Post category: garden troubles

 

The maggot of this fly is so tiny that it can tunnel between the upper and lower surfaces of celery leaves, earning for itself the alternative name of celery leaf miner. It sometimes attacks parsnips leaves. If the attack comes early and in numbers, the foliage can be destroyed and growth stopped. A late attack only damages some leaves and is of no great concern.

If the attack is light – just a couple of mines per plant – it is possible to pick off parts of the affected leaves. If this is not possible Hygeia Greenfly Spray or Bio Longlast can be used.

 

Caterpillars are the larvae of butterflies and moths. Typically, caterpillars feed on the shoots and leaves of plants for a few weeks before pupating in the soil, or in a dry place, and emerge as adults some weeks later, or the following spring. They vary considerably in size. Some are only a fraction of an inch long; others can reach 7.5 centimetres.

 

Vapourer moth caterpillars on laurel

 

Caterpillar damage is easily recognised – irregular holes of various sizes, often bounded by leaf veins. The holes will have traces of caterpillar droppings, by contrast with slug damage which has slime trails.

Some kinds of caterpillar burrow into plant tissues, such as heads of cabbage and cauliflower. Practically every plant – trees, flowers, fruit or vegetables – has its own caterpillar pest, but they usually do not cause damage serious enough to warrant control measures.

Cabbage caterpillars are the major exception – they almost always cause considerable damage. Caterpillars can be picked or knocked off the plants, and killed. Batches of yellow or white eggs, often visible on the undersides of leaves, can be destroyed. If small holes appear on houseplants, a careful search may uncover a single, small caterpillar which can then be removed.

Chemical control is not usually necessary, except on the cabbage family. Suitable insecticides include a general garden insecticide or Caterpillar Spray.

 

Tiny white or yellowish maggots tunnel into carrots. If the attack takes place early on, the plants will be completely stunted. Later, the roots can be made useless if the attack is severe. After feeding in the roots, the maggots pupate in the soil, emerging as adults after a few weeks, or the following spring.

 

Carrot root fly mines in carrots

 

Parsnips are often attacked in the southern part of the country, and occasionally elsewhere. Parsley and celery are sometimes attacked too. The symptoms are the same as carrots – stunting and reddening of foliage, and small, rusty mines in the roots.

Control is quite difficult. The adult flies rarely fly above 60 centimetres; a barrier fence of polythene 60 to 75 centimetres high will keep most of them out and few roots will be affected. The barrier must have no gaps, especially at ground level. Make sure to tuck the polythene into the soil. Erect this as soon as the carrots germinate.

Growing onions or garlic with carrots to confuse the fly has given mixed results. Spent coffee grounds scattered along the row, over the root tops has given good results, but must be replaced as it is washed away by rain. Delaying sowing until May does not work in the garden because there is considerable overlap in the emergence of generations of the flies.

 

The capsids are both friend and foe! Most types of capsid bug are beneficial predators, especially in fruit trees. However, a few species cause damage to plants. Apples can have rough patches and bumps due to capsids feeding on the developing fruit but this is rarely significant.

 

Capsid bug damage

 

Dahlias, asters, and shrubs such as viburnum and choisya are often damaged quite seriously by capsids feeding on the shoot tips as they emerge – the damage only becoming apparent later on when it is to late to control the pest. Either grow something else or, in a heavy infestation, spray in May with general garden insecticide.

 

Damage is done by the root fly grubs as they feed on the roots of cabbage family plants, including radish and turnip. Wallflowers and cleome can also be attacked. Sometimes in a wet season, the sprouts of brussels sprouts can be attacked as well as the roots.

When the small white grubs reach 1 centimetre, they pupate in the soil, emerging as adults after a few weeks, or else the following spring. The adults are like houseflies and can be seen hovering around young cabbage plants prior to laying eggs in the soil.

If the attack comes early in the life of the plant, it is usually severely stunted and killed by wilting in a hot spell. The main roots will have been destroyed. If the plant is fairly big when attacked, it often grows on after the initial check.

Early digging and the removal of old crops are important in reducing the numbers of adult flies that emerge. However, they can fly considerable distances, so others will appear. Discs or squares of polythene, about 15 to 20 centimetres across, can be placed around the stem of the plants at planting out to prevent egg-laying. A slit is make halfway across so as to fit snugly around the stem of the plant as this the key point of attack. Overlap the slit, so there is no gap and no access to the soil.

 

Many different bird species can cause damage to plants. Fruit and vegetables are the main targets, being good food sources. Pigeons are major pests of all cabbage family plants, peas, raspberries, gooseberries and blackcurrants. Crows attack peas in rural areas. Bullfinches and sparrows strip out the buds of fruit trees and bushes.

