Water Garden Pests

The pool has been made and filled: the plants set in their allotted places. After a few weeks to give the oxygenators time to get established, the shining goldfish and mottled shubunkins slide from the oxygen-filled polythene travelling bag into their new home. The fountain splashes and the waterfall gurgles. The pool is finished and now there is nothing to do but sit back and admire it.

Or so the supplier’s catalogue seems to imply. In fact, of course, it is not quite as simple as that. Making and stocking the pool is only the beginning, the first step in a gardening adventure that will bring endless pleasure – and not a few surprises. The surprises are mostly pleasant, but sometimes make the beginner wonder whether all is going as it should. He becomes conscious of unfamiliar phenomena and he isn’t sure whether they are good or bad. Most of the puzzles are connected with the varied life forms that arrive from heaven-knows-where and settle happily in the pool as if it had been put there just for their benefit. Some of these uninvited guests – such as frogs, for example – are easily recognised, but many are totally unfamiliar.

The puzzle for the pond owner is first, what are they; then, are they a good thing; and finally, if they are not a good thing, how do I get rid of them? To me these eager colonisers of the pool are one of the bonuses that make the water garden a place of endless fascination and I am pleased to be able to say that most of them represent no danger at all to plants or fish (or people!) and they can quite safely be left in busy occupation of their particular niche in the complex ecology of the pool.

Within a very short time of completion the pool will be supporting an astonishing variety of insect life. Some, like the dragonflies, are beautiful; some are curious and some grotesque. None need cause a human being the slightest alarm and all, without exception, are absorbingly interesting in the details of their life and habits. And one or two are a nuisance.

There is a midge, for example, that lays its eggs on the leaves of water lilies. They hatch into very slender transparent wrigglers that are hardly visible to the naked eye. But the results of their labours can be seen plainly enough as they burrow through the leaf tissues, generally working from the edges inwards and eventually leaving a mere skeleton of ribs. A heavy infestation can cripple or even kill a young lily that is still struggling to get established and I am convinced that failure with the miniature Nymphaea pygmaea helvola is more often due to this cause than any other. The stronger growing lilies with thick tough leaves are hardly ever troubled; it is the smaller varieties like Froebeli, Aurora and the miniatures that are likely to be affected, and of these the mottled-leaved varieties seem to be the most favoured by the egg-laying insect.

A close watch should be kept on such varieties in the middle of the summer, and any affected leaves nipped off and destroyed. If the trouble continues, take up the plant and immerse it for an hour in a bucket of derris solution, then rinse it well in clean water to remove all trace of derris, which is highly poisonous to fish, before replanting. Where this trouble is persistent I have noticed that there is often a shallow stagnant ditch somewhere in the vicinity, evidently the midge breeding ground, because if this is completely drained, or filled in, the nuisance is immediately abated. Most garden pools are troubled only occasionally by this pest and many not at all.

A different kind of midge lays eggs which hatch into red larvae about £ in. long which travel in the water with a violent looping motion. They often turn up in water-butts as well as pools and are called blood worms. They have a bad reputation for invading the root tubers of water lilies with crippling effect but I am not altogether convinced about this. They are designed to live primarily on decaying plant remains – really soft broken-down stuff – and they are just not equipped for chewing healthy plant tissue. I suspect that the lilies they infest are already dying for a quite different reason and the blood worms simply move in to assist in the processes of decay begun by other agencies. But in this I am at odds with other authorities, so if any signs of infestation are seen it may be wise to mix up some more derris solution and treat the lily as recommended for the leaf-boring midge larvae, remembering to rinse the plant clean before restoring it to the pool. A derris insecticide can be obtained from your local garden shop and the solution should be made up as directed on the label.

There is nothing that can be done to prevent these midges, not to mention gnats and mosquitos, from laying their eggs in the pool, but very few of the eggs or larvae have any chance of surviving if there are fish present, which is a very good reason for always having a few fish at least. Unfortunately goldfish and shubunkins are inclined to get fat and lazy with age, and not bother with such trifles, but no insect or larva will stand any chance at all if there are a few small golden orfe on patrol. They miss nothing on or near the surface.

