All growers of roses know the devastating effects of Botrytis. Botrytis cinerea, which is its full name, is a fungus that causes flowers to turn brown and drop their petals. The infection starts with miniscule mould spores, spread through the air. Starting as a little white spot or ‘pock’ on the flower petals, it spreads right to the bottom of the flower. It gradually changes its colour to brown and finally all the petals fall off. In order to germinate, these spores need moisture.