Daylilies are low-maintenance perennials, with few disease problems. Most diseases can be prevented or solved by good gardening practices. Daylilies bloom best in full sun, but will grow in partial shade, as well.
The most common problems afflicting daylilies include daylily rust, oedema, nematodes and powdery mildew, according to Cornell University.
Daylily rust causes yellow or brown streaks and dusty, orange-colored spores. Oedema causes small, hard blisters on the leaves and stems. Nematode infestation causes root decay, stunted growth or deformed leaves. Powdery mildew causes a dusty white or gray powder to form on the leaves.
Good cultural practices help prevent many disease problems. Gardeners in hot, humid climates should always water early in the morning, instead of at night, so leaves dry quickly. Soaker hoses instead of sprinklers keep leaves dry, as well. Gardeners should remove dead or diseased leaves and stems from the plant, as well as the ground. Daylilies are fairly drought tolerant. Soil should be kept evenly moist, to slightly dry. Fungicides containing neem or potassium bicarbonate may treat Daylily rust or powdery mildew. Additionally, planting disease-resistant varieties minimizes the risk of disease, Cornell University advises.