Genus name (botanically Botryotinia) for fungi with around 20 species that belong to the tubular fungi or moulds. All species live as parasites, which leads to the progressive decay of the tissue (rot) of the infested plants. The species Botrytis cinerea (also Botryotinia fuckeliana, grey mould, grey rot, grey mould rot, sour rot when grapes are still green) is a plant pest that attacks well over 200 host plants, including grapevines. The mycelium (fungal threads, tissue) is greyish or brownish. The fungus spreads mainly via conidia (asexual spore form). Some species can also reproduce sexually. Botrytis is one of the most economically significant harmful fungi in viticulture, as the infestation can cause considerable losses in quality as well as the basis for high-quality sweet wines, depending on the timing.

1 = Botrytis on the vine: Early infestation of the inflorescence with grey fungal turf and drying flower remnants
2 = Botrytis spores (conidia): Spreading form of the fungus, rapid spread through wind and moisture
3 = Grape botrytis (grey rot): Infestation of ripening berries with shriveling, rotting and grey mould coating

Occurrence

Botrytis was already described in the 18th century and occurs in all temperate climate zones of the world. Wine-growing regions with particularly favourable geographical and climatic conditions for infestation include Sauternes (France), Rheingau (Germany), Neusiedlersee (Austria) and Tokaj (Hungary). Flower bulbs, vegetables, ornamental plants and vines are particularly affected. In young grapes, the infestation has a necrotrophic (fatal) effect; in older grapes, the tissue remains viable for longer.

Infestation of the vine

All parts of the vine except the trunk and the perennial wood are attacked, but preferably flowers and (at all stages of ripeness) berries. This is because there is a sufficient supply of sugar and nitrogenous compounds on these. The name grey mould is derived from the characteristic grey fungal turf that covers the infested plant parts. Even a light breeze causes a grey cloud of fungal spores to rise, spreading quickly and widely and infecting other vines and plants.

A late attack on ripe berries from around 80 °Oechsle (16 °KMW) in dry autumn weather is ideal for noble rot. Prolonged rainfall from the end of August, dry and cool nights, during which fungal growth slows down, and warm and humid days of 20 to 25 °C, during which the fungus grows faster again, are ideal.

The fungus infects individual berries and spreads very quickly from there to the whole bunch. A second source of infection is infected, dead blossom remnants inside the grapes. Infections often originate from feeding sites of the caterpillars of the grape berry moth, which is otherwise feared in viticulture and through which the botrytis fungus can easily reach the inside of the berries. The picture shows botrytised grapes in three different stages.

Time point

Botrytis is feared in viticulture, but can be very desirable "at the right time". Depending on the stage of ripeness or the infested areas on the vine, there are also the self-explanatory terms botrytis on the vine, stem botrytis or grape...