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New Daylily Pest Merits Attention, Not Panic

Report from the All-America Daylily Selection Council — January 2002

After nearly a century of trouble free garden beauty, America's most popular perennial finally has a problem worth mentioning. Puccinia hemerocallidis (daylily rust) has been found in over half of the States in the U.S. Puccinia spores spread quickly by wind, on clothing, and on infected plants, and can survive in USDA hardiness zone 2. Infected plants show unsightly rust spots and yellowing, mostly on older foliage, similar to rust symptoms on roses, geraniums, and other garden plants. No daylily plants have been killed by the rust.

Daylily rust does not affect other plant species. Roses have their own specific rust species, as do most other ornamental plants. Just as with roses, symptoms of daylily rust vary greatly depending on growing conditions and the susceptibility of each variety. Among the over 48,000 registered daylily cultivars are varieties that are virtually symptom free, and others that look so messy when infected that they will gradually be dropped from nurseries and private gardens.

Daylilies grown in areas with high humidity, poor air circulation and nighttime overhead watering will show the most symptoms. Since these conditions change seasonally, gardeners will often cut off unsightly foliage, which is quickly replaced by clean, new foliage. For years, many landscape professionals have "renovated" their daylilies by cutting them back in late summer, so this is not really a new practice. For those wanting to take more aggressive action, cut infested plants back to the ground, dispose of foliage and treat with a fungicide labeled for rust prevention, such as Daconil.

There are numerous groups diligently researching ways to treat daylily rust. An Internet search of "Puccinia daylily rust" will bring up an overwhelming amount of information. The All American Daylily Selection Council (AADSC) prefers to focus on identifying and promoting more rust-resistant daylily varieties.

Since 1989, the AADSC has operated a network of daylily test sites throughout the U.S. Data is collected on over 50 performance characteristics. Since last year, rust resistance has been added as one of the key test criteria. Preliminary information suggests that in selecting for "bulletproof" performance, the AADSC has eliminated many of the highly susceptible varieties from its program. The AADSC generally does not release conclusions about varieties until it has 3-5 years worth of information. When that happens, varieties will be ranked from "highly susceptible" to "highly resistant." In the meantime we are beginning to see which varieties are "more susceptible" and "less susceptible." We do not have enough information on 'Starstruck', but all other daylily varieties announced as All Americans appear to be "less susceptible." This includes 'Black Eyed Stella', 'Lullaby Baby', and the three winners for 2002, 'Bitsy', 'Leebea Orange Crush', and 'Judith'.