Be on the Watch for Daylily Rust

Features that make daylilies a favorite to grow are dependability as perennials, hardiness, and the fact that they are prolific bloomers. They are tolerant of drought and flooding; immune to heat stress; tolerant of most soils, full sun, or light shade; and they do not require fertilizer. They can be grown in most areas of the country, make excellent cut flowers, and have edible flower heads. The foliage also is quite attractive, offering an interesting textural contrast to other fine- foliaged perennials.

Previously considered relatively free of pests, daylilies now have a major disease problem. Daylily rust, caused by the fungus Puccinia hemerocallidis, was identified on daylilies in southeastern U.S. in the summer of 2000. In addition to a rapid incubation period (2 to 3 days), this disease spreads quickly. To date, known infections have all been on the daylily foliage and flower scapes, not the tuber.

Daylily rust is easily identified by localized, small orange to yellow-orange “blisters” (pustules) that contain orange, dust-like spores. These pustules are located primarily on the underside of leaves. The affected leaves discolor as they dry up.

To distinguish between daylily rust and daylily leaf streak (another fungal disease), simply scrape a pustule with your finger. An orange streak of spores is very diagnostic for daylily rust.

Rusts require an alternate host to complete their life cycle. In this case, the alternate host is Golden Valerian (Patrinia sp.), an ornamental perennial plant. Although the alternate host is not required for infection of daylily, you can reduce the disease pressure by not growing daylilies and Golden Valerian in the same landscape

Daylily rust can also be managed with timely, season-long applications of fungicides. However, use of disease-resistant cultivars is preferred. It is a good precaution to remove any infected foliage from the garden to reduce the inoculums the following year.

Kathy Nelson, Bedford Area Master Gardener