Another highly insectivorous fish is that pugnacious little native of our ponds and streams, the stickleback. Some say that it should never be introduced into ornamental pools because it will pursue, attack and wound other kinds offish. Frankly I don’t believe a word of it. Certainly the stickleback has a well-developed sense of territory but this only affects its behaviour towards its own species. It is indifferent to other fish, except during the breeding season. At that time it will make aggressive dashes towards any fish that comes near its nest, but they are pure show and I have never seen damage inflicted. Apart from asserting its territorial rights in its own corner against its own kind it is perfectly capable of settling down without friction with the other fish in the pool. And when it comes to dealing with insect eggs and larvae, however small and well concealed, it is absolutely without equal.

Unfortunately it will be just as ruthless in dealing with the small fry of other fish and it is for this reason that it will be unwelcome in many pools. But in any case where midge or gnat larvae proved a continuing nuisance, and provided that the rearing of ornamental fish fry was not considered important, I would not hesitate – although it goes against the general prohibition against fish from the wild – to recommend the introduction of a few sticklebacks.

But, to get back to the creatures that introduce themselves, and continuing with the insect colonists. We come to the beetles. Beetles fly readily and so they turn up in every pool in many shapes and sizes, mostly pretty small. The great majority are charming little chaps and completely harmless, but there is one big brute that totally lacks charm for the fish keeper and should be eradicated without hesitation. There is no mistaking him: Dytiscus marginalis, the Great Diving Beetle, is 1 to H in. long, blunt and powerful-looking. His colour is dark olive-brown or blackish. The thorax and wing cases edged with dull gold. The larva, which lives in the pool for two or three years before turning into an adult beetle, has a curved, segmented, tapering body up to 2 in. long, with sharp pincers at one end and bristles at the other which are not a sting but its breathing apparatus. It paddles around under water or climbs among plants with its six legs.

Both adult and larva are insatiably carnivorous and both willing and able to include fish in their diet. They suck out the body juices leaving the corpse more or less intact and fish – even up to 5 or 6 in. -found dead with no mark but punctures behind the head or on the belly are victims of Dytiscus.

It is fortunate that both adult beetles and larvae have to rise to the surface periodically to take in a new air supply at the rear end. This gives a stealthy watcher an easy target for a swoop with a net and it is not difficult to eradicate these brutes once it is realised they are present.

Very much the same comments apply to Water Boatmen, which are not much more than h in. long but are nevertheless capable of killing small fish. Their recognition features are a habit of swimming upside down, the very long hind legs working like oars, and a typical resting attitude at the surface, upside down with the tip of the abdomen and the ends of one pair of legs just touching the surface film.

I hope that these descriptions will make it easy to distinguish the wolves from the sheep because I would hate to encourage the slaughter of the many aquatic insects which do no harm at all. Remember particularly that small beetles do not grow into large beetles. When the adult beetle emerges from the pupa it is full size. If you see a beetle who looks like a dytiscus but only half the size, then he cannot be a dytiscus. Spare him.

Not all pond beetles are aquatic; some live on aquatic vegetation but never get their feet wet. Such a one is Donacia who scrapes a living from the surface leaf tissues of water hawthorn and other water plants. Donacia is not large but he gleams in the sunlight in a metallic livery of red and bronze and green bright enough to earn him the name Water Jewel. I’ve never seen Donacia in large numbers and the leaf damage never seems to amount to anything serious. As far as I am concerned any creature as attractive as Donacia is welcome to a bit of leaf tissue.

Returning generally to rest on the same favourite perch on a lily flower or reed stem. As they hawk for small insects over the pool, shining wings and metallic body colours flashing in the sunlight, you can enjoy their beauty secure in the knowledge that they are completely harmless except to gnats, midges and the like.

The larvae, or nymphs, of dragonflies are curious, goggle-eyed, six-legged uglies that crawl about in underwater vegetation, stalking and devouring small aquatic creatures. Depending on the species they may spend from one to five years in the pool before emerging to begin the few weeks of their adult aerial life.

