Pests, Diseases, & Problems Of Daylilies

Pests

Many daylily growers, breeders and display garden owners now find that as long as they practice good husbandry, in the long run their daylilies are better off not being bombarded with pesticides. Overuse of chemicals does not allow a plant to build up a natural resistance to pests and diseases, and also discourages natural predators. However, in times of serious infestation or disease some remedies are essential for the well-being of the plant.

Aphids (Myzus hemerocallis)

This pest usually feeds on the growing buds causing a wart-like appearance. Infested plants usually start late into growth with the new foliage being yellowed, giving the appearance of a nitrogen deficiency.

Bulb mite (Rhizoglyphus spp.)

These tiny insects can only be seen under a powerful microscope as they are only 0.3 to 0.5mm long. They feed from fungi on damaged bulbs or roots. There is no chemical control as yet but healthy plants are less likely to succumb to an invasion.

Earwigs

Earwigs eat the base of the anthers and style rendering the flower useless for hybridizing. They also eat large areas of the epidermis thus spoiling the appearance of the flower. They can be removed by pulling them out of the flowers with fine tweezers. Earwigs tend to congregate in large families so some chemicals may be necessary if the infestation is serious.

Hemerocallis gall midge (Contarinia quinquenotata)

This tiny white insect places its eggs into the newly formed daylily buds and the growing larvae feed from within the developing flower bud. The damage is manifested mainly in daylilies flowering during early midsummer; they show distorted and discolored tulip-shaped buds which usually start to rot before an actual flower is produced. If opened, small white insects can be seen with a hand lens or microscope. If this midge is suspected or if plants come to you from a garden that it has invaded, then it is advisable to place the plants in a quarantine area. They should remain there for a season with the basal areas dressed with Chlorophos, which should destroy the emerging pupae. Scapes with deformed buds should be cut off at the base and burned. Infestations are worse if there is an abundance of rain in late spring or early summer.

Hemerocallis thrips (Frankliniella hemerocallis)

This is the most common of the five species of thrips found on day lilies. At its worst it can cause shriveling and death of the undeveloped flower. Paler colored daylilies are most often attacked. A useful biological control is Orius insidious, a member of the stinkbug family. When all the thrips are devoured this control will then start on mites and other insects. In some climates Hemerocallis Thrips can over winter in the fan where the inner leaves join the crown.

Slugs and snails

These affect the leaves rather than the flowers, sheltering over winter in the foliage of evergreens and damaging the new soft shoots as they emerge in early spring. They congregate in the middle of mature clumps and are often only discovered when the clump is dug up for division. The populations can be kept down with careful garden hygiene, the use of chemical deterrents or natural predators.

Spider mite

Two-spotted spider mites (Tetranychus urticae), which are present wherever there is vegetation, suck the chlorophyll from the daylily foliage causing it to turn a dull brown and possibly die. This mite is much more of a problem in hot day climates and where plants are not watered thoroughly. The barely visible insects sometimes cover the leaf surface with a fine webbing. Treatment with a miticide may be necessary.

Tarnished plant bug (Lygus rugulipennis)

The oval adult bugs, which move very quickly, are mottled light green to coppery-brown and 5mm (1/4in) long. Their forewings have black-tipped, yellow triangles and from the side the body slants downward to the rear portion of the wings. Nymphs, which are yellow-green with five black dots on the body, look like adults but are wingless. Adults and nymphs pierce leaves and buds and suck plant juices; nymphs are the most damaging. The saliva is toxic and makes buds and pods drop and distorts leaves and shoots. Plants wilt or are stunted and branch tops blacken and die back. Natural predators are minute pirate bugs or damsel bugs when available. If necessary spray with Rotenone or Sabadilla. Spraying soap and oil in the nymph stage while the pest cannot fly is also effective.

Diseases

Bacterial soft rot

Often called crown rot, this results from damage to the roots or crown, possibly from nematodes, so that bacteria such as Pythium, Phytophthora, Rhizoctonia and Fusarium, present in many soils, can penetrate the plant tissue. The foliage, crown and roots are rapidly infected and the plant becomes a mushy, foul-smelling mess. It is difficult to cure once the infection has taken hold but treatment with Streptomycin may help. The rot usually attacks newly planted or freshly divided plants so it is a wise precaution to see that wounds are fully dry before replanting, allowing a new epidermis to form. The rot is also more likely to occur in high heat, humidity and very moist soil and is probably gene-related since it comes down through fairly narrow, but distinct breeding lines. It is far less of a problem in colder and cooler climates unless it has already taken hold of a plant received from a nursery in a hot climate.

