pond plant pests

All plants can be affected by pests, parasites and disease at some time or another and your aquatic plants are no exception. However, most of them tend to cause problems to the appearance of the plant rather than causing you to lose the plant altogether.
There are obviously going to be restrictions on the way you use chemicals if there are fish in the pond as they will be seriously affected by these and fatalities will be high. Therefore, a biological approach is needed when treating any problems, and in some cases the fish can actualy help with this. Pests such as insects occur above the pond on the leaves of the plants but if you spray them with water they will fall into the pond where the fish will readily feast on them for you. If chemical treatment is needed it is best to remove the plant from situ, immerse it in a bucket of the diluted treatment for up to an hour, remove and rinse thoroughly, and then rinse some more, before returning to the pond.

As waterlilies are the most decorative pond plants, any pests or disease are usually quickly spotted as these plants receive the most attention and admiration. Problems usually occur with the leaves where insect larvae will bite, bore and tunnel causing, in some cases, severe disfigurement if not caught early enough. The most common offenders are greenfly and leafhoppers, both of these will suck the sap from young growth which is just above the water level. In lilies that are planted correctly, their leaves will lie on the surface and fish will often feed on these pests. However, in overgrown lilies their leaves are held above the water where the fish cannot reach and infestation can become severe, this will cause the leaves to go brown and eventually die.
The larval stages of some beetles, midges, moths and flies can cause problems that although are less common, can prove to be more disfiguring.
Caddis fly larvae swim around the pond in protective cases that they make for their bodies out of leaves, sticks, pieces of shell and sand. They feed on young waterlily leaves and will completely destroy them in severe attacks. It is not possible to treat them with chemicals and you are dependent on their natural enemies ie. the fish, doing the job for you.
Body protection is also used by the caterpillars of a small moth which is often seen over the water at dusk. When the caterpillars hatch they will shred leaves to form body cases and then proceed to eat the lily leaves, they often make large holes and in extreme cases can skeletonise a leaf completely.
The larvae of the leaf-mining midge can cause the greatest disfigurement as when hatched from their eggs, which are laid on the leaf surface, they will burrow into it and eat, causing raised channels in the outer layers.
The most destructive pests are the waterlily beetle grubs. Although only 6mm long it makes up for it's size by laying clusters of eggs on the leaves in summer, which hatch into tiny black larvae with yellow undersides. These cause devastation on the plants as they eat away the tissue between the veins. The larvae will pupate on leaves above the water in autumn so any aerial foliage should be removed, and also as this is a sign the lily is overgrown, steps should be taken to remedy this.