How to Treat Leaf Rust Disease in Plumeria
Plumeria (Plumeria spp.), commonly known as frangipani or temple tree, is prized for its fragrant, attractive flowers in U.S. Department of Agriculture plant hardiness zones 10 and 11. One of the most prevalent diseases of this popular landscape plant is plumeria rust, which is caused by the fungal pathogen Coleosporium plumeriae. The disease appears as small light-colored spots on the upper leaf surface and abundant yellow-orange pustules of powdery spores on leaf undersides. Severely affected leaves become dry and brown, curl up and drop prematurely. A heavily affected plumeria can lose nearly all its leaves.
Pull out, mow down or otherwise control tall weeds that grow under or near the plumeria. Removing weeds from the area around the plumeria improves air circulation and reduces moisture around the plumeria foliage, discouraging rust spread.
Inspect the plumeria regularly for signs of rust beginning early in the growing season or shortly after the leaves emerge. Look for chlorotic spotting -- areas where the leaves lose their green color -- and yellow-orange growth. Pick affected leaves off before spores are produced and destroy these leaves.
Rake up and destroy fallen, diseased leaves promptly and rake up and dispose of all fallen leaves at the end of the growing season when they drop normally.
Spray the plumeria foliage thoroughly with a fungicide. Various active ingredients including coppers, mycobutanil and azoxystrobin can control rust on plumeria. Follow manufacturer directions for use on ornamentals. One manufacturer, for example, recommends mixing .5 to 2 fluid ounces of its liquid copper concentrate into 1 gallon of water, spraying the mixture so it completely coats both leaf surfaces and repeating the application every 7 to 10 days.
Remove and replace plumerias that are consistently bothered by rust even where you have taken all other possible measures to curb this disease. Choose other plant types, as the rust pathogen that attacks plumerias does not infect other plants. Within the genus Plumeria, Plumeria stenopetala and Plumeria caracasana are highly resistant to rust.
Fungicides to address rust on plumeria are rarely necessary, as the rust is typically not serious. However, fungicides are effective and warranted when rust had a serious impact in the previous growing season.
Always handle and apply fungicides carefully and according to manufacturer recommendations. Wear gloves and use a disposable face mask or other protective garments or equipment if the product instructions recommend it. Keep the fungicide away from children and pets and choose a fungicide formulation that is relatively safe. One good indication of a product's acceptability for use around children and pets is the minimum amount of time required between application and harvest, as stated on the label, when applying the product to vegetables and fruits -- a short time is preferable.
Before treating the entire plumeria with fungicide, test the product on a small, inconspicuous area and monitor that spot for injury for about a week before spraying the entire tree.