I put all my plants in a greenhouse to winterize. But now I see grey mildew on a couple of leaves. What do I have to do?
What you see is grey mould or Botrytis cinerea. It affects extinct herbaceous collenchyma of winterizing plants. What you now need to do is to control the leaves frequently and take off the affected leaves to get rid of the fungi. The ideal climate for fungi and grey mould is warm and humid. Therefore, you should also take care of good ventilation - whenever the temperatures permit - and keep sufficient space between your different plants.