Daylily Diseases & Insect Pests

Diseases and insects generally are not a serious problem on daylilies (Hemerocallis species) in the home garden, especially when good cultural practices are followed. Because of the summer heat in South Carolina, daylilies should be planted in fall or spring. Daylilies prefer well-drained soil with adequate organic matter. Have the soil tested for the correct fertilizer analysis to use. Then apply a slow-release fertilizer in spring before they begin to bloom. Plant daylilies in a mostly sunny site. Planting daylilies too deeply will result in reduced flowering and plant decline. For more information on daylily culture, please see HGIC 1163, Daylily.

Diseases

Daylily leaf streak is caused by the fungal pathogen Aureobasidium microstictum.
Joey Williamson, ©2015 HGIC, Clemson Extension

Leaf Streak: Daylily leaf streak is caused by the fungus Aureobasidium microstictum. Symptoms are elongated yellow streaks along the leaf mid-vein followed by browning or spots on the infected leaves with yellow borders. These symptoms usually develop from the leaf tip downward. The infected leaves may wither and die completely.

Prevention & Treatment: Infected daylilies should be isolated from healthy plants. Daylily leaf streak may be avoided by purchasing disease-free stock plants and propagating only from healthy specimens. Avoid overhead irrigation. In the fall, remove dead foliage from around the base of the plants and dispose of the clippings, as the fungus will overwinter on senesced foliage, and spores will be produced the following spring to infect new leaves. Examples of resistant daylily cultivars include Betty Bennet, Edna Spalding, Ella Pettigrew, Globe Trotter, Nancy Hicks, Pink Superior, Ron Rousseau, Sudie, Tropical Tones, Upper Room, and Winsome Lady.

To control leaf streak, the fungicides thiophanate-methyl or myclobutanil may be applied to slow disease development and to protect susceptible new growth from infection. Begin sprays as new growth appears. Make 3 or 4 applications at 2-week intervals. See Table 1 for examples of products.

Daylily rust (caused by the fungus Puccinia hemerocallidis) showing erumpent orange pustules on the lower leaf surface.
Meg Williamson, ©2015 Clemson Plant Problem Clinic

Daylily Rust: Daylily rust is caused by the fungal pathogen Puccinia hemerocallidis. The symptoms are similar to those of daylily leaf streak: yellow to brown streaks on the leaves along with numerous, small yellow spots.

However, a distinguishing symptom with daylily rust is the appearance of small orange pustules that develop on the lower surface of leaves. These pustules produce the yellowish-orange urediniospores that spread to infect additional daylily foliage. These spores can be wind-blown or disseminated by gardeners handling infected plants. Daylily rust is capable of spreading quickly.

Prevention & Treatment: Inspect and purchase disease-free plants, especially the lower leaf surfaces. If rust-infected foliage is wiped with a white tissue, the spores will rub off and are visible as a yellowish-orange stain.

Check for and plant resistant cultivars. Avoid overhead irrigation. In the fall, remove dead foliage from around the base of daylily plants and dispose of the clippings.

To aid in the control of daylily rust, plants may be sprayed with propiconazole, myclobutanil, or chlorothalonil. Spray at 2-week intervals as needed, and additionally spray after cutting back plants. Do not spray chlorothalonil during the blooming period. See Table 1 for examples of brands and products.

Galls on roots infested with root-knot nematodes (Meloidogyne spp.).
Clemson University – USDA Cooperative Extension Slide Series, Bugwood.org

Root-Knot Nematode: Root-knot nematodes (Meloidogyne species) can cause loss of vigor and severe decline of daylilies. Infected plants slowly deteriorate, grow poorly, become stunted, turn yellow, wilt, and often die. The symptoms are very similar to moisture stress. Roots will often have small bumps or nodules where the nematodes feed and inject toxins.

Nematodes are most common in sandy, moist soils. They are generally more of a problem on former cropland that has been re-utilized for residential use.

