{"id":269,"date":"2026-06-18T23:09:34","date_gmt":"2026-06-18T22:09:34","guid":{"rendered":"https:\/\/www.coltivobio.com\/en\/?p=269"},"modified":"2026-06-21T12:33:21","modified_gmt":"2026-06-21T11:33:21","slug":"grapevine-downy-mildew-plasmopara-viticola","status":"publish","type":"post","link":"https:\/\/www.coltivobio.com\/en\/grapevine-downy-mildew-plasmopara-viticola\/","title":{"rendered":"Grapevine downy mildew (Plasmopara viticola)"},"content":{"rendered":"

Plasmopara viticola<\/em> is the causal agent of grapevine downy mildew, one of the most destructive diseases in viticulture. It is very difficult to control unless all preventive measures are implemented. This article describes the symptoms, damage, and biological cycle of downy mildew.\u00a0<\/strong><\/p>\n

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Disease identification and damage<\/strong><\/h2>\n

Grapevine downy mildew is caused by an oomycete (it was considered a fungus for a long time, but is now classified within the Kingdom Chromista) known as Plasmopara viticola<\/em>. It is regarded as one of the most dangerous diseases affecting grapevines. The pathogen attacks leaves, shoots, flowers, and fruits.<\/p>\n

The symptoms of grapevine downy mildew are quite characteristic. On the upper leaf surface, yellowish, translucent, and more or less circular spots can be observed (see photo below). These lesions are commonly referred to as \u201coil spots.\u201d<\/strong><\/p>\n

\"peronospora
Grapevine leaves showing clear symptoms of downy mildew. Note the yellow spots, which are characteristic of infection by Plasmopara viticola.<\/figcaption><\/figure>\n

On the lower leaf surface, directly beneath the oil spots, a white mildew develops (see photo below). This growth consists of the pathogen’s asexual reproductive structures. Eventually, the lesions become necrotic. In rare cases, the white mildew may appear without visible oil spots, or vice versa.<\/p>\n

\"peronospora\"
Downy mildew sporulation on grapevine leaves. At maturity, a characteristic white mildew develops on the lower leaf surface beneath chlorotic lesions. This growth contains the reproductive structures of Plasmopara viticola.<\/figcaption><\/figure>\n

In other cases, leaf infections may appear as a mosaic pattern, with numerous small yellow spots scattered across the leaf blade that later become necrotic (see photo below). This symptom is typical of late-season infections occurring in older leaves and is commonly referred to as mosaic downy mildew<\/strong>.<\/p>\n

\"peronospora
Mosaic downy mildew. Note the irregular and speckled appearance of the lesions. This symptom is characteristic of late-season infections caused by Plasmopara viticola. The typical white mildew still develops on the lower leaf surface.<\/figcaption><\/figure>\n

Affected inflorescences become covered with white mildew, which may eventually lead to the necrosis of the entire flower cluster (see photo below). In other cases, only the tip of the inflorescence is affected, becoming hooked and brown before being covered by white mildew.<\/p>\n

\"Symptoms
Symptoms of cluster downy mildew. In this case, environmental conditions were so favorable that the pathogen produced its characteristic white sporulation even on the berries.<\/figcaption><\/figure>\n

\"peronospora<\/p>\n

After fruit set, the pathogen begins attacking young grape clusters. In this case, the disease is referred to as brown rot phase<\/strong> or latent downy mildew<\/strong> (see photo below). Symptoms include browning, dehydration, and partial or complete drying of the cluster, resulting in the necrosis of individual berries. At this stage, the typical white sporulation is often absent because the stomata on the berry surface become non-functional as the berries develop. As a result, Plasmopara viticola<\/em> continues to grow and spread internally within the cluster tissues without producing the characteristic white mildew visible on leaves and young berries. This form of the disease is much more damaging than leaf infections because it directly affects the developing fruit and can significantly reduce yield and fruit quality.<\/p>\n

\"Latent
Latent downy mildew infection on a mature grape cluster.<\/figcaption><\/figure>\n

Biological cycle of grapevine downy mildew<\/strong><\/h2>\n

The pathogen overwinters as a sexual spore (oospore) within infected crop residues, particularly fallen leaves.<\/p>\n

Oospore germination occurs in spring when specific environmental conditions are met. These conditions are commonly known as the Rule of Three Tens<\/strong>:<\/p>\n