Pests and Diseases of Pond Plants


Pests and Diseases of Pond Plants

As a grower and supplier of a wide range of interesting, rare and unusual pond plants, I frequently get bombarded with questions about pests and diseases, so this article is a basic guide to some of the more frequent infestations and diseases and how to treat them, and I hope this helps with the battle to keep your ponds and plants disease free.

 Black Fly and White Fly

Both spread incredibly quick, with Black Fly giving birth to live young, whilst White fly laying eggs that grow into adulthood at a phenomenal rate. Black Fly seems to love Alismas and Water Lily leaves, but there are many other aquatic plants on the menu of choice too. Colocasia (Taro), and many other broad leaved plants unfortunately, attract White Fly. You can easily spot signs of these little monsters as affected leaves on the plants, will rapidly become yellow and sickly looking before decaying. I recommend that the best treatment to get rid of them, is to spray them with a good garden centre insecticide like Bug-Clear but  – WARNING – DO NOT SPRAY THIS PRODUCT IF THERE ARE FISH IN YOUR POND.White Fly


Spider Mite

Just visible to the naked eye, Spider Mite has a massively fast breeding rate and can quickly infest individual plants quickly spreading to larger areas. Signs of infestation to look out for include, dusty looking leaves that are turning brown, yellow or discoloured, and ultimately, silk webs that are heaving with movement. The best treatment is to spray the leaves, but there are many affective treatments available from most retail garden outlets. If you have Spider Mite, always remove any of the badly damaged leaves.Red_Spider_Mite[1]

Leaf Spots

Many plants can become infected, but this fungal infection often occurs particularly on Water Lily leaves. A good sign that you have Leaf Spot is to look for any brown unattractive spots that are dispersing across the Lily pads. My advice is that you simply remove all damaged leaves or cut back the entire growth which will produce new, fresh green fungal free leaves that should grow back quickly.

 Crown Rot

This is by far the biggest threat to any pond. Crown Rot is caused by a fungal infection that can spread fast and wipe out whole colonies of Water Lilies in a single body of water. Stressed plants are highly susceptible, so avoid pre-potted Water Lilies as they are often become or are already pot bound. Other triggers for stressed plants include a lack of sunlight, rapid change in water temperature and lack of nutrients. I would always be particularly aware of this when buying plants such as Nymphaea Chromatella, as it is highly partial to stress. The signs to look out for are healthy Water Lilies that suddenly go downhill, presenting yellow curly leaves. A simple test is to pull a stem gently and if it comes away from the crown with ease, it’s a good sign that it has Crown Rot.  WARNING – (NEVER BUY WATER LILIES WITH ANY SIGNS OF YELLOW OR YELLOWING LEAVES)

Unfortunately, there is no cure for infected plants other than immediate disposal of them, and I fully recommend that a thorough clean out of the pond is done a.s.a.p. Any remaining healthy looking Water Lilies should be removed, isolated and treated with a Systemic Fungicide, after which they should then be quarantined for a minimum of 6 weeks, before returning them to your pond.

 Snail Infestations

People love Water Snails and they play a valuable and important role in our wildlife ponds in maintaining a good eco-system.   Occasionally though, our single little helpers become an army and infestations can occur. Fortunately, the plant damage caused by their appetites is by no means a major threat and my advice is, to let wild birds and other Snail predators restore the balance naturally. If you are starting from fresh or have a new pond, I personally would recommend that you buy the less invasive and more diet conscious plant eaters such as Rams Horn Snails rather than Stagnalis Snails which breed much more quickly and will munch on your plants at a faster rate.

 Water Lily Beetle

These are strange little insects that infest our ponds in the summer and are quite partial to Water Lily leaves and will attack them with verocity.   The grubs look like motionless, black bird droppings with an orange under-belly. The Water Lily Beetle, properly known as (Galerocella Nymhacae, often can be seen laying their eggs near grubs and pupae. The Water Lily Beetle is more of a nuisance than a threat as they will munch away at the Water Lily leaves, stripping them down to a skeletal appearance or just leave them full of holes. However, the good news is, fish like to eat them so simply brush the grubs off into the water. You can also remove any damaged leaves or even cut back the entire growth leaving room for new, fresh green uninfested leaves to emerge which should grow quickly. You can also spray with Bug-Clear Insecticide, but as mentioned, it’s NOT recommended that you do so if you have fish in your pond. If you do have fish in your pond then I would suggest, that you remove any affected Water Lilies and place them in a holding tank, spraying them and leaving them for two or three days before returning them back to your pond. Always be sure to remove any and all of the dead grubs.Water Lily Beetle


Chinese Mark MothsChinese Mark Moth

These small moths like to lay their eggs under the floating leaves of aquatic plants. The larvae hatch and cut an oval segment in the leaf up to 1 inch in diameter, and then they knit two leaf segments together which cocoons them inside. Chinese Mark moths construct flat floating homes that free float around the pond and when their sheltered raft collides with a new leaf, they simply attach it with silk and get nibbling again. The damage to leaves can be rather extensive. The best cure is to net out any visible flat leaved larvae homes and cut back any infested plant growth. Again, there are insecticides that can be used, but most are damaging to fish and other wildlife so I would therefore, HIGHLY RECOMMEND NOT USING ANY.