What Diseases Can Affect Daylilies?

Daylilies belong to the genus Hemerocallis and comprise a variety of cultivars. Flowers last only one day, but the plants consist of many branches filled with flower buds, which prolongs the blooming period for two to three weeks. Daylilies tolerate a variety of climates, light conditions and soils, making them hardy additions to the garden. These plants are regarded as low-maintenance and relatively problem-free, but diseases can be a problem. As with all plant diseases, treating the problem quickly helps the daylily retain its good health.

Lily rust, simply called rust, is a fungal pathogen infecting daylilies. The fungus Puccinia hemerocallidis is an airborne pathogen whose spores travel miles on the wind’s currents. The fungus can first show up on the leaves as spots. As it develops, an orange, rusty-looking powder forms on the leaves. Because it can form on the undersides of the foliage, rust can go unnoticed. Areas with mild winters can have year-round outbreaks of the disease. In colder areas the fungus can overwinter on the plant until warm weather returns. To check for rust, wipe the foliage with a paper towel and look for an orange residue.

Mild cases of rust do not seem to affect the long-term health or growth of daylilies. Some foliage may die back naturally due to the fungus. Trim off infected leaves and dispose of them in a plastic bag, do nothing at all, or spray the plant with a fungicide specific for use on daylilies.

Various conditions create rotting crowns and roots in all varieties of daylilies. Many fungi such as Erwinia, Armillaria, Fusarium and Phytophthora can all create rotting symptoms in the lily. Lilies infected with the disease usually emit a foul odor. Other signs of rot are decreased vigor, wilting and yellowing foliage, and the plant eventually turning to mush and dying. There are no treatments for rot once plants are infected.

Environmental and growing conditions play the biggest role in daylilies developing crown or root rot. Do not replant in areas where previous daylily crops have died of the disease. Overwatering plants or growing them in consistently wet soil promotes rot. The application of too much fertilizer and injury to the plant from gardening or lawn tools also can lead to the condition. The injured area opens up an entranceway for the fungus to enter. To decrease the possibility of daylilies developing rot, plant in well-drained soil, do not overwater or fertilize, and follow the particular cultivar’s growth and planting requirements.

Leak streak in daylilies, caused by the fungus Aureobasidium, generally enters the plant through a wound. Plants infected with the fungus show signs on their foliage by their centralized leaf veins turning yellow. The foliage eventually turns brown, with reddish, spotted areas joining together, leading to the eventual death of the leaf. You can reduce the likelihood of this fungus by minimizing overhead watering and not gardening around the lilies while the foliage is wet.