Listerine is a readily available home remedy which may be used on orchids. The original (gold colored) Listerine has anti-fungal, and probably anti-bacterial qualities. The high alcohol content makes it also effective against bugs. Since it is fairly weak, it is largely used by the growers on this site as a preventative, particularly when potting, or as something in a pinch until you can get something better. It is used full strength as a spray on, and should not be used for prolonged periods ...