Cuprofix Ultra-40 is a great way to control bacterial black spot and mildew. It works upon contact and does not appear to have any negative affect with most orchids: Cymbidiums, Cattleyas, Dendrobiums, Vandas, and Oncidiums all respond well. However, I would not advise using it on any orchid spp. that requires ultra clean water, like Draculas. The recommended amount used by the label is ¼ teaspoon per gallon, so a little will go a long way! This product is also on the list as an acceptable fungicide for organic farming.