Water Garden Pests and Water Lily Diseases

Published on July 25, 2009


Unlike most specimens of the plant kingdom, pests or diseases seldom afflict water lilies. Water gardeners have it easy compared to gardeners who grow roses, veggies, or lawns. Plus, most water lily troubles are superficial and do little permanent harm. Often they may be prevented and controlled with a watchful eye and careful maintenance.

Here are the most common, from big to small. Some may not be a problem at water garden businesses, but might affect your customers. Remember that the key to keep pests from becoming problematic is to regularly monitor the condition of all your aquatics. Then before anything can become a concern, you can nip it in the bud.

Terrestrial Animals

Dogs don’t eat water lilies. However canines cause problems when they go for a dip, blissfully overturning pots. While some dogs can be trained to stay out of the pond, breeds like Labradors have an innate love for water. In those cases some owners solve the problem by giving their lab its own kiddie pool. A harsher solution is the Fido Shock, which delivers a small electrical charge through a wire fence.

The electrical fence can also deter raccoons, who regularly knock over aquatic plant containers. Keep pots away from the pond edges since the raccoons won’t go into deeper water. These critters are very persistent and outwit most devices designed to scare them away. The most effective deterrents are the Fido Shock and the Scarecrow, a sprinkler activated by motion sensor. Move the Scarecrow periodically to increase effectiveness. It also helps to place two at right angles. If deterrents don’t work, check with your animal control departments. Often they’ll provide traps then remove the captured animal. To bait the trap use the unlikely, but extremely successful, delicacy – Twinkies.

Aquatic Fauna

Turtles will eat anything slower than they are and that includes water lilies. Symptoms are lily pads that appear to have been cut with a knife or scissors. The best solution is to relocate the turtle to a more appropriate pond.

Some koi will snack on lilies and root around in pots while others don’t. Until someone figures out why this happens, take precautions to reduce koi damage. Cover the soil in containers with gravel and then with stones–bigger than the largest koi’s mouth. (Some ponders say lava rock is uncomfortable in a koi’s mouth and they’ll avoid it.) Place lilies very close to the surface (3-6?). This prevents koi from grazing in the pot and also gives new leaves a chance to grow.

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Butterfly koi usually make better water garden pondmates, as do goldfish and koi raised from babies. Whatever you do, don’t add a single pot of plants into a pond that has been sterile of vegetation. The new diversion will soon become lily salad. Another strategy to protect water lilies is to buy or make a cage around the plants. As a last resort, create an adjacent but separate pond area for the lilies.

Ramshorn and Japanese Trapdoor snails don’t usually harm aquatics since they feed on decaying plant material. However Pond and Apple Snails do feast upon lily pads and other fresh vegetation. A technique to get rid of snails without altering your water chemistry is to place a lettuce leaf or zucchini slice in the pond. Leave it overnight, then remove it and destroy the snails it has attracted. Repeat as needed. Adding snail-eating fish, like the Clown Loach, is another biological control. Potassium permanganate and other specialized chemicals can be used but the biological controls work best in backyard ponds.




The key to controlling aphids is to keep them from ever becoming a problem. As soon as you notice the little buggers, squash them by hand. They usually appear on new growth or older yellowing leaves and may start reproducing in terrestrial plants near the ponds. Although many books recommend washing aphids off leaves so the fish can eat them, this only works for light infestations. You can overflow the pond, spraying hard to flood them out. Repeat every day or two until aphids are under control.

Light oil sprays will suffocate the aphids and are not harmful to fish or plants. Sprays should be repeated every 10 days to be most effective. Mix two parts vegetable oil to eight parts water and a dash of dishwashing detergent. Treat in the evening and rinse off the oil the next morning. A Volck oil spray (5 Tbsp to 1 gal water) also works. Spraying trees and vegetation around the pond as soon as any aphids are detected is the quickest way to prevent an infestation in the pond.

Other environmentally safe controls are available. Diatomaceous earth is a microscopic abrasive that kills the aphids. It can be dusted on the leaves or mixed with water and sprayed. Again, flush the pond of extra residue so it doesn’t harm other pond inhabitants. Blade Runner, Aphid-X, and Herbal Aphid Spray are all made from natural ingredients. A weak solution (1.5%) of insecticidal soap left on for less than an hour also works well.