 

Cauliflower damaged by pigeons

 

Blackbirds, thrushes and redwings eat strawberries, cherries, apples, pears and any sort of red berries such as cotoneaster, mountain ash and pyracantha. Starlings eat cherries and, along with crows, commonly peck at lawns to get leather jacket grubs but this is at least as beneficial as it is damaging.

Netting is the most effective solution to bird damage. Crops are only vulnerable for a part of the year and can be netted at those times. Damage to cabbage family plants usually ceases when they are about 20 centimetres tall because the birds cannot see over the plants, but if they are hungry enough, damage will continue.

Scaring devices such as strips of foil or plastic work quite well, but the birds can get used to them eventually.

 

A major pest of plants, both indoor and outdoor, greenflies can be black, brownish, reddish or blue as well as green. There is a specific type of greenflies for nearly every kind of plant, and some species have a wider range of hosts. Weakening plants by sucking out the sap, greenflies are also the main distributors of virus diseases. Unsightly, black sooty moulds often grow on the honeydew excreted by greenflies, and wasps may come to feed outdoors.

 

Curled apple leaves caused by greenflies

 

There is a limited number of plants that are frequently badly affected and need to be sprayed for greenflies. These are mostly fruit and vegetable crops and include strawberries, raspberries, apples, plums, weeping birch, japanese maple, blackcurrants, gooseberries, lettuce, beans, cabbage, brussels sprouts, roses, honeysuckle, any greenhouse or indoor plant, and herbs.

A kind of greenflies – woolly aphids – produces woolly masses on the branches of apples and pyracantha and severely weakens the plant, causing it to lose leaves and grow poorly. Control is usually necessary.

Greenflies have many natural enemies, both predators and parasites, and very often these can be left to control the greenfly population. Leaves and shoots often curl up when infested, the greenflies usually feeding within the protection provided. Even on the commonly affected plants, the natural control systems need to be supplemented only when populations look like building up early in the summer.

Controlling the first attack is usually enough to return to balance. The best product to use is Rapid, because it kills only greenflies and not the natural predators. Other products that can be used are non-persistent chemicals like Derris and Malalthion.

Systemic insecticides, which enter the plant sap, are used where the leaves are rolled up and the greenflies are safely hidden.

Soap solutions are quite effective against greenflies, and not harmful to predators. Hosing greenflies off with a jet of water can be tried too. Winter wash, with tar-oil, is effective against greenfly eggs on fruit trees, but is harmful to predators.

 

The adult vine weevil – a dark brown round-backed beetle-like insect – eats U-shaped pieces from the edge of leaves of shrubs, especially rhododendron, bergenia, euonymus and pieris, earning it the nickname of ‘ticket collector’. This damage, usually near the ground, is not significant but it is an indication of the presence of the pest.

 

Vine weevil larvae on cyclamen

 

Where there are signs of adult damage, the chances are that the white, C-shaped grubs are active below soil level. These cause severe damage by eating the roots of many kinds of plant, especially fleshy-rooted plants.

Rhododendron, strawberries, grapes, cyclamen, primula, begonia, sempervivums, saxifrages, camellias and potted plants are commonly affected. The damage to woody plants occurs usually at the neck of the plant where the bark is eaten away.

Vine weevils are more active in the warm soil of pots and greenhouses. Virtually unknown twenty five years ago, they have been spread to gardens in plant pots. Affected plants show poor growth and often wilt, though well supplied with moisture, before dying.

Damage is usually most severe when plants are grown in pots filled with peat based compost and when peat is used in the planting hole outdoors. Mixing unsterilised garden soil, half and half, with peat-based compost greatly reduces the numbers of grubs in pots because it introduces the natural predators and parasites of the vine weevil eggs and grubs. Always thoroughly mix peat with the garden soil outdoors for the same reason.

Check the roots of new plants for grubs. Clear all debris to reduce hiding places for the flightless, nocturnal-feeding, adult weevils. Provado is effective used in the compost.

Parasitic eelworms are available on order from garden centres and by post. These attack the grubs, but there must be a low level population of grubs already present before application and soil temperature levels must be at least 12º Celsius, which is common in a greenhouse but reached outdoors only in the summer months. The eelworm remedy is best applied in late July or August.

 

Barrier methods of pest control consist of physically separating the pest from its food source. They are the most effective and health-safe way of dealing with a pest problem. The pest may be actually removed physically from the vicinity of the food plant, as in removing snails near young plants or picking caterpillars off cabbage; or the pest may be excluded by netting or by fencing. Scaring may be effective too.

