This disease is considered to be the major pest threat to mint production in the U.S. and is spread by the planting of contaminated material. Rust of mint, caused by the pathogen Puccinia menthae, is another major problem in several mint growing districts. Tilt is the only fungicide currently registered and is applied in the spring. Rally, another fungicide, will also likely be registered in the near future. Planting material originating from areas or fields infested with rust contributes to the spread and severity of this problem.
Powdery mildew is another concern to mint growers.
This disease is especially a problem in spearmint production, but has increased in severity in peppermint as well. Current control consists of multiple applications of elemental sulfur. Sulfur has been shown to eliminate beneficials, especially predator mites and also imparts undesirable flavor characteristics to mint oil. Rally, a fungicide which controls powdery mildew but does not harm beneficials, will likely be registered the near future. This disease is also spread by planting of contaminated material.