Daylilies (Hemerocallis sp.) are popular garden plants grown abundantly by home gardeners, cities and commercial properties alike. Their appeal in part is due to their long bloom time, adaptability to a wide range of growing conditions and their relative ease of maintenance. There are a few foliar problems to be aware of, and while they seldom kill the plant, they can certainly mar the visual appeal of them. The first one, leaf scorch, is not a disease at all but rather an environmental condition. The second, daylily leaf streak, a fungal disease caused by the fungus Aureubasidium microstictum. The third is daylily rust caused by the fungus Puccinia hemerocallidis. The 3 disorders look fairly similar but there are differences and learning how to identify each will help you to manage them.

Leaf Scorch of Daylilies

Leaf scorch is a very common condition and is especially prevalent during hot dry weather. The condition is typically seen after a spell of cool cloudy days immediately followed by clear, bright sunny weather. Leaf tissue begins to die as the result of of water evaporating from leaf surfaces more quickly than the roots can replace. Even though the damage is physiological in nature there are a couple of factors that can contribute to the condition. The first is a deficiency in calcium. “Calcium transport to the leaf may be restricted by high humidity levels that slow the rate of transpiration. Since calcium is carried by the flow of transpiration, a slower rate of transpiration means less calcium reaching leaf tips. Low calcium levels in the young expanding foliage can induce tip burn and contribute to leaf scorch” (Plantlilies.com n.d.). The second factor that can contribute to the condition is excessive amounts of fluoride in the soil. Fluoride is a natural ingredient in superphosphate, it is also found in perlite and for some of us it is also in our tap water. In most cases daylily leaf scorch is considered a cosmetic problem and not a serious threat to plant health.

Symptoms:  Bleached or tan areas develop on the leaves that are especially prevalent at leaf tips. There will be splotching but no spotting as with rust and leaf streak.

Management:

• Keep the plants well watered especially during hot dry periods.
• Remove affected leaves to allow new growth to come from the base. Alternately the entire plant can be cut back to the base directly after flowering to allow for a second flush of healthy new growth.
• Prevent over crowding around daylily plants to ensure good air circulation that will help increase transpiration rates and the transport of calcium from the plant roots up to the leaf tips (Plantlilies.com n.d.).
• If your tap water contains fluoride, water your daylilies with rainwater. Avoid adding other sources of fluoride to the soil around your lilies such as super phosphate or perlite.

Daylily Leaf Streak

Daylily 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. The fungus survives winter in infected plant material. In the spring, spores are released during wet periods and rain splashed to nearby leaves, where they create new infections. Infections may continue throughout the summer months during warm, wet weather. The disease can also be spread by people, animals and pruning tools. 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: Look for yellowing along leaf midveins, often starting from the tip and moving down the leaf. Small, reddish brown flecks or spots develop that continue to enlarge. These enlarged specs are surrounded by yellow halos. In severe cases the leaves completely yellow and brown, beginning at the tip and working its way down the leaf.

Management: 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.)  

• Cut-back infected lilies in late autumn and dispose of the plant debris. 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.
• Disinfect tools that have come in contact with the plant.
• Avoid working in the garden when the leaves are wet.

Daylily Rust

Daylily rust is a fungal disease caused by the fungus Puccinia hemerocallidis. Daylily rust looks somewhat similar to leaf streak with spotting and yellow-to-brown streaks appearing on the leaves, but instead of reddish specks, the upper surface of the leaves may exhibit yellow spots while the underside develops yellow-orange, oval-shaped, raised pustules. (Note: The pustules can be found on both upper and lower leaf surfaces but tend to be more abundant on the lower surfaces.) These pustules fill with powdery orange fungal spores which can be carried on the wind or stick to anything that may touch them, including animals, your hand, clothing or tools. The veins of the leaf tend to prevent the fungus from crossing over, causing the disease to spread down the leaf forming streaks. The life cycle is really quite complex requiring 2 plant hosts and 5 different rust spore types to complete its life cycle. The other host plant being Patrina. Some varieties are more susceptible than others.

