The causal agent of gray mould, Botrytis cinerea, survives on dead crop residue. The spores are spread with the wind. Favorable conditions for infection prevail in wet weather and at temperatures of 10-15 °C. Sheltered sites and dense plant stands also contribute to infection. Grey mould is an opportunistic fungus. It prefers to colonize injured plant parts. It invades the stems via the petioles.
Grey mould (oilseed rape) [Botryotinia fuckeliana]
(Pictures 1 to 4) Symptoms can be found on all plant parts. With high humidity, a grayish-brown fungal lawn is discernible on the infection sites. The leaves initially show whitish-gray spots, which eventually turn pale brown or pale green they then wilt and die. Grayish spots develop on the lower portions of the stem, and eventually enlarge into infection areas that girdle the stem. The plant may break off. The infection on buds, inflorescences, and pods is expressed as pale yellow discoloration, wilting, and dying off. Grey mould (oilseed rape) can be confused with light leaf spot, Cylindrosporium disease, white leaf spot, white mold, stem rot, Verticillium wilt, or downy mildew.
Botrytis rot, causal agent: Botrytis cinerea (asexual form/anamorph)