A very low-tech aphid control strategy is to drown the aphids. This can be done by submerging the plants overnight or by putting some newspaper on top of the leaves and leaving it there for several hours.


Leaf mining midges chew wavy lines in the lily pads. These very small larvae can be handpicked, the leaves can be removed, or the water can be treated with Mosquito Dunks (which contain Bt).

China Mark Moth


This small nondescript brown moth is the water lily’s major pest and is also called the Sandwich Man. It is nocturnal and lays eggs on the underside of floating leaves. After hatching, the larva cuts leaf pieces to make protective sandwiches. They affect water lilies, although the larva also burrows into any floating leaves or debris. They have a two week cycle, so keep a close check for them throughout the growing season.

The mechanical control method, better known as squishing, works well to control an initial outbreak – fish just love the worms. Bacillus thuringiensis (Bt), a natural bacteria, can be used as a spray. Once ingested, it kills the larva but won’t hurt people, pets, or fish. It is the active ingredient in Dipel, Insecticidal Soaps, and Thuricide. As with many sprays, it is best applied at the end of the day (see sidebar). If there is a severe infestation, the best remedy is to remove all affected foliage close to the crown of the plant and destroy it.


Many years ago several varieties of hardy lilies were susceptible to crown rot, a fungal disease. The leaves on affected plants would curl and turn yellow, and buds would rot below the surface. The plant would soon die since the rhizome had rotten away, leaving a stinky mess. Treatment was to thoroughly soak the tuber in a fungicide. However, since the disease is highly contagious the best option was to remove the plant and completely destroy it. Luckily the incidence of this and other fungal diseases has decreased as less susceptible hybrids have been developed.

Natural or Chemical Treatments


Be cautious of all pesticides and always use the least harmful treatment first. If mechanical control (aka squishing by hand) doesn’t work, then try the appropriate insecticidal soaps, sprays, or dusts. These rely upon natural bacteria that target specific organisms, diatomaceous earth, or other natural derivatives. Unlike pesticides, they are usually not harmful to other insects and pond inhabitants. (Unfortunately those based on pyrethrum and rotenone are toxic to frogs and fish.) Numerous environmentally friendly treatments are now available, such as Blade Runner, Herbal Aphid Spray, Dipel, and several Insecticidal Soaps.

If biological controls are unsuccessful and you must resort to a pesticide, follow some simple precautions. Check what the label says about use with fish, pets, and other wildlife. Many products may be safe on terrestrial plants but should never be used in or around the pond. Whenever possible, remove the plant and treat it outside of the pond. After it has been treated, rinse it off and return it to the water garden. Some chemicals might require water changes after treatment if applied in the pond.

Most pesticides and biological controls are best applied at the end of the day. There is less breeze to blow spray to surrounding areas or plants; there is less chance the spray will burn or damage the plant; there is less opportunity for UV to degrade the effective ingredients; and absorption of the active ingredients into the plant’s system is usually higher.

An Ounce of Prevention Provides a Big ROI

• Before adding any new plants to your pond, closely examine them for signs of pests, especially if you’ve had infestations from a particular grower. Look at both sides of the leaves and in the crevices where stems and leaves overlap. Remove anything suspicious. You can also soak the plant to kill unwanted pests and parasites. Plants can be soaked in a potassium permanganate solution (4-6 Tbsp in 12-13 gal water) for 1-2 hours.

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  • Regularly fertilize plants and divide them when overcrowded. Since insects and diseases attack sickly and stressed plants, thriving plants usually do not have pests.

• Trim off all old and damaged foliage from lilies and marginals. This weaker growth is often where insects thrive. Removing dying leaves eliminates their food source, helps rejuvenate the plant, and reduces material that falls on the bottom to decay. A carefully trimmed lily displays beautifully and sells quickly, plus it’s usually disease and pest-free.

• When adding water to your ponds, be sure to spray all the plant foliage, especially if it hasn’t rained lately. This cleans the plants plus washes off pests before they can become a problem.