Biology and Life Cycle

The fungal spores overwinter in zone 7 and warmer areas (Bergeron S. rev. Feb. 2014). However micro-climates and other factors can contribute to the fungal spores overwintering in colder zones. In the spring the fungi produce special spores that are blown on the wind to infect its alternate host Patrina spp. The symptoms on infected Patrina spp. are similar, yellow spots that develop raised orangish bumps that are surrounded by chlorotic areas. By summer the pustules mature and fill with orange powdery spores that are blown on the wind back to susceptible daylilies. Note: in Ontario this occurs in the latter part of summer and early autumn (Celetti M. Et al. 2004). Under favourable conditions, symptoms appear 3-7 days after infection (Celetti M. Et al. 2004). Those favourable conditions are temperatures between 7-34^oC, with optimal temperatures being 22-24^oC, high humidity and a minimum of 5-6 hours of continuous leaf wetness (Celetti M. Et al. 2004). Infected daylilies develop yellow spots that develop oval-shaped raised bumps (pustules) within them. The leaf area around each pustule becomes chlorotic and often coalesce. The pustules fill with powdery orange fungal spores that when released continue to re-infect daylilies until temperatures drop below 7 ^o C. (Celetti M. Et al. 2004). The fungi then overwinter, and the cycle begins again.

Management

• Avoid growing Patrinia spp.
• Scout daylily plants frequently during the later weeks of summer, particularly after rain, when conditions are favourable for dew formation or during a prolonged period of cloudy days with daytime temperatures around 22-24^oC (Celetti M. Et al. 2004).
• Select varieties that are less susceptible.
• Avoid overhead irrigation and water in the mornings to allow the leaves to dry as quickly as possible.
• Avoid overcrowding to allow for good air circulation.
• If your lilies are infected with the disease cut the plants back to the base and burn or black bag the debris. Sterilize your tools after with rubbing alcohol or a solution of 1 part bleach to 9 parts water.
• Remove mulches near infected plants.
• Approved of fungicides can be applied to protect against infection beginning in early summer and may terminate when daytime temperatures do not exceed 7^oC. If they are already infected but are not yet producing powdery spore masses, systemic fungicides may be able to cure the infections and prevent pustule development. (Celetti M. Et al. 2004).

Summary

To keep your daylily plants healthy and looking good all season pay close attention to the weather and time of year. As soon as the temperatures begin rising and the rains subside be on the lookout for signs of leaf scorch on daylilies. Particularly after a spell of cool cloudy days immediately followed by clear, bright sunny weather. Keep the soil moist but the leaves dry. Ensure there is good air circulation around your lily plants to reduce the risk of fungal diseases. Beginning in the spring during mild wet periods begin regularly monitoring lily plants for signs of daylily leaf streak. Those signs are yellowing along leaf midveins, often starting from the tip and moving down the leaf. Reddish flecks appear that continue to enlarge and develop yellow halos around them. The leaves appear blotchy and streaky. Avoid injuring daylily plants during their infectious period. In early summer if daylily rust is a problem in your area begin protective fungicide treatments and monitor daylily plants for signs of rust. Those signs again are yellow/orange raised bumps with chlorotic areas around the outside that often coalesce. These bumps (pustules) fill with orange powdery fungal spores that easily coat the surface of anything that touches them. Continue to monitor lilies for signs of all three of these disorders throughout the summer and fall months.

Photo credits: all photos have been taken by the author.

Last updated on Mar. 4, 2022

References

Cornell University Plant Disease Diagnostic Clinic. KLS, 8/02; Updated SLJ 1/15. Daylily Rust: Puccinia hemerocallidis. http://plantclinic.cornell.edu/factsheets/daylilyrust.pdf

Celetti M. – Plant Pathologist/OMAFRA; Dr. Hsiang T.- Department of Environmental Biology/University of Guelph; Llewellyn J. – Nursery Crops Specialist/OMAFRA (2004, rev. 08/09). Daylily Rust Factsheet, http://omafra.gov.on.ca/english/crops/facts/04-089.htm

Meyers M. and Hudelson B. (rev. 4/24/2014). Daylily Leaf Streak. Item number:  XHT1235. Wisconsin Horticulture Division of Extension. https://hort.extension.wisc.edu/articles/daylily-leaf-streak/

Pataky N. 2007, Three Daylily Problems, Home, Yard and Pest Newsletter, University of Illinois. https://hyg.ipm.illinois.edu/pastpest/200711c.html

Plantlilies.com n.d., Leaf Scorch on Daylilies, https://plantlilies.com/lily-culture/pests/leaf-scorch-lilies.html

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