weight ) weight of removed damaged leaves). There was also a significant difference in firmness of the heads of nine chicory varieties that was established in both years. In 2002, when no extreme weather conditions occurred, the fungus spread to a substantially larger extent. Yet no statistically significant differences were found in the efficacy of environmentally friendly fungicidal substances for control of the fungus. In the hotter and drier year of 2003, which was less favourable for spread of the pathogen, sulphur-containing fungicide was the most effective. In 2002, chicory yield was lower than in 2003. Generally, yield loss due to removal of damaged leaves was from 30.7 to 45.0% in the first year, and from 11.3 to 24.8% in the second. The highest mean total yield and net yield of chicory were in plants, which were treated three times with sulphur- containing fungicide. In 2002, the most firm heads were in plants treated with sulphur. In 2003, no significant differences among substances were detected. The most infected with the powdery mildew caused by E. cichoracearum, were the less productive varieties of chicory. A statistically significant relationship was not found between the firmness of the heads and the degree of infection. Among different parameters in this experiment, the only relevant and high statistically significant positive correlation (r2 ¼ 0.71) was determined between the total weight of the plants and yield loss of chicory due to infection with the fungus in question.