Physical control does not interfere with natural control systems which is a major advantage. It may be more costly and time-consuming than chemical control but there are no residues to consider. The removal of old crops and debris that harbour pests is an important part of physical control, as is early digging to expose over-wintering pests to the weather, and to predators.

Suitable barrier methods of pest control are given for each kind of pest.

 

Plants are food for many types of animal – from microscopic eelworms to large mammals – but very few of these could be called pests.

 

Wasps are both pest and beneficial predator

 

Unless an animal causes damage great enough to destroy the feature for which the plant is grown, it cannot be termed a pest. Examples of a pest species include: carrot root fly maggots that bore in the roots of carrots, making them useless; codling moth grubs that feed inside apples causing them to fall prematurely; greenflies, which by their presence, render lettuce inedible.

The simplest way to solve a particular pest problem is not to grow the pest’s food plant, but, if it is decided to grow the plants, and there are pests in the vicinity, control measures may be necessary.

 

Plants are not totally helpless against pests – they have their own defence mechanisms. The most obvious ones are thorny leaves or stems to deter grazing animals. A scaled-down versions of these are hairy plant stems, for instance, some plant hairs can be quite sharp and cause skin irritation.

 

Ragwort is posionous

 

Other plants, such as butterfly flower and petunia, have sticky plant hairs that act as miniature fly traps, making difficult the passage of greenflies and other small insects. Some plants rely on being unpalatable or poisonous. For example, plants with milky sap do not seem to suffer so much from greenflies, and the well-known insecticides – derris, pyrethrum, nicotine and quassia are all of plant origin.

Even common plants have ways of dissuading feeding animals – rhubarb is a strong laxative, the leaves containing large quantities of poisonous oxalic acid. Ragwort, bracken and yew are poisonous to grazing animals. Laburnum, daphne, cotoneaster, laurel and monkshood are examples of cultivated plants that are poisonous to a greater or lesser degree.

 

Pests have their own ‘pests’ in the form of predators and parasites. Predators are usually large and fast moving, killing and eating the pest species. Obvious examples are birds, bats, hedgehogs, field mice, frogs and foxes, which dispose of considerable numbers of insects and other pests.

 

Shield bugs kill caterpillars

 

Less well-known are the insect predators, which include ladybirds, lacewings, ground beetles, hoverflies, capsid bugs, spiders and earwigs. Most of these live off greenflies, suckers, leaf-hoppers and red spider mites.

Parasites are usually smaller than the insect they parasitise, and the pest is usually kept alive for some time before eventually dying. Many kinds of tiny flies, wasps and midges parasitise the eggs and larvae of pest species, especially greenflies and caterpillars.

Pests are attacked by diseases that play an important role in limiting their populations. For example, myxomatosis disease greatly reduced the rabbit population, although rabbit numbers have recovered considerably.

 

Nature tends towards balance. If because of favourable weather, huge numbers of a pest appear, and plant defences are overwhelmed, there are two consequences. The plants under attack fail to produce as much seed, so there will be fewer plants the following year. This means less food for the pest, causing numbers to decrease.

 

Frogs eat slugs

 

At the same time, the predators and parasites would quickly increase in numbers, there being a large population of pests to feed off. In time, the two factors would bring pest numbers back to the former level.

Natural pest control could be largely relied upon if the garden had only wild plants and wild habitat. In a garden of cultivated plants, artificial plant populations are created. Plants are grown in groups or rows, inviting pest attack.

Weeds and debris are removed, destroying the shelter of predators. A garden is an artificial situation and natural balancing systems will generally not get it right, unaided. However, the natural systems go a long way towards keeping the balance right.

Correct pest control in the garden should concentrate on encouraging, or at least not damaging, the natural systems. Only if the natural control systems prove inadequate, because of the artificiality of the garden, should they be assisted by physical or chemical control methods.

 

Chemical control consists of killing the pest with chemical poisons. It appears to be a simple solution to pest problems but there are serious disadvantages – chemicals getting onto plants may damage them or leave residues on a food crop. Harmless, potentially beneficial insects might be killed.

To make chemical control safer and more acceptable, the chemicals nowadays offered for sale are less poisonous and less persistent, meaning it is less likely there will be residues and, if there are, they will be less dangerous. Chemical control is cheap and easy – perhaps too easy.

Because of the disadvantages, chemical control should be used only when there is no other solution. Routine spraying is to be avoided, unless absolutely necessary, because it leaves excess residues, damages the natural balance and encourages the evolution of resistant strains of the pest. Not only is unnecessary spraying a waste of time but it can be very counterproductive.