Aquatic Plant Pests
As with other parts of the garden, the pond and its surroundings can suffer from a variety of pests. In the main these are insects, which are very difficult to control with traditional insecticides as these can both kill the fish, and seriously disrupt the ecology of the pond. The best remedy for insect pests that are in the water are fish, which delight in devouring all manner of aquatic insect life. Pests that cling to the aerial parts of the plants should be knocked into the pond using a strong jet of clean water, the fish then being permitted to clear them up.
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 The best remedy for most troublesome aquatic insect life is a healthy stock of fish.
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 Waterlily aphids can be controlled by spraying their over-wintering hosts with a winter wash.
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Fortunately with the most serious pest of aquatic plants, the Waterlily Aphid, there is an alternative remedy, although when aphids appear on plants during the summer months, the only respite that can be obtained from its attacks is constantly knocking it into the water with a jet of clear water. Fortunately during the winter it rests as eggs in the fissures of bark on plum and cherry (Prunus) trees where it can be sprayed with a winter wash. This breaks the life-cycle.
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Caddisflies spend most of their time in the water. At least the troublesome part of their life from the gardener’s point of view. These tiny creatures in their juvenile stage make little shelters for themselves from pond debris. With some species a portion of this is plant foliage which they shred from aquatics with floating foliage of plants like waterlilies. Usually this is merely disfiguring and often a mystery to the water gardener who has not observed the pest.
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 Caddisfly larvae often remove pieces of foliage from plants to help make their protective shelters.
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However, the torn foliage may then become infected with a fungus and start to deteriorate further. A balanced fish population will generally keep the caddisfly population within bounds.
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 The most troublesome pests are aquatic snails. They can cause severe damage to foliage.
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The worst pest for devouring leaves are water snails. Many species reproduce rapidly and if they are not controlled can cause serious damage to the flowers and foliage of all deep water aquatics. A number of aquatic snails will devour algae, but the majority are troublesome to some degree. A balanced population of fish will help to control them as they feed upon their eggs, and also tiny immature snails, but they are not helpful at the time that the plants are being damaged.
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The only method of control is hand-picking, this being aided by the addition of fresh lettuce leaves floated on the surface of the water overnight. The snails gather beneath these and can then be removed and destroyed.
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Caterpillars are generally less troublesome, but can cause serious damage to emergent foliage. When they attack bog garden plants they can be controlled with a contact insecticide, providing that this is kept well away from the water. With marginal aquatics it is a more difficult proposition, for insecticides can cause serious problems for fish and the pond ecosystem. Hand-picking is the only remedy, badly damaged foliage being removed as a matter of routine.
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 Caterpillars can cause severe damage to the emergent foliage of plants like Nelumbo.
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