Itersonilia canker, also called black canker, is caused by Itersonilia perplexans. Itersonilia canker of parsnip can be a serious disease, especially in late harvested crops. The pathogen also affects carrot, coriander, parsley, chrysanthemum, aster, sunflower and wild plants. Some pathogenic specialization has been reported as isolates from parsnip are not pathogenic to chrysanthemum and vice versa.
Roots, leaves, petioles, and inflorescences may be infected. On roots, cankers formmainly on the crown and shoulder, although lateral roots may be affected. Lesions are superficial and brown, black, or purple black. Secondary decay of cankers can occur. On leaves, symptoms occur as small orange to brown lesions with a pale green halo. Infected inflorescences may be completely blighted.
The pathogen is widespread as a leaf surface saprophyte (non-pathogen) on umbelliferous crops and members of the Compositeae. The fungus overwinters in infected parsnip roots or as chlamydospores in the soil. Spread within in a field is by windborne spores. New spores produced on foliage fall to the soil and cause root infections. Disease development is enhanced by cool, wet weather.
Cultural Controls & Prevention:
- Select and plant resistant cultivars.
- Rotate parsnip with non-host crops.
- Control carrot rust fly as larvae can predispose roots to infection.
- Fungicide sprays are not effective for control of root cankers.
- Cover the shoulder of parsnips with soil throughout the growing season.
- Reduce soilborne inoculum by deep plowing to enhance decomposition of parsnip residue.
Chemical Controls & Pesticides:
For current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website.