Granular fungal rot

Not usually a problem in European gardens, Cercospora hemerocallis tends to attack daylilies that are under stress or possibly do not have genetic resistance to fungi. Starting with a yellow-streaked leaf, mature clumps can suddenly develop a layer of tiny, brownish black spore sacs. The fungus produces a white, thread-like network that quickly spreads over the crown and the leaves. At the first sign of it, dig up the plant and remove any affected parts, treating the portion remaining in a 10% solution of bleach and sterilize all the surrounding soil.

Leaf spot

This is caused by types of Botrytis or Colletotrichum which causes the leaves to turn yellow. Affected leaves should be removed and the daylily sprayed with a fungicide effective against downy mildew.

Leaf streak disease (Aureobasidium microstictum)

This is a fungal infection and widespread wherever daylilies are grown. It is often overlooked or attributed to leaf senescence or poor nutrition. It enters the leaf at a point of damage and is first seen as slightly darker green translucent spots which gradually become necrotic, then chlorotic and, finally radiate out as streaks allover the leaves. There are no controls but attention to garden hygiene and good cultivation, helps to make the daylilies more resistant.

Iris leaf spot (Mycosphaerella macrospora)

This fungus over winters on leaf debris and infects the new season's foliage growth. It becomes apparent first as brown lesions which develop grayish centers. These increase in size until the leaf withers. If unchecked, the vigor of the plant soon deteriorates. To combat this fungus, remove leaf debris at the beginning of winter and apply a copper fungicide spray when the new season's growth is 20-30cm (8-12in) high. Repeat dosage at fortnightly intervals is advisable.

Spring sickness

No one knows with any certainty what causes the problems collectively called 'spring sickness'. It can manifest itself as a twisted or pleated effect on the inner leaves. In a mild case, these may straighten and grow properly rather than turn brown and die, and scapes will appear during the current summer. But if the daylily is severely affected there will be no bloom scapes in the current year since the scape tips cannot push their way through the mushy, rotted leaves and the plant ceases to grow. Spring sickness usually occurs in regions in which there are several cycles of spring freeze/thaw conditions. A similar effect can be caused by insect larvae eating the new spring growth inside the crown rather than bacterial invasion. The new growth emerges light green with yellower edges that can be jagged, twisted or kinked.

Problems

Early-morning-opening

In colder regions, or temperate regions with a mild summer climate, daylilies with nocturnal ancestry seem to have a better chance of opening well early in the morning. Optimum performance is achieved in climates where there is an even night and day temperature, even if it is not necessarily a high temperature, although daylilies generally do best where the night temperatures are not less than 18°C (65°F). Some growers claim that the temperature on the previous three or four days and nights can affect the opening ability of a daylily flower.
Now that daylilies are increasing in popularity it is hoped that more breeders will take up the challenge of producing more cultivars carrying the early-morning-opening gene. The criterion for early-morning-opening is that the blooms should be open by 6am true solar time.

Petal boating

This is the term given to petals that have a folded or canoe-like appearance. It occurs after cool nights, especially in cultivars without early-morning opening genes, usually tetraploids of heavy substance with picotee or gold-wire edges and most often those with a prominent petal appearing, tongue-like, above the others petals in alignment.

Green sepals

These are sepal reverses that are still green when the flower opens. This is because the pigments have not matured fully, especially at the tip and is due to the bloom season coinciding with a succession of cold nights. 'Eenie Weenie' often has green sepal reverses, which are always more noticeable on paler flowers.

Scape blasting

The scapes appear to have spontaneously broken off horizontally or to have, quite literally, exploded. The blasting does not necessarily sever the head completely and it may continue to flower provided it is still attached by the cambium layer. Scape blasting is thought to be due to irregular moisture availability or over watering, or an excess of nitrogen, and is more prevalent in tetraploids although breeders are now aiming to eliminate this negative trait.

Scape cracking

This is vertical cracking or breaking of the scapes, often caused by overuse of unbalanced fertilizers. It can help to splint the scape with a stick if one is intending to use the bloom for the current year's breeding. It was a severe problem in early tetraploid daylilies.

Grassing

An overabundance of grass-like shoots growing closely together occurs in clumps of dormant daylilies that have been raised in a cold climate, trying to adapt to hot weather conditions (for example, many of the Siloams). The shoots need to be pulled apart and replanted separately. It is not the same as a soft crown, which can regenerate by producing little fans around the rotted crown.

Yellowing leaf tips

This condition can appear because the plant has split at the base due to expansion of the crown during frost damage, and is starting to discard the damaged leaves. If the yellowish-brown color on the tips starts to creep down the leaves and some of the leaves split, this could be caused by spider mites.

Yellowing of basal leaves

Yellowing or browning of the lower leaves may be the plant's natural response to unsuitable temperatures. These leaves should not be removed as they may provide a natural defense.

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