(Okay you should know what ROI means but just in case – Return on Investment)

37 thoughts on “Water Garden Pests and Water Lily Diseases”

  1. Please can you help my water lily leaves are covered in tiny holes almost lace like. What is the cause and how do I get my water lily back to good health. Thankyou

    1. Can anyone tell me what type of animal would uproot large water lily plants in a pond in Florida? The tubers of the water lily showed their white roots to be severed or broken 4 inches into the soil. The entire cluster were comprised of three different groups were found floating at the end of our pond.

      1. Avatar photo
        Lora Lee Gelles

        Hi John.
        Here’s a response for you from the author of the article, Paula Biles:

        It sounds like you have a large natural pond with the lilies planted into the bottom of the bottom soil. It’s not a liner pond with lilies planted in pots.

        Up north they may have problems like you describe, where the entire plant is cut off by the roots. It is usually caused by muskrats. A quick google search shows there are some in Florida, too.

        One other varmint may also be the culprit. I live in SW Florida but have only heard of a similar problem twice in the past 20 years. It was caused by an otter, which came into their ponds from a nearby stream. Both of them also had fish in their ponds. One homeowner took severe measures to stop the problem. I don’t know what the other one did.

        I just thought of one other possible, but unlikely, culprit.
        I have a 5′ diameter pond built in 1988. It is a plant pond without any pumps or filters, so it has up a nice deep layer of debris at the bottom. A few years ago Australian lily tubers were planted into that layer to establish a natural looking planting. My neighbor’s new dog loved to frolic in the water. After 2 of his visits the lilies all came floating to the top, dislodged from the bottom. I can’t imaging this happening in your large pond, but in a smaller pond an active water dog might be the animal.

  2. I am checking to see if anyone can tell me what to do about a worm that is getting on my lily pad flower petals both orange and white alike and eating small round holes in them?

    1. Jason, thank you for providing details about the worm and a description of the holes. • The easiest and cheapest thing to do is to pick off the worm and squish it. Use a tweezers or pliers so you don’t have to touch it. • A spray containing BT should also work since the leaves are being eaten. Spray it in the early evening since it is UV sensitive.

  3. Every September my nymphaea miami’s rose get their leaf stems abnormally long and leaves begin to curl and become increasingly red as the time goes by. Then after one or two months, all the plants are twisted and the leafs are turned upside down. After that mess, they have an ugly look for a few months, then at the end of March they turn back to normal. I try eliminating all the plants having that problem but nothing seems to work, and every year in different ponds and conditions they have exactly the same problem. Anybody know something about this?

  4. Avatar photo

    Thanks for writing. To solve your mystery, more information is necessary:
    1) What State and zone are you in?
    2) How long is your typical growing season?
    3) Can you send photos of the misshapen plants?
    4) What size pot(s) are they planted in? Does the pot have any holes?
    5) How long have they been in the pot(s)?
    6) When was the last time you fertilized them?
    7) Do you have other tropical lilies and are they growing normally?

    Aquatically Yours,
    Paula Biles

    1. 1) What State and zone are you in? 11 miami fl
      2) How long is your typical growing season? they slow down in winter but they keep growing
      3) Can you send photos of the misshapen plants? yes, where should i send them to?
      4) What size pot(s) are they planted in? Does the pot have any holes? 1.5 gal container with holes
      5) How long have they been in the pot(s)? all the season
      6) When was the last time you fertilized them? I fertilize them once a month.
      7) Do you have other tropical lilies and are they growing normally? yes i have some islamizada growing perfectly fine

    2. Hi guys,
      I am from Malaysia. I grow my lotus plant in a huge round pot of diameter – 50cm x 75cm height with guppie fishes in it. Got a lot of tiny snails.

      Recently, every morning a layer of oil was seen on the surface and some of the fishes perished. I cleared the oil floating and all remains normal until the same thing happens the next morning.

      Please advise the cause and remedy if any.

      Thank you,


      1. Hi Romacs,
        This is a new problem that I never heard before.

        When a land creature dies in a pond it can generate oil as it decomposes. However that does not seem to be the problem for you because you would see the dead creature and also smell a bad odor. And since your pot is 75cm above ground, a critter would not have fallen in.

