Chrysanthemum white rust, caused by Puccinia horiana, is a true rust that is regulated by a federal quarantine. The disease has been seen only rarely in the Northeast, and must be eradicated whenever it is detected. One case of this disease was seen at a public garden in New York in 2019 and was eradicated. Mum growers should watch carefully for symptoms of this rust, because it is far easier to eradicate when it is still a localized infection.