Question
Wayne-I live in the tropics and grow orchids outside 12 months a year.  Lately I seem to be battling fungus.  I have been treating them with several different fungicides, both preventative and systemic.  My question is this, is it absolutely necessary to remove all leaves that have been affected by the fungus?  After treatment, is the fungus dead on the leaves that were affected?  I have been removing leaves little by little,  but not sure how important it is if the orchids have been treated with systemic fungicide. Can it still spread?

Answer
Kristin, one of the most difficult issues with fungus is the spread of the fungus by means of spores which become airborn, land on other parts of the plant or travel to nearby plants where, when the environment is moist enough, can germinate and perpetuate the cycle. So, the fungal hyphae may be dead after treatment, but spores are very resistant to fungicides.  I use a combination of treatments to reduce and/or prevent damage from fungal infection.  I would remove any plant tissue that shows signs of damage from fungal infection as spores may still be present on the infected tissue. Second, I prefer to spray the plant with a copper based fungicide such as Kocide which coats the leaf and will kill any germinating spores. It may take repeated applications of either a systemic or surface fungicide to be sure to destroy the new growth from fungal spores. Even systemics have a limited lifetime and systemics are only effective on actively growing parts of the plant that take up the fungicide and incorporate it into their new tissues.  My main focus is to produce new plant tissues which are disease free.  Finally, especially humid areas, such as the tropics, create conditions ideal for fungal growth.  The best counter measure is to increase air circulation which can promote evaporation of moisture from plant surfaces-- keeping them drier.