PESTS OF THE FRUIT GARDEN
By sucking the sap, aphids can cause devitalization and reduction of crop on all types of fruit. The eggs are laid on the bark in the autumn and infestation starts when they hatch in the early spring. The young insects are usually hidden deep in the folds of the developing leaves, but their presence is often betrayed on sunny days by ants, which run up and down the trunk feeding on the sugary honeydew excreted by the pests. If aphids are not dealt with in the early stages they will quickly multiply and cluster on the young shoots and on the underside of young leaves, often causing them to become severely distorted and, in some cases, discoloured.
It is possible to deal here with only a few of the more common species of aphids which infest fruit, but, with few exceptions, notably the easily recognized Woolly Aphid on apple, the control measures recommended are adequate for all species.
Apples are attacked by the Green Apple Aphid and the Rosy Apple Aphid which cause curling of the young leaves at the tips of new shoots. The latter species also attacks young fruits, causing them to become stunted and misshapen. The purplish-brown Woolly Aphid is distinguished by the masses of white ‘wool’ which cover the colonies. This species feeds on bark and causes the formation of swollen tumours, which later tend to split as the wood grows and thus allow disease organisms to enter.
Currants are attacked by the whitish Currant Blister Aphid, which causes the formation of raised blisters on the leaves. These blisters are usually a reddish-brown, but on black currants may be yellow. The green Currant-Lettuce Aphid causes the terminal leaves to curl tightly and become mottled with yellow.
Gooseberries are most likely to be infested by the Lettuce Aphid, and the symptoms of attack are the formation of small curled leaves at the tips of the shoots.
Pears are not so likely to be damaged by aphids as other fruits, but the Pear-Bedstraw Aphid may occasionally be troublesome, curling the young leaves.
Plums are often severely crippled in the spring by the Plum Leaf-curling Aphid, which causes the leaves to become tightly curled and coated with sticky honeydew. Later, in the summer, the foliage may be attacked by the Mealy Plum Aphid which covers the underside of the leaves. It is a pale green species with a white powdery covering. It does not cause leaf-curling but may cause the leaves to fall prematurely.
Raspberries may be damaged by the greyish-green Raspberry Aphids, which congregate at the tips of the canes causing curling of the young leaves.
Strawberries are very prone to aphid attack, especially by the greenish-brown Shallot Aphid, which causes the leaves to become twisted and the flower trusses stunted, and by the Strawberry Aphid, a pale creamy-coloured insect which is an important carrier of virus diseases.
Control of Woolly Aphids
Spray with lindane or malathion at the pink-bud stage of apple blossoms. Colonies seen after blossom should be sprayed only with malathion or else painted with 10 per cent tar oil.
Control of other aphids
Kill the over-wintering eggs on tree fruits, currants and gooseberries by spraying every fourth year with 5 per cent tar oil in December or early January when the plants are completely dormant. During the intervening years apply sprays in spring as follows:
Tree fruits — D.D.T. Emulsion, lindane, malathion or nicotine between bud-burst and the appearance of the green blossom buds.
Currants — D.D.T. Emulsion, malathion or nicotine just before the flowers open (late ‘grape’ stage).
Gooseberries — D.D.T. Emulsion, malathion or nicotine immediately after blossoming.
Raspberries — Tar oil each winter.
Strawberries — Malathion or nicotine just before flowering and again after picking.
Outbreaks of aphids during the summer should be dealt with by spraying or dusting with malathion or nicotine.
APPLE BLOSSOM WEEVIL
The Apple Blossom Weevil, formerly an important pest, is now easily controlled by D.D.T., but may still be found in great numbers in neglected orchards, particularly near woods. The adult weevil lays its eggs on the unopened flower buds of apple and sometimes of pear. The whitish grubs which hatch out feed inside the buds, prevent them from opening and cause them to wither, so that these brown ‘capped’ blossoms are noticeable after the other blossoms have shed their petals. The grubs, or yellowish pupae, are usually found inside the blossoms if they are opened.
Apply D.D.T. at the bud-break stage. One application should give adequate control for a number of years.
‘Big Bug’ Mite
The ‘Big Bud’ Mite, or Black Currant Gall Mite, microscopic in size and in-visible to the naked eye, invades the buds of black currants in vast numbers, and the buds become globular and swollen to about twice their normal size. Infested buds usually wither and die without producing leaves, and the general effect is a progressive reduction in the yield of fruit.
The mite is also responsible for the spread of the virus disease known as ‘Reversion’, which also causes gradual deterioration of yield.
The complete eradication of this mite is extremely difficult. The bushes which are badly affected either by ‘Big Bud’ or ‘Reversion’ should be dug out and burnt. On newly planted or lightly infested bushes, keep the pest in check by spraying with 2 per cent lime sulphur just before the blossoms open, and again with l per cent lime sulphur three weeks later.
Capsid bugs are fast-moving, active insects which resemble aphids when young but grow to about 1/4 in. long. They feed by piercing the leaves or fruit and sucking the sap.
The Apple Capsid feeds on the leaves of apple and causes some distortion. Damage to the fruit is, however, more serious, and where the insects have fed, rough brown patches appear on the surface of the skin which may also be raised like a wart. Although attacked fruit may be unsightly, the flesh is usually perfectly sound and the apples can safely be stored.
The Common Green Capsid attacks a wide variety of soft fruits and tree fruits. As with the Apple Capsid, rough brown patches appear on the skin of pears and plums which may also be distorted and split. On bush fruits such as currant or gooseberry small brown spots develop on the young leaves which become distorted and torn as they grow.
Spray tree fruits with D.D.T. or B.H.C. When the blossom buds are still green. Currants and gooseberries should be sprayed with D.D.T. only; the currants just before flowering (‘grape’ stage) and the gooseberries just after flowering.