        The only other possibility I can think of involves mosquitoes. Most neighbors and government agencies know that mosquitoes breed in water. So when they see a pond or water garden container filled with water, they believe it is causing more mosquitoes and get upset about it. The common way to treat containers with water is to add or spray oil on the surface. This suffocates the mosquito larva … and it also kills the small fish, like your guppies.

        In many residential areas in the United States, people with ponds talk with all their neighbors to teach them that all fish love mosquito larva … they are a fish delicacy. So bodies of water with fish will help reduce the neighborhood mosquito population. Plus dragonflies (also called mosquito hawks) like ponds and lay their eggs in them.

        Here in Florida where I live, many Mosquito Control Departments give out free gambusia (guppies) for people to put in their ponds and water gardens. They know it is the best way to control mosquitoes — it is natural, effective and long lasting.

        So you may want to check with your neighbors to see if they are adding oil to your lotus pot.

        Terima kasih. Semoga berjaya.


    1. Hi Caroline.
      To answer your question we need more information:
      1) What State and zone are you in?
      2) Do you know the name of the lily or if it is a tropical or hardy?
      3) What size pot is it in and how long has it been in it?
      4) When was the last time you fertilized it?
      5) Did it have any regular leaves earlier this year and are they normal size?

      Aquatically Yours,
      Paula Biles

  5. Betty Campbell

    Using BT is not a good choice. What does it do?? It kills catapillars… All catapillars, folks. There goes the butterflies and moths…major reason we are losing monarchs, Luna’s, Polyphemus, etc…don’t do it !!

    1. Prevention, hand removal, and non-chemical options are ALWAYS preferred. But when necessary BT (a naturally occurring microbe found in soil) can be a very effective treatment. Each BT strain is very specialized and only is active after being ingested by a particular larva — either a mosquito larva or a caterpillar. And the local application of BT on lily pads is broken down by UV within days. So the ONLY caterpillars it kills are the ones eating lily pads within a week or so of being treated. • Large scale treatment of countless acres of agricultural crops and incorporating insecticides into their genes is different and a huge problem.

  6. My newborn lotus leaves are turning blue then black. Please give me any help. Thanks in advance.

    1. Avatar photo
      Lora Lee Gelles

      From Paula Biles:
      So sorry to hear about the problems with your lotus leaves.
      To figure out what’s causing your problem ‘Sherlock’ needs a lot more info and a few photos if you have them.

      1) Are these the first new leaves that float on the surface?
      2) How big are the leaves?
      3) Where are you and what is your climate zone?
      4) Is your lotus in the pond or in a container on the patio?
      5a) Are the lotus in a pot that grew and bloomed last year? or
      5b) Or did you plant new tubers this spring?
      6) Do you know the name of your lotus variety?
      7) How deep is it from the top of the soil to the water level?

  7. I had rhizomes of two hardy water lilies. My new home has less sun, but currently the temperatures here is above 40 Celcius. Full day of bright light but direct sun only for 2 hrs. Both started rotting. I uprooted them and tried to float them in water, One of the tuber, just sank at the bottom and the other after floating for 2-3 days, sank. Now what should I guess from that. Are floating rhizomes alive or the ones which sink to the bottom? If they are alive, should I donate them to someone, because of less sun? Its very very hot here in Northern part of India.

  8. My potted water lilies have been eaten to the crown by my naughty gold fish. I’ve since removed the pot and put it in its own large water bowl without any fish. Is the plant likely to grow back?

    1. Avatar photo
      Lora Lee Gelles

      Hmmm … goldfish don’t usually eat lilies so your naughty culprit is probably something else. Goldfish will gulp down lots of duckweed and other small floating plants. They have also been known to nibble on delicate slow-growing plants in aquariums. However in water gardens they are regularly used as the fish of choice. At their worst they may occasionally dislodge small plants from the soil with their vacuum cleaner style of eating. But the plants just float to the surface.

      The lily may grow back if the culprit ate only the new leaves. Within a week or two you should see some new green shoots coming out. However, if the culprit damaged the growing tip then your chances aren’t very good for it to grow back.

