Botrytis f
Symptomes :
§ Look for masses of brown-gray circular spots that later become fuzzy, producing masses of fungal spores. Tiny, black, shiny specks might also be seen embedded in diseased plant tissue. These are sclerotia of Botrytis: they allow the fungus to survive the winter. Botrytis blight can affect leaves, stems, crowns, flowers, flower buds, seeds, seedlings, bulbs, and just about any other part of a plant with the exception of the roots
Description :
Botrytis is often referred to as "grey mould", this is because it often looks like soft mould on plants. It is attracted to soft delicate plants, often seedlings and fleshy flowers. In the photograph you can see it is making the flowers of the polyanthus go brown. To try and prevent Botrytis, avoid letting susceptible plants get damp and cold for long periods of time.
  Solution :
§ Botrytis Blight (grey mould) can be controlled by § Spraying with a fungicide § Vigilant inspection of plants § Removal of any blighted flowers or leave § Removal of entire plants if they are infected at the base