Downy mildew of Parsley
Downy mildew of parsley is caused by a fungus-like organism called Plasmopara petroselini. It occurs in Europe and can causes crop losses of up to 100 per cent. It has not been reported in Australia.
Symptoms of downy mildew
White spots appear on the upper surface of leaves and as the spots enlarge, they become angular and turn yellow (Figure 1).
On the corresponding under surface of the leaf a white to greyish fluffy mat develops. This is the mycelium of P. petroselini (Figures 2 and 3).
Eventually the affected leaves and stalks rot.
Spread of downy mildew
The disease will rapidly spread in exceptionally warm and humid weather. The fungus requires living tissue to grow.
Spores are produced overnight on the under surface of leaf spots and released in the morning as the humidity drops. These airborne spores are dispersed by wind. They are deposited on the leaf surfaces and require water for germination and infection.
Resting spores (oospores) are produced in leaf tissue and survive in crop debris. It is not known if the disease is seedborne, but spores may contaminate the surfaces of seed.
Controlling downy mildew
- Avoid long periods of leaf wetness
- Increase ventilation
- Deter carry over of crop debris, which may contain fungal spores
- Plough in crop debris to encourage its decomposition and rotate ground out parsley crops.
Current situation in Victoria
Downy mildew disease in parsley has not been reported in Australia to-date. If you suspect you have downy mildew symptoms on parsley plants, please report to the Exotic Plant Pest Hotline.
Crepel C, Inghelbrecht S (2003) First report of Plasmopara petroselini on Parsley in Belgium. Diseases Notes 87 (10).
EPPO Global Database. Plasmopara petroselini (Plaspe). https://gd.eppo.int/taxon/PLASPE.
Soylu S, Soylu EM, Kurt S (2010) Downy mildew outbreak on parsley caused by Plasmopara petroselini in Turkey. Plant Pathology 59:799.
Figure 1, 2 and 3 courtesy of EPPO