Fruit Trees and Bushes Pests and Diseases
Fruit Trees and Bushes Pests and Diseases
There are a very large number of pests and diseases which can attack both top and soft fruit, but I shall only give here the ones most likely to be seen and to cause trouble. I would emphasise the importance of reading the manufacturer’s instructions carefully with these as with other food crops, particularly with regard to possible lapses of time which must be allowed between application and harvesting or, even more important, the prohibition of the use of certain chemicals on specific crops.
Fruit Trees and Bushes Pests
Aphids. Like all other plants, fruit is subject to considerable damage by these insects sucking the sap and feeding on young shoots and leaves, flower buds and so on. Blackfly, and aphids of various colours as well as the ordinary Greenfly, will all be found on fruit, and should be dealt with as soon as possible before the attack can build up, by spraying with formothion, malathion, derris or BHC. Alternatively, the dormant winter eggs can be killed with a tar-oil winter wash, with DNC, or with thiocyanate, which can be used later than other winter sprays, but in all cases read the instructions for use carefully before applying to avoid any possible damage to plants.
Apple Codling Moth. This troublesome moth appears in May and June and lays its eggs on the sides of newly-formed apple fruits. The cater- pillars enter the fruit and after feeding for some weeks emerge and let themselves down to the ground by silken threads The trees should be sprayed with an insecticide such as DDT or BHC, at the middle to end of June. Place bands of hay or sacking round the trunks in June and examine these at intervals for sheltering caterpillars and cocoons.
Remove and burn these bands of sacking in late autumn or winter.
Apple Sawfly. The small, pale cream grubs of this fly bore into the fruit, leaving a sticky mass of brown frass outside the entrance hole. They also produce a corky ribbon-like scar on the skin of the apple. The main attack occurs earlier in the season than with Codling Moth (in May and early June) and damaged fruit should be collected and burnt before the larvae leave the fruit and pupate in the ground. Spray with gamma-BHC (lindane) seven to 10 days after the blossom falls. Cultivate theunder the trees to expose the grubs or pupae to birds.
Apple Woolly Aphis. A sucking insect living on the bark and shoots of apple trees. The adult insects are protected by a mass of white fluff — hence the name. This pest can be controlled by brushing methylated spirits into the patches as soon as seen, or by spraying in early June with dimethoate or malathion and again a fortnight later — but because of the covering the spray must be forceful. Spraying with tar-oil wash in winter will also prove very beneficial.
Black Currant Big Bud Mite. This pest, a gall mite, enters the dormant buds and causes these to become markedly round and swollen. Attacked buds either develop late in the spring or are killed completely and do not open at all, with the result that the crop is considerably depleted. The mites migrate from bud to bud or from bush to bush in spring and many carry the virus disease called Reversion. Reversion causes the leaves gradually to become nettle-like and the bush produces very little fruit; for this trouble there is no cure and affected bushes should be removed and burnt, but it is possible to control the mites by picking affected buds by hand or by spraying with lime-sulphur applied at double the normal winter strength in spring, when the most forward leaves have reached 1in. in diameter.
Capsid Bug. There are numerous different species, some of which have a superficial resemblance to greenflies — but are much more active — with a similar habit of piercing leaves, stems or fruits and sucking out the sap. The parts around the puncture turn brown and produce corky warts in apples, resulting in very misshapen fruit. Spray affected fruit trees with DDT in petroleum oil just before the buds burst, or spray in spring with BHC or DDT.
Caterpillars. Caterpillars, the larvae of butterflies or moths, feed on shoots, leaves,and sometimes fruits during the spring and summer, and can do considerable damage. A spring spray with DDT or BBC repeated about 10 to 14 days later, will control them, and grease bands can be used if winter moth caterpillars are causing the trouble. The female moths are wingless and crawl up the trunks of the trees to lay their eggs, and so will be trapped by grease bands put on the trees with the greasy side outwards, not less than 1-1/2 to 2ft. above soil level, about mid-September.
Gooseberry Sawfly. The larvae of this pest are green with black spots, and will strip a bush of leaves very quickly indeed. There are three generations a year, in May, at the end of June and in mid-August, so a watch has to be kept throughout the summer, and the bushes sprayed immediately any are seen with BHC, DDT or derris, preferably with the last-mentioned after the May application.
Pear Leaf Blister Mite. This mite feeds in the tissue of the leaves from the spring to the end of the summer, and produces greenish-yellow blisters, which turn red on the upper surface of the leaf. Remove by hand all affected leaves and spray in early March with lime-sulphur, making sure that all the buds are thoroughly wetted.
