Grapevine Downy Mildew

Plasmopara viticola

1. Identification

Plasmopara viticola is the causal agent of grapevine downy mildew, one of the most destructive diseases of the crop. It is known internationally as “grapevine downy mildew”, or “míldio da videira” in Portuguese. It affects leaves, inflorescences and bunches, and can completely compromise production in years favourable to the pathogen.

2. Causal agent

Oomycete of the genus Plasmopara, described by Berk. & Curt., belonging to the group of pseudofungi. It is characterised by the production of branched sporangiophores that emerge from the underside of the leaves, giving rise to the typical “white powder” of downy mildew.

3. Main hosts

• Grapevine (Vitis vinifera) — main host
• Some wild Vitis species may act as reservoirs
• Does not significantly affect other agricultural crops

4. Symptoms

• Oil spots on the upper surface of the leaves
• White efflorescence (sporulation) on the lower surface
• Necrosis and premature leaf drop
• Inflorescences and bunches with necrosis, wilting and drop
• Berries with brown rot and dehydration (“mildew berries”)
• In severe attacks, total loss of production

5. Disease cycle

• The pathogen overwinters in the form of oospores in the soil or in plant debris
• In spring, with rain and mild temperatures, the oospores germinate and release zoospores
• Primary infection occurs through water splashes
• Secondary infections recur throughout the season whenever there is: Wet foliage and temperatures between 10–25 °C
• The cycle is rapid and explosive under favourable conditions

6. Favourable conditions

• Frequent rain and prolonged periods of leaf wetness
• Mild temperatures (15–25 °C)
• Dense vineyards with poor ventilation
• Presence of oospores accumulated in the soil
• Humid springs and summers

7. Disease management

• Phenological monitoring and use of forecasting models
• Preventive treatments with authorised products, adjusted to the risk
• Good canopy ventilation through green pruning
• Soil management to reduce splashes (cover crops, grassing)
• Removal of infected debris after harvest
• Varieties with greater tolerance, when available
• Compliance with the integrated protection rules for the vineyard

Bibliographic references

• EPPO. Diagnostic Protocol PM 7/019: Plasmopara viticola.
• European Commission. IPM Guidelines for Grapevine.
• Agrios, G. N. (2005). Plant Pathology. Elsevier.
• FAO. Downy Mildew Management in Vineyards.