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Mycologia, ASCOMYCOTINA, DIAPORTHALES, VALSACEAE .
Identification, Description, Biology, Epidemiology, Treatement, Possible misleading, Images
[R]Description
On leaves brown necrotic triangular lesions occur at the edge of the leafblade and over a vein end which then extend towards the petiole. The leaf dries out but stays attached to the stem.
The fungus gradually infects the stem from the junction of the leaf at the stem. The necrosis on the stem spreads wide to girdle the stem and also extends up and down the node.
The main loss is shrivelling of the capitula and lodging of the stems which break at different levels.
On stems small black dots (picnidia) occur on the lesions.
[R]Biology
The fungus overwinters as mycelium and perithecia on stem debris left on the soil.
Perithecia form in late winter. From their elongated neck ascospores are released as a yellowish jelly soluble in rainwater.
The first contamination of the leaves by ascospores can occur in early spring. The first resulting lesions on the stems carry pycnidia with two kinds of pycnidiospores.
These conidia do not seem to influence the outbreak of the disease.
[R]Epidemiology
Temperature must reach 10 °C. for the first perithecia to occur after the first frost.
Ascospores are released when there are important variations in soil moisture.
Contamination of the leaves requires high RH (90%).
[R]Treatement
Grind and deep plough the stem debris.
Avoid tight sowing in high risk areas.
HYP3 on line : Species (scientific name), Diseases (common names), Glossary, Crops.
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