|Daylily (Hemerocallis spp.) Leaf Streak|
Daylily (Hemerocallis spp.) leaf streak is a fungal disease caused by the fungus Aureubasidium microstictum. It is a fairly common foliar disease of daylilies with some varieties being more susceptible than others. In my own garden, the daylily pictured above is affected almost yearly. Yet only a couple feet away grows another variety which has never been bothered by the disease.
The fungus over winters in infected plant material. Then in the spring, spores are released from this material, during wet periods. Rain drops and over head watering splash the spores to nearby leaves, where they create new infections. Infections may continue throughout the summer months during warm, wet weather.
Damage is usually cosmetic and does not threaten the life of the plant, although the plant can become weakened in severe cases, due to reduced photosynthesis.
Symptoms: usually start off with water-soaked (dark green) spots, which later enlarge and brown, forming streaks along the midvein of the leaf. In severe cases the leaves yellow and brown, beginning at the tip working its way down the leaf.
Treatment: In most cases simply removing infected foliage is all that is required to control the disease. If the majority of the plant is affected, the entire plant can be cut back hard (nearly to the ground) and it will send forth new growth. (DO NOT compost the diseased leaves.)
Other helpful gardening practices include:
- Cut-back infected lilies in late autumn and dispose of the plant debris in garden waste. This will help to reduce over wintering spores.
- Reducing injury to plants; the fungus is thought to enter the plant through some type of injury, be it an insect (like thrips), a mechanical injury (like a lawn mower) or an animal.
- Divide daylilies as needed to prevent the planting from becoming overcrowded. Overcrowding slows leaf drying and favors the development of fungi.
- Water daylilies at the base of the plant to prevent water splashing.
- Remove infected leaves to slow the spread of the disease.
Note: daylily rust (as pictured here) looks very similar to leaf streak. This disease is caused by the fungus Puccinia hemerocallidis. Look for orange pustules on the undersides of the leaves.