Aquatic Plant Pests

Much more of a nuisance are the pests which attack the leaves and tubers of water-lilies. Among these can be included: aphids, especially the reddish-black one, the Water-lily Aphis, Rhopalosiphum nymphaeae; the larva of Caddis flies, Trichoplera, and of the Brown China Marks Moth, Nymphula nymphaeala. Aphids lay their eggs on the leaves of water-lilies and the larvae feed off the leaves. The China Marks Moths lay their eggs near the edge of leaves or underneath them and the larvae are quite capable of destroying the foliage. The larvae of the Caddis fly, in its protective suit of armour, crawls about the bottom of the pond and can sometimes damage the tubers of water-lilies and their buds. To say as much about these pests is to conjure up a picture of a pond ravaged and denuded. The extent of the problem is very much a matter of luck. These insects may be quite rare in one area and quite common in another. But the remedies are both simple and effective. The most important one is fish; have your pond well-stocked with young, vigorous goldfish and Golden Orfe, and they will feed readily off these insects and their larvae. The leaves of water-lilies often rise well clear of the surface and the upper portion of all floating leaves will, of course, be out of the reach of the fish. So you can aid the fish in two ways. Spraying the leaves with a firm jet of water is one way: the insects are forced into the water. The other is to spread a net over the lily leaves and submerge them by holding down the net with weights. Placing plants in a bath of Derris is sometimes recommended. But the cure may prove worse than the pests. Derris is highly toxic to fish and unless all traces of the insecticide are washed off the plants before returning them to the pond, you may find yourself minus your fish stock. 1 would use such a measure only in the most extreme of cases. Where aphids are a particular problem, cut back the dead foliage of marginals hard and burn it. The adult insects hibernate in the hollow stems of waterside plants. Finally, the Freshwater Snail, Umnaeastagnalis, will often develop a taste for leaves and sometimes buds. However, given the choice, this snail prefers the head of a lettuce or a cabbage stump to water-lilies. Place one or two of these plants in the water on a few successive nights and simply remove the snails attached to them. Surplus snails are quickly eradicated in this way.

As regards floating plants — the Water Soldier and Frogbit in particular — pond owners are sometimes baffled by the fact that they had a plentiful supply in one season only to find that they have none in the next. What had happened? It is possible that the plants simply rotted away at the end of the summer. But the owner’s own conscientiousness may have been his undoing. The Frogbit spends the winter months as small, insignificant buds resting on or immersed in the mud on the bottom of the pool. Similarly, the Water Soldier may only survive the winter in the form of little bulblets which grew and separated from the mature plant in summer. In cleaning out a pond in autumn one can un-wittingly throw out these plants. It is not a bad idea to collect them before they sink to the bottom and transfer them to a jar of water. The same can be done with the seeds of Trapa natans, the Water Chestnut (but it will hardly ever set seed in the British Isles or Ireland).

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