Introduction Symptoms of the rust infection may not be present early in the development of the disease. The most obvious symptoms of daylily rust are yellow to brown streaks on the leaves. The plant veins tend to constrain fungal growth and make streaks. You may see very bright, small, yellow spots on the surface of the leaves. (Fig. 1). The undersurface of the leaves will have numerous small, orange to yellow spots, called pustules, that poke out of the undersurface of the leaf. The pustules grow and release numerous dusty, orange-colored spores. (Fig. 2). The orange spores are very dust like in nature and if you rub the leaf surface, will notice the dusty spores lofting about. As symptoms progress, leaves turn yellow and dry up.
It’s easy to confuse daylily rust with a couple of look-alike daylily problems. Daylily leaf streak, caused by the fungus Aureobasidium macrostictum, also causes similar symptoms of brown to yellow leaf streaks but it lacks the orange pustules that develop on the undersurface of the leaves. Aphid feeding damage can also look similar but again there are no pustules. Disease Cycle Heteroecious rusts produces 5 kinds of spores. Two of the spore stages
are of most concern with daylily rust, urediospores and teliospores.
The urediospores are the orange, powdery spores observed on the under
surface of the leaves. They have thin walls and spread the disease
during the normally mild summer months. Urediospores are capable of
re-infecting other daylily plants. The spores need 4-5 hours of moisture
to germinate and cause infection. Rainy overcast days are ideal for
spore germination and infection. Optimum temperatures are between
21-24oC (70-75oF)
but a slower germination can occur above and below that range. Germination
produces a germ tube that grows on the surface of the leaf looking
for access to the internal plant tissue. It often gains access through
natural openings such as stomata. Once in the plant, the fungus produces
additional spore stages that result in the production of more infectious
urediospores and possibily teliospores capable of infection alternate
hosts. Teliospores are found on daylily, have thick walls and exist
to survive the winter months. These spores are capable of infecting
the alternate host. Aeciaspores are formed on the alternate host and
are capable of infecting daylily. Severity varies with daylily cultivar. The rust mass grows below the outer layer or cuticle, then the blister forms below the skin. The pustule ruptures through the epidermis to release the powdery spores.
Management Strategies Very susceptible: Attribution, Colonel Scarborough, Crepe Eyed Ruffles, Double Buttercup, Flower Shop, Hello Sunshine, Imperial Guard, Irish Ice, Karie Ann, Lemon Yellow, Little Gypsy Vagabond, Lonesome Dove, Ming Toy, Pandora’s Box, Pardon Me, Patiencve Plus, Pink Beacon, Quannah, and Rosie Pinkerton, Royal Ebony, Russian Rhapsody, Silken Touch, Siloam Doolebug, Siloam Ralph Henry, Solomon's Robes, Splendid Touch, Springtime Treasurer, Violet Explosion, White Wow, and Woodland Romance.. Moderately susceptible: Butterflake, Crystal Tide, Gertrude Condon, Joan Senior, Prelude to Love, Star Struck, Stella D’Oro, and Wilson’s Yellow. Very resistant: Age of Gold, All-American Hero,
Antique Rose, Barbara Mitchell, Butterscotch Ruffles, Catherine Neal,
Creole Blush, Dainty Designer, Devonshire Cream, Ed Brown, Fashion
Design, Femme Fatale, Gentle Rose, Golden Maondy, Happy Returns, Heartfelt,
Holy Spirit, Joie de Vivre, Joleyne Nichole, Lavender Bonnet, Lilac
Lady, Mac the Knife, Mae West, Meadow Sweet, Neon Pink, Pink Flirt,
Prairie Blue Eyes, Raspberry Splash, Siloam Bill Monroe, Siloam Doulbe
Classic, Siloam Ury Winnifors, and Yangtze. 2. Sanitation: Clean up all plant residue in the fall. Remove all remaining foliage from the plants and remove it from the site. Burn or compost the residue, hot composts will kill the urediospores. Newly purchased plants can be pruned back in the spring, this may lessen your chances for introducing the pathogen into your garden from new plant material. 3. Fungicides that may be useful include some products that contain the active ingredients neem oil or thiophanate-methyl. Some of these fungicides are currently registered to treat rust diseases and/or Puccinia rusts on flowering landscape plants in New York State. Once an infection has become established, applications may be needed weekly because new infections are constantly beginning while plants are actively growing. Created, KLS, 8/02; Updated SLJ, 1/07 |
