Daylily Pests and Diseases
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Pests and Diseases

One of the things that got me attracted to Daylilies besides the range of colours and shapes of the flowers is the fact that Daylilies seem to be free of pest and diseases. Now I say they seem to be free because so far the only thing I have encountered is Spring Sickness which I will discuss later. But Daylilies do have pests and diseases. You will find that if you only have one or two plants the chances of contracting something is much less than if you grew field of Daylilies. Its a general rule of thumb in gardening that the more plants of the same kind you grow the greater the possibility of a pest or disease becoming established in your area.

Factors like weather can increase or decrease the chances of an infestation. Cool, damp summers increase the likelihood of a disease while insects prefer warm, dry summers.

It is a good idea to have some knowledge of the common pests and diseases are so you can diagnose a problem should it arise. One of the traps some people may fall into is thinking that a sickly or weak looking plant has some form of disease when the problem may be more cultural in nature. Not enough sunlight will cause a plant to stay small and weak, probably it won't flower. Other possible culprits could be too much or too little moisture, fertilizer or lime in the soil. Incorrectly applied pesticides or over spray of herbicides. Extreme weather conditions such as drought, wind or hail can also cause damage to plants.

A good idea if you have the room is to make a quarantine area to move plants you suspect of being diseased. This will give you a chance to observe and treat the plant if necessary.

Pest Control

In the early to mid 1900's the most popular method of pest control was to have a heavy regime of chemical sprays and dusts. Gardeners would start their spraying in the early spring to catch the newly awakening insects that were dormant over the winter months. Sprays would continue all summer and into the fall. Then more people became aware that the sprays used were not only eliminating the harmful insects but also the beneficial insects as well. These pesticides were killing off the spiders, ladybugs, mantises and birds that will feed on the harmful insects. Many of the old chemicals were also carcinogenic. Nicotine is a prime example of this as for a long time nicotine was the primary component in many insecticides.

DDT (Dichloro-Diphenyl-trichloroethane) was one of the cure all chemicals used after World War II. After certain fish eating birds like the Osprey and Bald Eagles were found to have very weak eggs shell, the scientists traced the problem back to DDT being leached from the soils back into the water tables and eventually into the lakes and streams. This chemical pollution was absorbed by the fish stock and eventually eaten by the birds. Once this was discovered the use of DDT was banned in most places. This is an example of how we can effect the environment if pesticides are not developed that are biodegradable before they become a problem.

Finally as commercial growers and home gardeners became more aware of the dangers of using the old chemical pesticides, newer less environmentally costly methods were looked into. Suddenly the Organic gardeners were taken seriously and their methods which seem to work very well became crucial to the modern gardening literature. Their main premise is let nature take care of nature since it has being doing quite well for close to 3 billion years or more. Instead of spraying to control pests like aphids, collect ladybugs or spiders and place them close to the affected plants. You would be surprised how quickly they eliminate the problem and move on to the next area of infestation. Whole business have arisen what specialize is distributing live ladybugs or Preying Mantis egg sack so they can hatch in your garden. If sprays have to be used only organic solutions made primarily from non-toxic soaps, or diatomaceous earth, thuricides.

Thuricides: Bacteria based spray that is concentrated and full of tiny micro organisms that are lethal to some insects which eat them. When mixed with water, this bacteria will sit active on plant surfaces and be ingested by any foliage eating insect. Once inside the digestive system, the insect will stop eating after a few days and then die. This bacteria is harmless to mammals and other more sophisticated animals like birds and people.
Many will use systemic pesticides as usually one application per year is enough and does not have the same impact on the environment as repeated applications of chemicals.

I personally do not use any prays in my garden and encourage the beneficial insect to flourish. It is very interesting to see a spider or wasp doing what nature intended it to do. I would like to make a note that even though I have numerous bees and wasps of all different types in the garden I have so far not been ever stung by either one. Bees and wasps will leave you alone if you leave them alone.

Daylily Diseases

Bacterial Soft Rot

This disease also goes by the name of Crown Rot if you cannot find information under Soft Rot. As its name implies it is caused by a bacteria and not a virus or fungus. This bacteria is resent in many soils. The entire daylily can quickly become infected and turn into a putrid, bad smelling, mushy mess. The bacteria enters the plant through a wound or natural opening. High moisture levels can cause such rapid growth that the plant may die in a few days.

Your soils might not be affected by the bacteria but newly purchased plants that are infected might bring the problem to your garden. Inspect all plants before planting them. If you suspect a plant might have something wrong with it, place it in a quarantine bed to observe. If nothing happens after a few weeks, then move it into the garden. It is better to wait and be sure, than spreading the bacteria to your soil and adjacent plants. One way to way to prevent problems is to soak all new plants in a solution of 25% chlorine bleach to 75% water for 20 minutes then rinse off before planting. This does a good job of killing the bacteria.

