Daylilies (Hemerocallis) are tough, reliable, low-maintenance perennials. Daylilies thrive in most average garden soils, preferring full sun and extra watering during dry spells. Though resistant to many of the bacterial, viral and fungal infections that attack other plants, there are fungal diseases that can adversely affect your plants. Good maintenance habits and early detection are the best ways to prevent significant disease damage to daylilies.
This fungus is the most common foliar disease of daylilies. In spring, wet weather causes the release of the fungal spores. Rain splashed on leaves permits new infections to spread. Infected foliage develops dark green water spots which eventually turn brown. The brown spots then enlarge, forming streaks which descend along the midvein of the infected foliage. Severely infected leaves turn yellow and may die. Leaf streak infections may continue throughout the summer, especially if the weather is hot and humid.
Daylily rust is a fungal disease that first appears as small water spots on the leaves, gradually progressing to powdery, orange-yellow blotches. Wiping the blotches away will reveal a white area underneath. Daylily rust is not usually fatal to the entire plant, but it can cause foliage to become withered and unsightly. Apply an appropriate fungicide either as a precautionary measure or at the first sign of disease.
This fungal disease causes discolored spots and blotches to appear on leaves. Infected foliage eventually turns yellow, withers and dies. Leaf spot occurs most frequently during warm, humid conditions and is spread by splashing water, wind, insects, and the use of previously contaminated tools. Pick off and destroy all severely infected leaves. Minimize overhead watering methods. Water the ground at the base of the plants to help avoid wetting the leaves. Weekly applications of fungicide during warm, humid weather can minimize the development and spread of leaf spot.
Good gardening and maintenance routines are the first and best defense against daylily fungal diseases. Choose disease-resistant daylily cultivars. Routinely deadhead to keep withered blooms from littering the ground. Keep garden area free of debris. Fungus spores left on plant debris are able to survive winter cold. At the end of the growing season, cut back and remove all infected foliage. Do not put diseased plant material in compost piles or bins. Most home compost piles do not sustain a temperature high enough to kill fungus spores.
Fungicides are very potent. Ask nursery personnel for advice, and choose the least toxic substance you can to prevent or control the problem. Read label directions thoroughly and use care when applying. Choose a product formulated for use on daylilies.