Among the least attractive inhabitants of the pool, in appearance and in life-style, are the leeches which may be seen occasionally undulating through the water, but generally remain unobserved in the mud on the bottom. There are several species, varying in unextended length from less than \ in. to 3 or 4 in., and from olive green to dark brown in colour. Most of them prey on soft-bodied aquatic creatures such as insect larvae, tadpoles, water snails and even frogs. Fish are only occasionally hosts, except to one species, Piscicola geometra, which fortunately is of comparatively rare occurrence in garden pools. Any fish which is seen to have leeches attached to its body

I wish I could be as tolerant about the water lily beetle, Galerucella nymphaea. Anyone who grows water lilies by the acre has to take stringent pre-cations against this destructive pest. The beetle, a dull brown creature little bigger than a ladybird, and its hump-backed grub, dark grey above and yellow underneath, both feed on the top of the leaf, cutting channels in the surface tissue which darken and merge until the whole leaf blackens and decays. Its handiwork is unmistakeable, but fortunately it rarely occurs in pools containing only a few lilies, so the amateur gardener seldom sees one. If he does he should remove any leaf bearing beetles or grubs (and probably little yellow egg clusters too) and burn it. Alternatively, the lily foliage can be submerged totally by the weight of a metal ring or metal mesh and left for several days in the hope that the pests will be mopped up by fish.

An oval hole about 1 in. long in an otherwise healthy lily leaf betrays the presence of the larva of a China Marks Moth. Turn over the leaf and the chances are you will find the missing piece of leaf stuck to the underside; pull this away and you will reveal the plump green or black caterpillar, or possibly the pupal stage, snug and dry in a hammock of silk. Sometimes the caterpillar sandwiches itself between two oval leaf segments and moves around the pool. The adult moths have white wings with scribbled dark markings, and may be seen fluttering weakly among aquatic vegetation in June or July. Hand picking the caterpillars is the only way of dealing with the nuisance. It is, however, no more than a nuisance, and a mild one at that. The leaf damage it causes, although unsightly, does not seriously affect the plant.

How do leeches get into the pool? Almost invariably, I think, as eggs on aquatic plants. The plant supplier is hardly to be blamed for this since the creatures cannot possibly be eradicated from the mud of his growing tanks and the amount of time that can be spent on scrutinising the plants for eggs, among all the other pressures of the lifting season, is bound to be limited. The buyer, however, has the leisure to take a really close look at his purchases and when he has well rinsed them, as recommended earlier, I suggest that he examines every inch of leaves and stems, and scrapes off and flushes down the waste pipe any oval, flattish, dark brown capsules he finds embedded in the plant tissue. Thereby the appearance of leeches in the pool can be largely prevented. Not that they are often a serious nuisance anyway except to water snails, and snails themselves can be a nuisance if their increase is not controlled. So a few leeches may not be a bad thing; certainly they represent no risk to human beings since not one of the several British species (except for the medicinal leech which is exceedingly rare) is capable of piercing the human skin.

However, if you just can’t stand the things, or if they seem to be present in undesirable numbers, you can drastically thin them out by a simple method of trapping. You will need a small tin (such as has contained coffee or cat food), the sides pierced near the bottom with three or four holes. Put a piece of raw liver in the tin and place it on the bottom or on the marginal shelf of the pool overnight. Raise it in the morning and, if the pool has any leeches, most of them will be attached to this irresistible bait. Repeat until you find you are attracting no more customers.

One of the worst nuisances the water gardener has to contend with arrives by air; not on the wing like the insect visitors, but in the form of invisible spores borne on the wind. They are the algae, simple forms of plant life. Other kinds of algae grow in the form offline threads anchored to plant stems, pool walls or indeed anything that is handy. Many a water snail moves under a fuzz of algal threads attached to its shell. Many of these filamentous algae make only short furry growth and are harmless, even beneficial. All of them contain chlorophyll and produce oxygen and consume mineral salts in the water. None of the filamentous types discolour the water: indeed, it is often noticeable that strong growth of filamentous algae is associated with crystal clear water. Up to a point, then, they are as beneficial as oxygenating plants. Unhappily some types are capable of such rapid growth as to become a pest. They make a blanket of tangled threads that can smother other plants and even make movement difficult for fish. These are commonly known as blanketweed, silk-weed or flannelweed.

The filamentous algae are controlled and discouraged by exactly the same means as are used for the ‘pea-soup’ algae, that is, by limiting their sources of food and light through the agency of abundant submerged oxygenating plants, and the surface-covering foliage of water lilies and floating plants. Until these agencies are sufficiently developed to be effective blanketweed must be dealt with manually. I have found a Springbok wire rake the ideal tool for lifting masses of blanketweed from the spaces between containers, as well as for combing the tangled threads from aquatic vegetation. Alternatively, a rough stick twisted among the weed will draw threads from all corners of the pool to a central mass that can easily be lifted out.

