Physan 20 is used as a fungicide on orchids, but has many other uses in the greenhouse as well. Here is an excerpt describing what it does:
Hope this hekps, Byron.Physan 20 is an effective control of fungi, algae, bacteria, and viruses. Use it as a general disinfectant for cleaning tools, benches, planter trays, contaminated pots and soil. Excellent for controlling bacteria and fungi on seeds, seedlings, cuttings and ornamental plants. Physan 20 can also be used to control algae in greenhouses, decorative ponds (TOXIC TO FISH!) and birdbaths. Or use it to treat a variety of diseases affecting lawns, turf, and grass, including fairy ring, dollar spot, and toadstools. Not intended for use on food crops. Most applications require less than 2 Tbsp. per gallon of water. Biodegradable.