If you suspect a plant of having soft rot, dig the plant up immediately and cut off the infected parts. Soak the rest of the plant in the bleach solution. I would treat any cut areas with Garden Sulphur to prevent re-infection. Do not plant back in the same place. Sterilize the soil before planting anything back in the same area you took the infected plant from. Information on soil sterilization can be found from Government Agriculture departments.

Leaf Streak

Leaf Streak (Aureubasidium microstictum) is a fairly widespread disease that is caused by a fungus. The fungus usually enters the leaf from a wound. It first shows as slightly darker green translucent spots, these gradually become necrotic, then chlorotic (pale, weak foliage). In the final stages the spots radiate out as streaks all over the leaf. The fungus while making the plant look sick does not really kill the plant, but the decrease in chlorophyll will weaken the plant over all. Best thing to do is remove the leaves and destroy them as they appear.

Mustard Seed Fungus

Mustard Seed Fungus (Sclerotium rolfsii) is found near the crown of the daylily. It shows up as a mass of white cottonlike sheets or threads. This is followed by small black or brown spores the size of mustard seeds on the leaves. Sometimes the leaves will turn completely yellow. To control the problem applying a fungicide as soon as it is noticed. Did up the plant and remove the immediate affected leaves. Soak the crown in the fungicide solution, replant in a different location. Sterilize the infected area soil before planting anything else the spot.

Spring Sickness

Spring sickness is one of those mystery problems that the cause is not really known. To recognize it the symptoms show as a twisted or pleated effect on the inner leaves, they will often grow sideways with a brown saw-toothed edge and holes. These can suddenly appear in the spring on healthy new leaves. In milder cases they may straighten and grow normal, flowering may occur that season. In severe cases the scapes cannot push their way through the affected leaves. Spring Sickness normally occurs in areas that have a number of freeze/thaw cycles. There may be a fungus involved but that has not been confirmed.

Daylily Pests


Aphids are a common pest in most gardens and daylilies are not immune to their spa sucking habits. The first sign to look out for is a yellowing of the leaves, buds and blooms may also become deformed. White flecks that look like dandruff but are actually the shed skins of the aphids are a sure sign of infestation. The leaves may show a clear sticky sweet secretion. This may attract ants as they seem to relish the secretion. The daylily aphid is bright green in colour and very tiny. Aphids can reproduce very quickly and spread through your garden in a short period of time.

To control them I would recommend using organic methods as opposed to a chemical pesticide. Ladybugs and their larvae are voracious devourers of aphids. Wolf spiders also do a good job of controlling them. If you have to spray an organic insecticidal soap is a good option.

Spider Mites

Spider Mites are very tiny mites that suck on the chlorophyll of the daylily plant, causing it to turn a light green or yellow colour. The point of injury can also cause a brown spot which may look like daylily rust. If you look under the leaves you may find webbing, this gives them the Spider in their name. You may also see the tiny mites moving in the webbing, a magnifying glass might be necessary. The mites usually feed on the underside of the leaves, this often leaves a dried silver to grey cast.

Spider Mites prefer a dry, hot summers. One way to slow them down is to mist the garden in the evening. Gardeners quite often just use jets of water to remove them off of the plants. In really heavy infestations a miticide might be necessary, but one thing to know is that if the wrong type of pesticide is used it could actually increase the mite damage. Spider mites can become immune to specific chemicals so rotating products is very important.


Slugs are not in actually insect, but they can become a pest in the garden if not controlled. They can feed on the dormant plants in the areas of mild winter and the newly emerging shoots in the spring. They usually feed at night and hide in the daytime. Organic mulches are perfect hiding places for the slug as they are cool and damp. Quite often a shiny slime trail is the only way to see slug evidence in the daytime. Slugs and their cousins snails are very soft underneath, because of this applying sand, rough gravel or diatomaceous earth around your plants will slice their underside and kill them. Apparently ducks find them good to eat, so raising a few in your yard might help as well. In very extreme cases slug pellets maybe necessary.

Tarnish Plant Bug

The tarnish plant bug feed on the flower buds and this may prevent the flower from opening up fully. The adults and nymphs pierce leaves and buds, then suck out the plant juices. The saliva is toxic resulting in buds and pods drop, distorted leaves and shoots. Plants can wilt or be stunted.

The insect is about a quarter of an inch long, the body is a mottling of several colours. They feed on a number of different plants in the garden and can produce 5 generations in one season. This makes it difficult to control. Natural predators are Pirate Bugs or Damsel Bugs. Spraying the nymph with a soap and oil solution is effective.


Thrips are one of the most common pest of daylilies, These small winged insects bore into the buds and suck out the liquid within. The wounds bleed and the liquid makes the petal stick together so the flower cannot open properly. Biological control using beneficial insect is the best way to control them. A member of the stink bug family do a very good job.

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