On The Lookout: Daylily Rust
In 2000, a new fungus disease called daylily rust (Puccinia hemerocallis) began to attack daylilies nationwide. It will not kill an otherwise healthy plant but will make it unsightly and decrease its performance. The most obvious symptoms of daylily rust are yellow to brown streaks and small very bright yellow spots on the surface of the leaves. Small orange to yellow spots on the undersurfaces of the leaves contain pustules that release numerous dust-like, orange-colored spores. As symptoms progress, leaves turn yellow and dry.
Symptoms may be confused with aphid feeding or daylily leaf streak, caused by the fungus Aureobasidium macrostictum, but no orange pustules will develop from either of these organisms. Management of daylily rust depends largely on utilization of resistant cultivars and good sanitation practices. A list of resistant cultivars can be found here: http://edis.ifas.ufl.edu/pp172
Sanitation practices are important. Remove old leaves in the fall, disposing of them away from the growing site. Trim newly purchased plants to remove all foliage in the spring before planting. This will reduce the chance of introduction of the disease into landscape.
Both contact and systemic type fungicides are available for management of rust diseases. Contact products generally provide from 3 to 14 days protection and only protect those plant parts that are directly sprayed. Systemic fungicides move into the plant and can provide up to 21 days of protection from rust. Managing rust on the most susceptible cultivars often requires repeat applications of multiple products. A list of fungicide products labeled for rust diseases of commercial ornamental plants is available in the EDIS publication Professional Disease Management Guide for Ornamental Plants.