Fungus

The three most common types of fungal diseases that affect grapevines include powdery mildew, grey mold and downy mildew. Powdery mildew is caused by a fungal pathogen affects all parts of the grapevine but isolates most of its symptoms on the leaves. White colored patches will appear on younger leaves, with darker colorations on mature leaves; powdery mildew can also infect the berries and once this happens the fruit is more susceptible to be infected with other diseases as well.

Downy mildew presents itself as yellowed or browned leaves or berries and is especially prevalent in climates with cool temperatures and high humidity. Black Rot displays its symptoms as small brown-red spots that occurs on the leaves and as it continues to grow the borders turn black. The fruit will also start to shrink and mummify with lighter colored spots and black borders. Grey Mold, also known as noble rot, produces spores that enter the plant through lesions or wounds (typically caused by other fungi) and makes the flowers or berries soft and brown.

Other less common types of fungus include, mushroom root rot and cotton root rot (which affects the root systems), dead arm fungus (that affects the fruit), crown gall and anthracnose (both can be found throughout the vine).

All of these types of fungus can be treated with various fungicides and sprays that are usually applied before the bloom as a preventative measure. Some fungicides are only available to commercial growers, so for amateur viticulturists, removal of infected vines and some surfactants can be used to treat fungal diseases.