Prevention & Treatment: If root-knot nematodes are suspected in residential landscape beds, plant samples may be submitted to the Clemson Plant and Pest Diagnostic Clinic through any county Clemson Extension office for verification. Because of the evident plant root galling by the root-knot nematode, entire plant samples should be submitted, not soil samples for assays as for other soil nematodes.

The best option is to choose plants that are not susceptible to the root-knot nematode. Remove and dispose of infested plants, but do not add them to the compost pile. For more information on symptoms of root-knot nematode damage and on control, please see HGIC 2216, Root-Knot Nematodes in the Vegetable Garden.

Soft Rot: Pectobacterium carotovorum causes bacterial rot at the base of daylily flowers and in their rhizomes. This bacterium that causes soft rot is a common soil inhabitant. High temperatures, poor air circulation, poor soil drainage, and improper fertilization all favor soft rot disease development. The crown (or base) of daylily plants with soft rot may have a strong, disagreeable odor.

Prevention & Treatment: To prevent soft rot:

• avoid poor soil drainage by amending heavy clay soils with organic matter (such as with composted pine bark or compost),
• avoid poor air circulation conditions in plant areas (prune back over-hanging shrubs),
• avoid problem planting sites (do not plant susceptible daylily varieties in the same spot where other plants have shown soft rot symptoms),
• permit wounded plants to heal (cork over) before planting, and
• do not over-fertilize or over-water plants (avoid over-head irrigation)

Discard all infected plant material.

Insects & Other Pests

Flower Thrips (Frankliniella tritici): Flower thrips and various other thrips species are serious pests of daylilies. Thrips are slender, dark-colored insects with fringed wings. Adults are less than ¹/₁₆-inch in length. To see these small, fast-moving pests, use a 10x magnifying lens. Thrips are typically found on leaves and between flower petals. Both adults and nymphs (immature insect stage resembling the adult, but smaller) feed by scraping surface cells to suck plant sap. When they feed on flower buds, the flower may die without opening. With a light infestation, their feeding causes leaves to have silvery speckles or streaks. With severe infestations, leaves and flowers are stunted and distorted and may turn brown and die.

Sampling: As a result of their small size, thrips are difficult to detect before damage is obvious. To sample for thrips on daylilies, hold a sheet of stiff white paper under some leaves and flowers, and then strike the paper with these plant parts. Gently tip the paper to remove any bits of trash and then examine the paper in bright sunlight. Any thrips present will move around on the paper.

Control: Several naturally occurring enemies feed on thrips. To avoid killing these beneficial insects, which naturally reduce thrips populations, insecticides should be avoided as much as possible. Blue sticky traps will help protect daylilies from thrips. Paint cardboard or wooden boards blue and then coat them with petroleum jelly. Attach them to stakes and place them near the daylilies.

If serious damage is occurring, insecticidal soap or spinosad sprays are recommended. Spinosad is a foliar systemic insecticide that can penetrate the unopened flowers to give good thrips control. Always spray in the evening to lessen the spray impact on pollinating insects. As with any pesticide, read and follow all label directions and precautions.

Two-spotted Spider Mites (Tetranychus urticae): The two-spotted spider mite and other mite species can be a problem on daylilies. Mites are not insects but are more closely related to spiders. They are very small, less than ¹/₅₀-inch long. They have piercing mouthparts that allow them to puncture plant tissue and suck plant sap. Mites tend to be more of a problem during hot, dry periods. Over time, some spider mites produce a fine web on leaves, which protects their eggs and young. With a light infestation, daylily leaves and flowers develop yellowish speckles. Partially because of the mite’s tiny size, this damage often goes unnoticed until the damage is more severe. With a heavy infestation, the speckles will run together, and entire leaves can become bleached and die. Along with leaf decline, growth is stunted.

Sampling: Like thrips, spider mites are very small and are difficult to detect before damage is obvious. To sample for mites on daylilies, follow the same procedure discussed in the thrips section above.

