Rusts are a group of fungi that cause disease on many plants including grasses, ohia, eucalyptus, guava, lemongrass and blueberries. It has long been a dreaded disease of wheat. In fact, rust disease on wheat is thought to be one contributing factor to the fall of the Roman Empire.
Plumeria rust first appeared in Hawai`I in 1994. It attacks the leaves and produces bright orange blisters on the underside of the leaf. These blisters rupture and release masses of orange colored spores. Heavily infected leaves can drop prematurely. The disease is rarely severe enough to cause serious damage to the tree and fungicidal applications are unnecessary. The problem is worse, however, in wet areas and during rainy periods. In dry areas where irrigation is necessary, the foliage should not be watered. Picking up dropped leaves and disposing of them will help to control the disease.