So sorry but the fungus among us is growing rapidly in the cold, damp weather. Good air circulation and less humidity will help but you may need to cut back the infected leaves if you can so the mildew does not spread. Fungicides are available to spray on some plant crops but mildew is hard to stop once it starts. A fan in your greenhouse to move the air and less moisture from watering the plants will help. You may also want to consider a space heater to dry out the cool moist air. Good luck and remember to collect all fallen and infected leaves but do not compost. If you would like to write and tell us what plants are infected I can send advice about if you can cut them back to soil level and start fresh. Some plants such as houseplants respond to this drastic measure but others like seedlings will perish. Keep growing, Marianne Binetti