Prepared by Marjan Kluepfel and J. McLeod Scott, HGIC Information Specialists, James H. Blake, Extension Plant Pathologist, and Clyde S. Gorsuch, Extension Entomologist, Clemson University.(New 01/01.)
Diseases and insects generally are not a serious problem on daylilies (Hemerocallis species) in the home garden, especially when good cultural practices are followed. Daylilies prefer a well-drained soil with adequate organic matter. The use of a slow-release fertilizer is preferred. Planting daylilies too deep will result in reduced flowering and plant decline.
Leaf Streak: Daylily leaf streak is caused by the fungus Collecephalus hemerocalli. Symptoms are elongated brown streaks 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. To control leaf streak the fungicide thiophanate-methyl may be applied to slow disease development and to protect susceptible new growth from infection.
Root-Knot Nematode: Root-knot nematodes (Meloidogyne species) can cause loss of vigor and severe decline of daylilies. Infected plants slowly deteriorate, grow poorly and 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 you think nematodes are present in your yard, contact your local Extension office about testing procedures available. The best option is to choose plants that are not susceptible to the root-knot nematode.
Soft Rot: Erwinia carotovora causes bacterial rot at the base of the flowers and in the rhizomes. The bacteria that cause rot are normal soil inhabitants. Disease development is favored by high temperatures, poor air circulation, poor soil drainage and improper fertilization.
Prevention & Treatment: To prevent soft rot, avoid poor soil drainage by amending heavy clay soils with organic matter, avoid poor air circulation conditions in plant areas, avoid problem planting sites (do not plant susceptible daylily varieties in the same spot where plants show soft rot symptoms), permit wounded plants to heal (cork over) before planting, and do not fertilize or water too much. Discard all infected plant material.
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 fast-moving pests, you need a 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 in your daylilies, hold a sheet of stiff white paper under some leaves and flowers, and then strike 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 with petroleum jelly. Attach them to stakes and place near the daylilies.
If serious damage is occurring, insecticidal soap is recommended. As with any pesticide, read and follow all label directions and precautions.
Twospotted Spider Mites (Tetranychus urticae): The twospotted 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 as a result of the mite’s tiny size, this damage often goes unnoticed until 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, mites are very small and are difficult to detect before damage is obvious. To sample for mites in your 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, if started early in the infestation, is effective at controlling spider mites. 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) as a result of feeding on plant sap. The sooty mold fungus feeds on the honeydew, resulting in dark fungal growth, which is very unsightly.
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. As a result of their phenomenal reproductive rate, aphids are very difficult to control with insecticides. If a single aphid survives, a new colony can be produced in a short period of time. In addition, using insecticides means that beneficial predators will also be killed.
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. More information on control of slugs and snails is available in HGIC 2357, Snails & Slugs in the Home Garden.
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This information is supplied with the understanding that no discrimination is intended and no endorsement by the Clemson University Cooperative Extension Service is implied. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.