Elongated light-colored spots are visible after bloom. They first appear on one side and later surround the stem. The infection spreads from the leaf and stem axils.
White mould (oilseed rape) [Sclerotinia sclerotiorum (Raphanus)]
The spots appear pale yellow to whitish, with grayish centers (Picture 1). The cortex and pith of the stem are destroyed by the fungus, causing the branches and pods above to die. The infected plants with whitish stems are readily distinguished from the green, healthy plants. Light gray, irregularly-shaped dormant fruiting bodies that eventually turn black can be found in the interior of the stem (Picture 2). Except for a small amount of cottony mycelium, the stems are hollow. Infected pods are pale yellow and desiccated. Small sclerotia can be found between the seeds in the pods. In the early stage of stem infection, white mold can be confused with gray mold disease.
Observe 3-year rotation breaks. Weed control throughout the entire rotation sequence (broad host spectrum). Avoid excessive plant densities. Calcium cyanamide applications between February and the beginning of April. After harvest or before rape sowing: biological control is possible with the fungus parasite Coniothyrium minitans.
Fungicide seed treatment to control seedbourne infection: Fungicide application from beginning of flowering to full bloom (ES 61-65). When applying fungicides mixed with an insecticide, take foraging bees into consideration.
Spread/transmission: The fungus, which can survive in the soil for 7 to 10 years in the form of sclerotia (dormant bodies), can infect the plant at the soil surface or in the uppermost soil layers. Adequate soil moisture and temperatures of 7-11 °C are necessary for germination. Small, light brown, trumpet-shaped fruiting bodies emerge from the sclerotia and release ascospores. These spores are transported by the wind to rape leaves and stems. The fungus germinates and sporulates when the rape is in flower. Some of the fallen petals collect in the leaf and stem axils and serve as a breeding ground. Wet-foliage periods of 16 to 24 hours, 85% relative humidity, and temperatures between 0 and 25 °C are required for infection. Warm and periodically wet weather while the rape is in flower thus constitutes favorable infection conditions. Direct infection of the plant by mycelium is also possible but less common. The mycelium develops in the upper soil layer and infects roots and stem tissue. In the interior of the stem, a mycelium starts to develop and eventually forms dense, compact sclerotia. During harvest, the sclerotia fall to the ground along with the harvest residue and are able to infect new plants.