Mildew growth is an ongoing problem. Fungal spores land on surfaces and, under the right environmental conditions, grow. Ideal conditions are warm, moist climates, oxygen, and a substrate that serves as a nutrient source for mildew. Mildew growth on finishes causes discoloration and premature failure of the finish. Prevention of mildew can be done by pretreating the wood with a preservative that contains a mildewcide. Removal of mildew is achieved by using appropriate cleaning solutions. Finishes that contain synthetic mildewcides, with or without zinc oxide, help the finish resist mildew growth.