Some of the recommended methods of chemical control for blanketweed are either ineffective or downright dangerous. Neither copper sulphate nor permanganate of potash can be used in sufficient strength to kill the weed without a serious risk that all other life in the pool will be killed as well. I have tested a number of alternatives and have found only one, Algimycin PLL, that really will kill blanketweed without harming fish or other plants when used at the recommended rate of 1 fl. oz. For every 250 gallons of water in the pool. Even so, care must be taken to remove manually as much of the weed as possible because any mass of dead weed left in the pool after treatment would use up much of the pool’s oxygen in the processes of decay, and this de-oxygenation could have serious consequences for the fish.

The chore of raking out blanketweed has its compensations. An examination of the mass of green cotton wool when the water has drained out of it (perfectly good mulching or compost heap material, by the way) reveals a fascinating assortment of animal life, and along with the snails and beetles and dragonfly nymphs there may be a few newts.

Newts, like frogs and toads, are amphibians that spend most of their lives on land but take to the water in spring for courtship and egg laying; the adults leave the pool when this duty has been discharged.

Newt larvae at first resemble tadpoles but very soon become miniature newts, although it is some time before the frilled larval gills disappear. I find them attractive and have never been able to adopt the ruthless attitude towards them that the protec-tion of my fish fry demands. Newts large or small will not bother adult fish but I have no doubt that they will go for fish fry as readily as any other small creature that wriggles. But I remind myself that nature intends fish fry to be very expendable and to nourish other aquatic creatures: why else would a female goldfish lay anything up to 2,000 eggs each time she spawns ? I remember too that newts consume the larvae of mosquitos, midges and other undesirables while they are in the pool, and a variety of garden pests when they are out of it.

Much the same can be said of the frogs that appear in late February or March to conduct a vigorous courtship which may involve some disturbance and kicking over of plant containers, but doesn’t last long; they leave the pool when the masses of spawn are laid. Toads are usually about a fortnight later than the frogs. Their spawn is laid in strings several feet long like jelly necklaces entwined among water plants. It is a sobering thought that every toad that arrives to spawn for the first time must have spent five years in damp corners in the surrounding garden keepingdown the slug and insect population, because it takes that long to reach sexual maturity. Frog and toad tadpoles are eaten by fish when they are small.

To the question of whether frogs, newts and toads are a good or a bad thing my answer is live and let live. Your fish will eat a lot of the tadpoles when they are small; the tadpoles will eat decaying plants and rubbish, and nibble algal growth from the pool sides; newts will eat some fish fry and many aquatic insects and your fish will grow fat on baby newts. That is the way that nature planned things and personally I see no reason to interfere with the arrangement, though I can understand that the dedicated fish breeder might well see things in a different light.

The young frogs and toads that leave the pool at midsummer disperse to damp secluded corners and do more to control your garden pests than any insecticide.

The only real blots on the record of these generally helpful creatures arise as a result of misunderstandings and they occur, I am happy to say, very rarely. The male frog in the pool for courtship in the spring is burdened with a strong compulsion to clasp his forelegs tightly round a female. Unfortunately this powerful urge does not seem to be matched by an ability to recognise what is, and what is not, a suitable object for his desire. He seems to be shortsighted, and to work on the system of- if it moves, grab it; and he frequently siezes another male frog, or a toad. Anything that moves near him and seems roughly the right size – even a moving stick or finger – is likely to be embraced. Occasionally, very occasionally, the unwilling object of the frog’s affection is a fish, and by the time the frog has realised his mistake his stranglehold may have proved fatal. In fairness it must be said that the frog doesn’t mean any harm and does not chase fish. They have to come very close before there is any risk and encounters which have fatal results are unusual.

Anyone who cannot stand the sight of frogs and toads, or the springtime goings-on in the pool, is advised to net them out and transfer them to some natural local pond. They do not need to be transported in water since they are air breathing, and a large plastic bag is suitable for a short journey. It is useless to turn them loose into either your own or a neighbouring garden; they will have found their way to the pool again almost before your back is turned.

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