Control: Spider mites overwinter (survive the winter) on weeds, such as chickweed. Removing nearby weeds before spring growth is an important step in the control of spider mites. Insecticidal soap spray, if started early in the infestation, is effective at controlling spider mites. For more severe infestations, tau-fluvalinate or bifenthrin sprays will control spider mites. See Table 1 for examples of brands and products. As with all pesticides, read and follow all label directions and precautions.

Aphids: Various aphids can be pests on daylilies. Aphids are soft-bodied insects that vary in color from yellow-green to almost black. They are typically more of a problem during cool weather in the spring. They feed on leaves and flower buds by inserting their mouthparts and sucking plant sap. Their feeding can result in deformed leaves and small warty growths on flower buds. Most aphids excrete honeydew (a sugary liquid waste) after feeding on plant sap. A fungus called sooty mold will grow on the honeydew and result in dark fungal growth on the foliage.

Control: Several naturally occurring enemies feed on aphids, including green lacewings and ladybird beetles (ladybugs). As much as possible, these predators should be allowed to reduce aphid populations. Because of their phenomenal reproductive rate, aphids are very difficult to control with insecticides. If a single aphid survives, a new colony can be produced within a short time. In addition, the use of contact insecticides may also kill the beneficial predators of aphids. Insecticidal soap sprays are a less toxic alternative that can help reduce aphid populations.

However, for more severe infestations, bifenthrin, cyfluthrin, lambda cyhalothrin, or permethrin sprays will control aphids. See Table 1 for examples of brands and products.

Slugs & Snails: These can be a problem on daylilies, especially in the early spring when they feed on tender young growth. Their feeding results in ragged notches along leaf edges and sometimes holes in the middle of leaves. The appearance of shiny, slimy trails is a typical sign of their presence. Slugs and snails feed at night and hide during the day in moist areas.

Control: Remove their daytime hiding places by removing mulch and leaf litter near the base of the plant. Apply environmentally safe snail and slug baits (containing iron phosphate) near the beds. More information on control of slugs and snails and the safest baits is available in HGIC 2357, Snails & Slugs in the Home Garden.

Daylily leafminer (Ophiomyia kwansonis) damage is more aesthetic but not extremely significant to plant health.
Joey Williamson, ©2015 HGIC, Clemson Extension

Daylily Leafminer: The daylily leafminer (Ophiomyia kwansonis) was introduced into the US around 2006 from Japan and Taiwan and has quickly spread over the Eastern US. The leafminer adult is a small black fly, which oviposits (lays) its eggs on daylily foliage in the spring. The small pale-yellow larvae then feed within the leaves in meandering mines that become wider as the larvae grow. The whitish mines remain visible throughout the life of the leaf, which makes infested daylilies unmarketable. This pest over-winters as small tan pupae, approximately the size of a grain of rice. Over-wintering occurs either near the base of the leaves or at the base of the plants.

Control: Prompt removal and disposal of infested foliage will reduce the spread of this pest. Clean up and dispose of all dead foliage at the end of the season, as this will help reduce over-wintering of the pupae, as well as reduce the spread of foliar diseases, such as daylily leaf streak and daylily rust. Sprays to control the leafminer may affect natural predators and parasites that can reduce the number of leafminers.

Insecticides that control this leafminer are imidacloprid sprays or plant drenches, acephate sprays, or spinosad sprays. Spinosad is a natural product that is the safest to apply, and like acephate, is a foliar systemic insecticide. This means it will penetrate the foliage to kill the larvae within the leaves. Spinosad is used to control insect pests, including thrips, caterpillars, and flies, so it is less harmful to many beneficials. However, it is always best to spray late in the evening to reduce the impact on pollinating insects. Spray with spinosad as soon as symptoms of mining are noticed.

Table 1. Disease, Insect Pest, & Mite Control on Daylilies

Pesticides are updated annually. Last updates were done on 10/24 by N. Jordan Franklin.

Originally published 01/01