Water gardens like all gardens; suffer from the attentions of plant eating insects and other pests. Although the closed nature of the pond environment imposes its own constraints on dealing with them, following a few simple guidelines, coupled with the judicious use of a few suitable products should ensure that any problems are fairly easily dealt with.
Water Lily Pests
Water lilies seem to be particularly prone to a variety of specialist insect foes – so if your water garden includes any of these most spectacular of water plants, it is probably a good idea to be on the alert. Water Lily Aphids (Rhopalosiphum nymphaeae), for example – small, black aphids which lurk on the lily leaves themselves, sucking their sap – can be a major scourge, especially for the well stocked pond and their attentions can seriously interfere with flowering and cause stunted growth. Controlling them involves a year-round regime, spraying nearby trees and vegetation with a suitable ovicide in the winter to destroy aphid eggs and periodically flushing the adults off the leaves and into the water with a hose to allow the fish or other pond life to eat them.
Aphids also have other natural enemies outside the pond including ladybirds, lacewing larvae, hoverflies and some kinds of parasitic wasps, so encouraging them to visit will help keep the aphids under control. Planting milfoil in the garden is said to attract ladybirds and growing yellow flowers, particularly marigolds, will tend to draw in hoverflies, while some gardeners have found that alliums – a group which includes chives, garlic and onion – can also help keep aphids away.
The water lily leaf beetle (Galerucella nymphaeae) – a small, dark brownish/black beetle and its tiny black larvae – causes unsightly disfigurement to water lily leaves. An infestation is difficult to treat with insecticides, so again using a hose to knock adults and larvae into the water is probably the best solution during the growing season, followed by tidying up vegetation around the pond later in the year to deny them an over-wintering refuge. Growing pyrethrum – a plant which emits a natural insecticide from its leaves – alongside the pond may also help with these and any other insect pests, with the advantage that it is a natural method of control.
Not all water lily problems are caused by pests, however. The appearance of dark patches on the surface of leaves, or a sudden blackening of pads and flower stems, accompanied by a foul smell from the root are more likely to be caused by water lily leaf spot and crown rot respectively. If so, the only solution is to ruthlessly eradicate and destroy the affected specimens.
For most other plants, the greatest threat comes – like their terrestrial cousins – from water snails, with foliage being eaten away and jelly-like egg masses appearing on the leaves. In addition to eating our prized pond plants, snails can act as intermediate hosts to a large number of pathogens and parasites, which can infect fish. The main culprit is the greater pond snail (Lymnaea stagnalis) – and slug pellets are not going to solve this particular problem! Their numbers are best controlled by the admittedly slow and tedious approach of removing them whenever they are noticed – or by using a suitable lure, such as floating lettuce leaves to attract the snails and then simply removing them once the creatures have covered them.
The water garden is really no different from any other kind of garden; wherever plants grow there will always be an army of insects and other pest ready to feast on the abundant foliage. The pond-keeper, however, is denied the usual option of using insecticides and other similar products to wage full-scale chemical war on the pests, since the self-contained – and relatively small – eco-system of the pond makes this largely impossible. However, there is scope for the use of some insecticides – chiefly away from the pond itself – to deal with the problem, which, coupled with a few more natural approaches, should enable the most voracious pest to be brought under control.