Caterpillars of one type or another are common pests on fruit, particularly tree fruits, and those which feed on the foliage can reduce the leaf area so much that crops suffer a severe check. Some, such as the Codling Moth caterpillar, damage the fruit itself.
Codling Moth caterpillars are among the most common and destructive of apple pests and, together with the larvae of the Apple Sawfly, are responsible for the condition known as ‘maggoty apples’. The Codling caterpillar is pink-coloured and enters either near the ‘eye’ of the fruit or by a hole in the side which is often surrounded by a red ring. It burrows into the apple and feeds round the core. If attacked apples do not fall prematurely, the mature caterpillars descend the trunk from late August onward and hibernate in cracks and crevices in the bark. The control measures are quite different from those used against the Apple Sawfly, and it is therefore important to be able to distinguish these two pests.
Provide the caterpillars with hibernating quarters by tying corrugated paper or loose sacking round the tops of the trunks in mid-July, removing and burning them during the winter. Pick up and destroy all prematurely fallen fruit. Spray the trees with D.D.T. In mid-june and again three weeks later, adding malathion or derris to keep red spider in check. Fruit Tree Tortrix Moth caterpillars are small, greyish-green creatures. In the spring or early summer they feed on the leaves of apple and other tree fruits after rolling them up or tying them together with silk webbing. Later they may attach a leaf to a developing fruit and feed underneath on the skin, making small holes which appear unimportant but which allow the entry of disease organisms. Fruit damaged in this way cannot be stored.
Apply D.D.T. when the green flower buds appear.
Caterpillars of the Winter Moth and its relatives feed on the foliage of apple, pear and plum from April to June, and also on the flower trusses and the developing fruitlets. They are green with pale lines along their bodies. A curious feature of this species is that the female moths are wingless and must climb the tree trunk to lay their eggs.
Spray with D.D.T. When the green flower buds appear. If spraying is not possible, apply tree-banding grease in a 3-in. band round the trunk before the end of September, to prevent the wingless female moths from climbing into the branches to lay eggs.
The Pear Midge is a small fly which lays its eggs in the flowers of pear. The leg-less white maggots which hatch out bore into the young fruitlet and feed inside. The fruitlet then becomes abnormally swollen and rounded, and when cut open a blackened cavity containing the maggots is revealed. The fruit later falls to the ground where it cracks and decays, allowing the mature maggots to escape.
Spray with D.D.T. At the white-bud stage. Infested fruitlets should be picked off and destroyed before they fall.
The Raspberry Beetle is the pest responsible for ‘maggoty’ raspberries and loganberries. The brown adult beetle damages the flowers, but more serious damage is done by the grub which, in its early stages, feeds first on the outside of the developing fruit, causing it to become hard and brown, and later tunnels into the plug of the fruit and feeds on the flesh from the inside.
Spray with derris or D.D.T. 10 days after full bloom, and again 10 days later.
RED SPIDER MITE
Red spider mites are very small creatures which suck the sap on the under-surfaces of leaves. They are distantly related to insects or spiders and, in spite of their name, their colour is more usually orange-green than red. Although the fully grown adults are smaller than a pin-head, they can, when present in large numbers, cause considerable damage which results in a general weakening of the plant.
The Fruit Tree Red Spider Mite is particularly harmful on apple, plum and damson. In the early stages of the attack the leaves become dull and speckled finely with yellow. Later the foliage may take on a silvery appearance due to air entering the damaged cells, followed by bronzing and premature leaf-fall.
To kill the over-wintering eggs, spray with D.N.C.-petroleum between the end of February and the bud-break stage. During the summer spray in early June with malathion or derris and repeat twice at H-day intervals. Apply the spray to the underside of the leaves.
The Gooseberry Red Spider Mite infests the leaves of gooseberry which then become pale and sickly-looking, and may later wither and drop off.
Spray the underside of the leaves with malathion or derris when flowering has finished. Repeat twice at 14-day intervals and pay particular attention to the centre of the bush.
Sawfly larvae resemble the caterpillars of moths and the damage done by the two types of pest is very similar.
The Apple Sawfly is a common pest of apple, and its larva is often confused with that of the Codling Moth.
Attacks by sawfly larvae are usually seen first in May, and they eat more of the flesh than does the Codling caterpillar which attacks in July and feeds mainly on the core.
Other differences between the attacks are that apples infested by sawfly larvae have an obnoxious smell when cut open, and fruits attacked by these larvae often display long ‘ribbon’ scars on the surface, the result of the young larvae burrowing under the skin.
Spray with lindane at petal-fall.
The Plum Sawfly attacks plums and damsons. The small white larva enters the young fruitlets, leaving a small hole which oozes a sticky, black fluid. It attacks more than one fruit, tunnelling in the flesh and causing premature dropping.
Spray with lindane eight days after petal-fall.
The Gooseberry Sawfly has green, caterpillar-like larvae with black spots, which feed rapidly on the foliage of gooseberries, eating all but the mid-ribs. Eliminate this pest as soon as it is seen since it can do serious damage in a very short time.
Spray or dust with malathion, D.D.T. Or derris after the fruit sets or as soon as an attack is seen. Pay particular attention to the centre of the bushes where the infestation is often severe.
Scale insects, which are usually found only on neglected fruit trees and bushes. The Brown Scale, which is chestnut-brown, about 1 in. long and very convex, may be found on the bark of plums, peaches and soft fruits. The Mussel Scale, much flatter, is grey and shaped like a miniature mussel shell. It is found mainly on apple trees but can occur on almost any tree or bush fruit.
Apply a tar oil wash in December or in early January.
Slugs attack strawberries, raspberries and gooseberries.