Pear Midge. The small, white, maggot-like larvae of this fly hatch from eggs laid in the flowers and feed on the developing ‘fruitlets’, so that they become severely distorted and misshapen, and rather enlarged. They later fall to the ground and rot before developing fully. Pears attacked in this way can be seen from the middle of May onwards. Burning all affected ‘fruitlets’ is advisable also removing as many caterpillars as possible by hand. Also spraying with DDT when the flowers are at the white bud stage if the attack was a bad one the year before.
Raspberry Beetle. The grub of this beetle feeds on the young fruits after hatching from eggs laid in the flowers. This pest also attacks loganberries and blackberries. The fruits do not develop, but become brown and hard, or at best may ripen on one side. Spray with derris 10 days after petal fall and again about 10 to 15 days later (usually in late May and early June in the south and a little later further north), so as to kill the grubs while they are still on the outside of the fruit. Do this spraying in the evening when the bees have left the plants.
Red Spider Mite, Fruit Tree. Similar to the Glasshouse Red Spider Mite, this pest can cause a great deal of damage and severely weaken the tree or bush (it attacks apples, pears, plums, apricots, peaches, gooseberries, currants, raspberries and) by feeding on the leaves and sucking the sap out. The leaves gradually turn a greyish-yellow and dry up, and fall prematurely; cast white skins of the mite appear in patches on the under-surface. In dry, hot summers they may produce four to five generations a year, reduce the crop, and weaken the tree sufficiently for it to be killed the following winter. The winter eggs can be killed with a DNC wash applied in February or March, or by spraying with derris in late May to kill any winter eggs which may have escaped, before the adults lay summer eggs (which are not killed by derris). Chlorbenside or malathion can be used if summer eggs are laid in any quantity, and this will also deal with the adult mites.
Strawberry Ground Beetle. The adults of these pests feed on the flesh and remove the pips of the developing berries, and can damage as much as three-quarters of the potential crop. They also lay the way open to severe attacks from botrytis. Unfortunately they are difficult to control, and this is why it is important to keep the strawberry bed as clean as possible, and free from refuse, rotting vegetation, old straw and so on where the beetles can shelter. Keep the bed clear of weeds; dusting with DDT is sometimes helpful.
Fruit Trees and Bushes Diseases
Apple Canker. A fungal disease which causes the bark of fruit trees to become cracked or destroyed. It is characterised by scars and gaping wounds on the bark, often exposing the wood, and surrounded by a rugged mis-shapen rind. The shoot or branch above the canker dies and there is no more extension growth. The disease is particularly troublesome where the climate is damp and it is also more prevalent on trees growing on heavysoils, and also on certain varieties, such as Cox’s Orange Pippin. James Grieve and Lane’s Prince Albert. Bramley’s Seedling is resistant. Treatment consists of cutting away the affected shoot or branch to well below the canker if the shoot has been killed, or of paring away all the cankered tissue until healthy growth is reached, and then painting with Stockholm tar or a special wound dressing to prevent re-infection.
Apple Mildew. This disease is most noticeable in spring as a white powdery coating on the young leaves as they unfold, and on the shoots. Later, it infects the blossom as well which, instead of being pink and white (or white in the case of pears), becomes a sickly yellow. This disease can severely stunt the growth of the tree and, where it infects newly formed vegetative buds, will kill them before they can develop. Control consists of cutting out all infected growth as soon as seen in spring, and spraying with lime-sulphur or dinocap two or three times at 14-day intervals, from the green cluster stage onwards. It may be necessary to repeat the cutting out at blossom time. In winter all the shoots should be tipped back, as it is the top buds which are infected first, progressing back down the other buds on the shoot; cut so as to remove the top four or five buds. If a bud is infected it will be pointed, thin and grey, whereas a healthy bud is round and brown.
Apple Scab. A fungal disease seen every year to a lesser or greater degree, this produces roundish black spots on the leaves in spring, and spreads quickly after wet or humid warm weather. These spots rapidly increase in size and coalesce. Thealso infect the fruit, producing black patches on them which check the growth of the apple, making it distorted, and eventually result in cracking. The overwinter on fallen leaves and it is important to remove these and any prunings from around the trees.
Scab can be controlled with fungicides such as lime-sulphur or captan, making three or four applications. The first, at full winter strength if lime-sulphur is used, is given when the flower buds burst out of their winter covering and are seen as small green balls not yet showing any trace of petal colour. The second is given at the same strength about a fortnight or three weeks later when the first trace of pink can be seen in the developing blossom buds; the third is given at summer strength for lime-sulphur about 10 days after blossom can be shaken from the topmost branches; and the fourth, only necessary in severe infestations, is given in June, at summer strength Captan is given at the same strength throughout and more applications may be necessary as it is easily washed off by rain. All shoots with shrivelled bark should be removed and burnt in the autumn as well as all discarded fruits and leaves. A few varieties of apple are liable to be scorched badly by lime-sulphur and for these captan or Bordeaux Mixture should be used instead. The most notable varieties which are damaged by sulphur sprays are Lane’s Prince Albert, Beauty of Bath, Newton Wonder, Lord Derby, Rival and Stirling Castle.
