Fruit problems FAQs

What causes some of my apples to turn brown and rot while still on the tree?

Brown rot of apples is a fungal disease (caused by Sclerotinia fructigena and S. laxa) which enters the fruits through wounds made by insects or birds. It cannot be controlled by spraying with fungicides, but you should remove and burn any infected fruits on the tree or on the ground. Apples showing even slight signs of rot should be trimmed of their damaged areas and used immediately and not stored; apples in store must be inspected regularly for signs of rot.

This summer clumps of white woolly mould growth have developed on the branches of my apple trees. Can you identify this disease?

These are clusters of woolly aphids (Eriosoma lanigerum), the greenfly being covered with a waxy material which looks like a mould; the pest is sometimes called American blight. The aphids feed by sucking the sap and cause warty growths to develop on the branch, which may split and become cankered. Control them by applying a forcible spray of general insecticide.

The young leaves on the tips of the shoots of my cherry tree have become curled and distorted. What causes this trouble?

If you examine the shoots you will find that inside the curled up leaves are colonies of cherry blackfly (Myzus cerasi). These hatch from eggs laid near the buds in the previous autumn, so the pest can be controlled by applying a tar-oil winter wash in December or early January. Alternatively, a systemic insecticide should be sprayed on the trees at bud burst. It is most important to control this pest as it stunts the new growth and affected branches may die back.

Dull olive-green patches have appeared on some of the leaves of my apple trees and dark brown scabs are showing on a few of the young fruits. What caused this trouble?

Both disfigurements are caused by apple scab (Venturia inaequalis), which not only infects leaves and fruits but can cause small cankers on young twigs. If left unchecked it can ruin the appearance of the fruit and also lead to early defoliation. Control it by a programme of sprays of benomyl, sulphur, thiram, or triforine, which should be applied when the green flower buds first appear, at the pink bud stage, at petal fall, and again three weeks later.

The leaves on one of the branches of my ‘Victoria’ plum tree have turned silvery. What can be causing this effect?

This branch has become infected with silver leaf (Stereum purpureum). The fungus invades the branch, staining the wood purple and producing a toxin which moves upwards in the sap, causing the leaves to become silvered. Later the infected branches will die back and small bracket-shaped fruiting bodies may develop on the dead wood. Cut back the infected branch to well below where the wood is stained and then paint the wound with a canker plant.

Before taking this drastic action, however, make sure that the trouble is not due to false silver leaf. This physiological disorder can be distinguished from true silver leaf by the fact that most of the leaves become silvered at the same time; moreover, there is no staining of the wood. False silver leaf is caused by a combination of malnutrition and fluctuating water supply. The immediate first-aid is to apply a foliar feed. Next season, feed, mulch, and water the tree as necessary.

This year I found that the cores of many of my apples had been eaten away and become rotten. In some fruit there were small caterpillars. How can I prevent this happening next year?

Your apples have been attacked by the caterpillars of the codling moth (Cydia pomonella). This moth lays its eggs on apple leaves and fruitlets, and the young caterpillars tunnel into the developing fruits. They leave the fruits in mid-August to pupate. Codling moth can be controlled by applying a general insecticide in late June and again in early July. The non-toxic, highly persistent insecticide permethrin is particularly effective against these pests.

Some of the emerging shoots and flower trusses on my apple trees are covered with a greyish-white powder. What caused this trouble and how should I deal with it?

The shoots are suffering from apple mildew (Podosphaera leucotricha). The infection will have occurred last summer, but it does not show up until the buds begin to grow. The infected growth will remain stunted and unfruitful. Your first job is to cut off and burn the diseased growths, otherwise they will be sources of infection for the rest of the tree. Follow this up by applying a series of sprays at fortnightly intervals using fungicides based on benomyl, bupirimate, dinocap, thiophanate-methyl, or thiram.

Rounded holes have appeared in the leaves of my plum tree but there is no sign of caterpillar attack. What’s the explanation? bacterial canker (Pseudomonas mors-prunorum), which also attacks cherries. Infected leaves first develop brown circular spots, and then the centres drop out leaving the shot-holes you mention; cankers, exuding gum, also appear on the branches, which may die back. To protect them against this disease, spray the trees with a copper fungicide in August, September, and October. Any branches which die back should be removed.

Many of the youngest leaves on my peach tree have developed reddish blisters, while the slightly older ones are swollen, distorted and covered with a whitish bloom. What is happening?

Your peach tree has been infected by peach-leaf curl (Taphrina deformans), which not only distorts the leaves but also causes them to fall prematurely, thus weakening the tree and seriously reducing cropping. Spray the tree with a copper fungicide in late January and again in early February.

The appearance of some of my apples has been ruined by a spiral, ribbon-like scar leading towards the eye of the fruit. What is the cause, and how can I prevent it in future?

This trouble is almost certainly

Your fruits have been attacked by caterpillars of the apple sawfly (Hoplocampa testudinea), which hatch from eggs laid on the flowers. They not only cause this surface damage but, if they penetrate the fruit, they will bring about early fruit drop, thus reducing the crop. Control them by applying a general insecticide after the blossom has fallen.

The foliage towards the centre of my blackcurrant bushes is being eaten away by large green, black-spotted caterpillars. What spray should I use to control them?

The caterpillars are larvae of the blackcurrant sawfly (Nematus olfaciens). They are somewhat resistant to chemical control, but try spraying them with an insecticide based on permethrin or trichlorphon. The alternative is hand picking. I suggest that next year you examine the centres of bushes regularly in May and June and, if necessary, spray them when the caterpillars are still small.

