Rhizoctonia is a fungus found in the soil. In potatoes, most damage is caused by sclerotia on the tubers (scab).
The quantity and vitality of the sclerotia determine the degree of infestation. A slight, almost invisible infestation on seed potatoes, for example, can cause considerable damage and, conversely, visible infestation does not always have to lead to problems.
The presence of sclerotia is determined from 100 tubers, which is the Rhizoctonia index. After that, the vitality aspect is determined. The combination of index and vitality together leads to advice on whether or not to treat the seed potatoes.
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