      There are a few options for what ate the lily.
      • If your goldfish has small barbs (whiskers) on the side of its mouth, it is a koi. They DO eat lilies.
      • If you have snails in your pond, some varieties eat plants and love tasty new shoots. You could do a test overnight by floating a piece of lettuce or slice of squash. Look in the morning to see if it has lots of snails on it. If it does you may have found your culprit.

      Good luck and I hope your lily starts growing again.

      Paula Biles

  9. Our water lilies are developing brown spots with yellow edges. We didn’t notice them until I added some pond and fountain cleaner which came as a white powder. The local store said it shouldn’t hurt the fish so I thought it would be ok for plants. Please help!

    1. 1) Gently but thoroughly spray the surfaces of all your plants, especially the lily leaves.
      2) Find out the contents of the cleaner and ask the store about its affect on plants.(Many cleaners kill plants since algae is a plant and algae is what the cleaners get rid of.)
      3) If the cleaner is OK with plants, then be very careful when applying it next time. Teeny amounts of chemicals can travel long distances and do damage then they land on nice flat surfaces like lily pads.
      4) Check to see if the new leaves are also affected. If they’re healthy, then trim off the older leaves with holes so your pond can look as good as new.

      Good luck.

  10. I have 2 tropical water lilies that have been in my pond for about a month. They sent out leaves well within a week or so but the leaves have remained short (only a few inches), only about 4-5 inches in diameter at most and none have ventured toward the surface. The pond depth is about 18 inches and the top of the tubers is about 6 inches from the floor. They get full direct sun about 5 hours a day and off and on sun the rest of the day. I live in Far Northern California and our summer temperatures are rarely below 90 degrees during the day(more often about 95) and at least upper 60s…usually in the mid 70s at night. I have 2 hardy lilies also in the pond that went in about 6 weeks earlier that are doing well and have plenty of leaves at the surface. They have bloomed several times, but the flower color was advertised as deep red/purple and turned out to be white, which is why I ordered these. The variety is King of the Blues. I am in Zone 9b. Pot size is 10 inch. It was fertilized for the first time in the last 2 weeks

  11. Hello, I need help for my water lily. Recently lily got China mark moth. Why I get that insect and how to prevent not to get next time? From Singapore.
    Thank you.

  12. I have two small rain barrel lilies ponds, one gets sun most of the day the other half the day morning only. The garden toads visit both at night, one has an algae issue the other doesn’t, and the one with the algae the lilies are rotting. Both are treated the same. :;-( , _(“)_Namaste

  13. By viviparous propagation of water lily, I successfully planted an Egyptian lily in a bucket and suspended it in a well with a strong rope 2 ft deep, the inner part of the well receives moderate sunshine. Will it grow there and how long will take it to bloom?

  14. Waterlilies need 2 things to grow well and bloom: warmth and sunlight. Tropical lilies (especially young viviparous plants) need LOTS of sunlight. They are usually planted very close to the pond’s water surface (3-6″) to get the most sun and warmth.

    The best thing you can do for your little lily is to move it from the well to a decorative container at ground level. For the first several days you may want to cover it with shade cloth so it doesn’t get sunburned. After that it will be very happy to be in the sun … just like it would be in a natural pond.

    You may also want to add some mosquito fish (to eat mosquitoes) and submerged aquatic plants (to keep the water clear). If the growing conditions are good, then it may bloom this season. The size of your container should be at least 12″ across.

    Good luck.

  15. Hi Im in Australia and my lotus plants leaves are developing black spots with yellow rings and dying. Is this black spot? What treatment would you recommend?

  16. Sorry but I have never heard of Lotus Skin Disease. You and your sister can probably find some information by doing a google search. Good luck..

  17. There are a few kinds of aphids that can be pests on aquatic plants. However they won’t be any problem for your tadpoles.
    Some water gardeners spray the aphids off their plants into the pond as a tasty little snack for their fish.

  18. Just wanted to thank you for the newspaper trick for smothering aphids on water lilies. I did it in the evening (so the lilies weren’t missing out on sun light) and left the newspaper for about 3 hours. It was so easy to do and totally worked!!

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