Issue 4, May 14, 2010
Daylily Leaf Streak
Daylily foliage is looking lush in most parts of the state. In some of the wetter areas we have seen daylily leaf streak. This is a fungal disease, caused by Aureobasidium microstictum. The fungus is easy to confirm with a microscope, but spores are not really visible with a hand lens. For those of you interested in microscopic confirmation, view this article from the University of Florida (Adobe PDF). I have had the best luck viewing acervuli and conidia after the sample has been incubated for two days.
The symptoms include yellowing along the central vein of the leaf, small reddish brown, elongated spots in the yellowed areas, and possibly a yellow area around the lesions. Severely affected leaves, like those in the image, will shrivel and die. Symptoms are similar with daylily rust but you will see pustules in the affected area if rust is present. Daylily rust was a concern in 2000 but does not survive our winters.
The leaf streak fungus lives over the winter on old leaves, so removing dead foliage in the fall will help manage the disease. Resting bodies, called sclerotia, also may form and drop to the soil. Keep plants divided and thinned to allow quicker drying. The fungus spreads by contact and in splashing water. Do not work with plants when they are wet.
Although there is definite variation in varietal susceptibility, none of the daylilies is resistant. If you feel the need to control the disease with fungicides, trifloxystrobin (Compass) is available to commercial growers beginning when the symptoms first appear. Home growers might try thiophanate-methyl containing products or myclobutanil or daconil. Remember, the label must state that the product is registered for use on daylily or similar general ornamental wording.
While we are on the topic of perennial diseases, consider purchasing a copy of a new book, Diseases of Herbaceous Perennials, by Gleason, Daughtrey, Chase, Moorman, and Mueller. It has fantastic images and very useful information.--Nancy Pataky