Many of the buds on my blackcurrants have become rounded and swollen. They have either failed to open or have produced only small, deformed flower trusses. What caused this trouble?

This condition is known as ‘big bud’ and is due to the buds becoming infested with a tiny gall mite (Cecidophyopsis ribis). In early summer the mites leave the old buds and invade new ones on the current season’s growth. Not only does this pest greatly reduce the harvest you are likely to obtain from your bushes, but it can also transmit a weakening virus disease known as ‘reversion’, that will threaten the production of currants in future seasons; so it is important to take control measures. Pick off and burn any enlarged buds during January to March and then apply a series of sprays with the fungicide benomyl, starting when the first flower buds begin to open.

Returning from holiday I was shocked to find the leaves on my gooseberry bushes completely eaten away apart from their mid-ribs. What can have caused such severe damage?

Your bushes have been attacked by caterpillars of the gooseberry sawfly (Nematus ribesii). These large green, black-spotted caterpillars start feeding in the centre of the bush so although they are very conspicuous, they are not easy to spot at first. To avoid this kind of damage in future you should inspect the bushes regularly during April and May, picking off any caterpillars you find. Alternatively, spray in April and again in May with an insecticide containing permethrin.

Blackish scabs are developing on the young fruits of my pear trees and dull olive-green patches are showing on the leaves. Can you identify this disease and advise on its control?

Your pear trees have been attacked by pear scab (Venturia pinna), which has symptoms similar to those of apple scab although it is a different fungus. Like apple scab it damages the fruit, causes early defoliation, and can produce small cankers on the young twigs. Control it by spraying with benomyl, sulphur, thiophanate-methyl, or thiram at bud burst, when the flower buds show white, at petal fall, and finally three weeks later.

Small yellow spots have appeared on the upper surfaces of the leaves on my plum tree and on the undersides of the leaves there are small orange-brown powdery dots. Is this some form of rust?

The symptoms you describe are typical of the early stages of plum rust (Tranzcheiia pmnispinosae var. discolor). Later, the powdery spots turn dark brown or black and the leaves generally fall prematurely. Rake up the fallen leaves and burn to reduce carry-over of the disease. Next year keep a close watch on the tree and spray it with a fungicide based on mancozeb or thiram at the first sign of attack.

A few shoots on my blackcurrant bushes have died back and now small raised orange spots are appearing on the dead bark. How can I prevent this disease from spreading?

This disease, known as coral spot, is caused by the fungus Nectria cinnabarina, which enters the plant through small wounds and pruning snags. Remove and burn any dead branches cutting them several inches below the dead growth and sealing the cut surfaces with a proprietary wound paint. It is also a good idea to clear away and burn any woody debris such as old pea sticks as these are often infected with this fungus.

The leaves, shoots, and fruits of my gooseberries have developed a white powdery covering. Is this some sort of mildew?

The symptoms you describe are typical of American gooseberry mildew (Sphaerotheca mors-uuae), an all-too-common disease that not only weakens the plants but spoils the fruit. Prune the bushes to keep the stems well spread, taking care to remove and burn any diseased shoots. Next spring, starting just before the flowers open, apply 2-3 sprays at fortnightly intervals using a fungicide based on benomyl, bupirimate, or thiophanate-methyl.

On picking my raspberries I found that many of the fruits were infested with tiny white maggots. How can I avoid this trouble in future?

Your fruits have been attacked by the raspberry beetle (Byturus tomentosus), which can also infest blackberries and loganberries. The beetles lay their eggs on the flowers and the grubs hatching from these feed on the developing fruits. Spray with an insecticide based on derris, malathion, or permethrin. Raspberries and loganberries should be treated when the first fruits are colouring, but blackberries should be sprayed as soon as the first flowers open.

The tips of some of the new canes of my raspberries have died back and I now find that the canes have developed oval greyish spots which are splitting in the middle. Can I take any action to remedy this trouble?

Your raspberries are infected with raspberry-cane spot disease (Elsinoe ueneta). The infection shows up from early June onwards as small purple spots, which later run together and give the effects you describe. Cut out and burn any badly spotted canes. Next spring give a series of sprays with benomyl, copper, or thiram from bud burst until just before flowering.

In recent years the cropping of my raspberries has become very poor. The canes are stunted and the leaves distorted and mottled with yellow. What should I do to improve the cropping?

Your raspberries have clearly become infected with one or more virus disease or by mycoplasmas. Unfortunately there is no cure for this type of infection so you should dig up and burn your present plants. Replace them with certified healthy stock, planting these on a fresh site well away from the previous planting.

Something seems to have eaten the seeds and some of the flesh from many of my strawberries, completely spoiling their appearance. I can see no sign of any pest and would like to know what is causing this damage.

The culprit is a shiny black beetle called the strawberry-seed beetle (Harpalus rufipes), which hides under plant debris. Keeping down weeds and removing dead leaves reduces their numbers. Further insurance against attack is given by spreading slug pellets based on methiocarb among the plants.

Purplish patches have appeared on the leaves of my strawberries; the edges are beginning to curl upwards, while the undersides have turned greyish in colour. Is this some type of disease?

Your strawberries are showing the early stages of infection by strawberry mildew (Sphaerotheca macularis); it can also occur on the flowers and fruits, giving them a dull and shrivelled look. Repeated sprays of benomyl, bupirimate, or thiophanate-methyl should be applied at 10- to 14-day intervals until the fruits begin to change colour. Cut off and burn the old leaves after harvesting.

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