Bitter Pit. A condition affecting apples which produces brown spots in the flesh of the fruit which are not apparent until the skin is removed. It is thought to be the result of unbalanced soil conditions, particularly great fluctuations in water content. The application of too much nitrogenous fertiliser appears to encourage its appearance. Good, good soil texture and well-balanced feeding are the best remedies. Spraying with a solution of 1 per cent calcium nitrate will also help, at three week intervals from mid-June to August.
Botrytis. For general details concerning this disease see Garden Pests and Diseases of Bulbs, Corms and Tubers. It is most troublesome on strawberries, and affected berries should be removed as soon as grey patches of the mould are seen. Spraying with captan or thiram two or three times at fortnightly intervals from the time the flowers open will help to keep it down, but these should not be used where the berries are going to be preserved or frozen. You can also dust with flowers of sulphur, but not within three weeks of harvesting
Brown Rot. This disease attacks many fruits including apples, pears, plums, cherries, peaches and nectarines. At first there is a brownish discoloration of the skin followed by the emergence of greyish-brown tufts arranged in irregular circles. Fruit attacked by this fungus either decays or remains in a dry, mummified condition, either lying on the ground or hanging on the trees throughout the winter. All infected fruit should be gathered and burned without delay, and any dead or withering shoots or spurs should be cut off and burned in the autumn. Spraying has little effect on this disease.
Cherry Bacterial Canker. This is primarily a disease of cherries, but also affects plums and other stone fruits. It is characterised by the sudden death of whole branches, usually accompanied by considerable exudation of resinous gum. An early symptom is the appearance of small round holes in the leaves, which also subsequently turn yellow. Cankering appears on the bark. There is no satisfactory cure. Some varieties are more susceptible than others. All affected branches should be removed immediately, and the wounds painted with Stockholm tar or a bituminous wound dressing.
Currant Reversion. see Black Currant Big Bud Mite (above)
Gooseberry Mildew, American. This disease, which is confined to gooseberries, is caused by a fungus and attacks leaves, fruits and stems. In its early stages it has a cobwebby appearance, changing to a light and powdery condition. During the summerare developed freely and are easily conveyed to healthy shoots by wind, insects and so on. Later still the changes from white to brown, and on the stems takes on a felted appearance. Spray twice with lime-sulphur wash at summer strength just before the bushes come into flower, and again as soon as the fruit is set. The varieties Careless, Golden Drop, Leveller and Early Sulphur are sulphur shy, and a spray made from a mixture of 1lb washing soda, 1lb soft soap and 5 gallons of water should be used instead. Several further applications of this wash may be needed as it is readily removed by rain and so should be applied as far as possible in dry weather.
Peach Leaf Curl. A fungal disease, Peach Leaf Curl also affects nectarines and almonds and causes the leaves to curl, become thickened and red or purple. It is usually worse in spring and is aggravated by cold weather. Remove affected leaves, and spray with Bordeaux Mixture shortly before the buds begin to swell.
Pear Canker., see Apple Canker (above)
Pear Mildew., see Apple Mildew (above)
Pear Scab., see Apple Scab (above)
Silver Leaf. A fungal disease of which the most characteristic symptom is a metallic silver appearance to the leaves, particularly on the upper surface. It attacks plums, apples, cherries, peaches and nectarines. It cannot be controlled by spraying as the sap becomes infected and, if the wood is cut into on a branch which is carrying silver leaves, the wood will be seen to be discoloured and brown. The trees sometimes grow out of it, but where it is obviously spreading the branch affected should be removed, cutting back well below the stained wood, and painting the wound with a sealing compound. To lessen the chances of infection, prune plums and cherries only between June and August. When a branch has been killed it should be burnt, not left lying bout, as the fruiting bodies then develop on it, from which new spores come to infect other branches.
Raspberry Cane Spot. A disease of the canes which shows as purple or dark spots and patches on the canes, which are spread by spores from the older canes on to the new ones as they appear and grow. Growth is stunted, leaves may be shed, and the buds may be killed. The whole bed of plants may eventually die. Spray with lime-sulphur at double winter strength in March, and at double summer strength when the first flowers open.
Badly infected canes should be cut out and burnt when seen in winter.