Diseases of Fruit, Vegetables and Flowers

A guide to what they are and how to cure and prevent them.

(Alphabetical order in each section)

General

DAMPING OFF DISEASE

This disease is extremely common on most seedlings and causes the small plants to rot off at soil level. It is usually caused by a combination of any, or all, of the following reasons - crowding of seedlings, over watering, lack of air circulation, dirty containers and contaminated soil or contaminated water. Always sow seeds thinly in fresh sterilised compost in clean pots. Water sparingly with fresh tap water, preferably using Cheshunt Compound or some other copper based fungicide and ensure adequate ventilation.

SOOTY MOULD

This is a black fungus that grows on the sticky secretions of aphids. Control of the aphids will stop the problem.

Vegetables

ANTHRACNOSE

This fungal disease is normally associated with cool damp growing conditions. The main symptoms are brown spots on the stems and withering. Spray with a copper based fungicide but only until they begin to flower. Destroy plants after cropping and avoid growing beans in the same position for a couple of years, as the disease is seed borne.

BEET RUST

This is a less severe fungal infection of Beetroot, which causes small red/brown spots under the leaves. It is most likely to be seen in autumn. Pick off infected leaves and spray with Captan or Zineb.

BLACK ROT

A disease found on stored roots, which shows as black sunken patches near to the neck. No control is known and the infected roots should be destroyed.

BORON DEFICIENCY

Most likely to occur on light sandy soils or very limey soils, in dry weather. The symptoms are commonly called crown or heart rot, in which the central leaves die and become black and roots may also turn black inside. Ensure that the ground has plenty of organic matter incorporated and fed with a liquid seaweed feed or fertiliser.

CELERY LEAF SPOT

Brown spots appear on the leaves and develop into black pustules. Most seed purchased is treated against this virus but self-saved seed may succumb to it. Spray with a fungicide such as Bordeaux mixture every fortnight until just before harvest.

CHOCOLATE SPOT

This affects Broad Beans and shows as brown spots on the leaves. In severe cases the stems will turn black. Spray with a copper based fungicide such as Bordeaux mixture.

CLUB ROOT

This devastating disease affects Brassicas, Swedes, Radish and Wallflowers. It is caused by a soil borne fungus that causes the roots to thicken and distort. It is much worse on badly drained and acid soil. It survives in the soil indefinitely and can be transmitted via the soil stuck to your boots to other areas of the plot. There is no cure for it but various methods can be used to reduce its effects. (See separate article on Club Root)

CROWN GALL

This is a bacterial infection associated with badly drained soils and causes lumps on the sides of root crops. Correct any drainage problems before replanting.

CUCUMBER MOSAIC VIRUS

This disease attacks all the Squash family. The leaves turn yellow and pucker and growth is stunted. Destroy affected plants, as there is no cure. Prevent by controlling the aphids that carry the disease.

LEAF MOULD

This shows on fruit trees as the top surface of the leaf being yellow and the underside brown. Most modern varieties of fruit are resistant to it. If older varieties are affected, spray with a copper fungicide.

GANGRENE

This fungal disease affects Potatoes in storage and causes them to rot. Only damaged or wet Potatoes are likely to get it. Ensure that only dry undamaged Potatoes are put into storage.

HALO BLIGHT

Brown spots on the leaves surrounded by a lighter halo. As it is seed borne and usually treated by seedsmen it is not very common and will only be found if using your own saved seeds.

LEAF MINER (MANGOLD FLY)

Small white grubs that burrow inside the leaves leaving brown blisters. Pick off infected leaves and spray with Malathion.

MAGNESIUM DEFICIENCY

Magnesium is one of the major constituents of chlorophyll. Signs are a paling of the leaf between the veins, which eventually turn brown and die. It most often occurs in very acid or very limey soils. Check pH and rectify. An application of Epsom salts applied at the rate of 2oz per gallon of water and sprayed on the foliage at fortnightly intervals will also help.

MANGANESE DEFICIENCY

This causes yellow speckles on the leaves, which may tend to turn up. Very sandy and very alkaline soils may be deficient in Manganese. In severe cases apply a foliar feed of Manganese Sulphate at the rate of 2oz per 5 gallons of water.

MOSAIC VIRUS (and Yellow Virus)

Sometimes known as Spinach Blight, it affects the leaves by turning them yellow. It is spread by Aphids. There is no cure for it, and affected plants should be destroyed. Prevent infection by controlling the Aphids.

NECK ROT

This shows as a white fungal growth on the roots. Affected plants will wilt and die. Treat with a copper based fungicide such as Bordeaux mixture. Do not replant with bulbs for at least two years to help eradicate any spores. Drenching the area with a disinfectant such as Armillotox may help speed things up.

PARSNIP CANKER

This disease causes brown marks around the neck of the root. Use only resistant varieties.

PEA THRIPS

Silvery patches appear on pods, which are distorted. Attacks are worse in dry weather.

POTATO BLACKLEG

This bacterial disease causes the stems to go black and rot. Remove and burn infected plants and tubers. Only plant certified tubers.

POTATO BLIGHT

This first shows as black or brown blotches on the leaves. More severe cases will show as the plant turning yellow and eventually dying. The tubers will not store and will rot. Treat by spraying the whole crop with a copper based fungicide such as Bordeaux mixture.

RUST (vegetables)

Attacks mainly Leeks and shows as a bright orange pustules. Difficult to control but Myclobutanil is reported to have some effect on it.

SCAB (general)

This disease is usually associated with limey soils. Symptoms are sunken pits or raised lumpy bits on the skin. These increase in size so that the root becomes distorted. Although it does not kill the plants it detracts from the appearance and makes it less pleasant to eat. Ensure that the pH of your soil is correct.

SCAB (POTATO)

This disease causes ugly marks on potato tubers. Avoid trouble by incorporating plenty of organic matter into the soil and watering well during dry weather. Use resistant varieties.

SCLEROTINA ROT

This occurs under incorrect storage conditions of Carrots. It causes white fluffy mould to grow on or near the neck of the root. Black spores develop and then infect other roots. Ensure that there is plenty of ventilation to the roots and only sound roots are stored. Remove any roots that are infected.

SOFT ROT

This is a bacterial disease affecting Turnips and Swedes. It shows as a grey or white mushy rot. Worse on badly drained soil. Rotate the crop and increase drainage to prevent.

SPRAING

This causes red or brown marks in the flesh of Potatoes. There is no cure but some varieties are resistant, it would be advisable to grow these in future.

VIOLET ROOT ROT

This is a serious fungal disease that is soil borne. Signs are wilting of the plant and yellowing of the leaves. When lifted, the roots have a web of purple threads around them. It particularly affects Beetroot, Parsnips, Carrots, Asparagus, and Potatoes. There is no cure and infected crops should be dug up and destroyed. Do not replant with any susceptible crops for a period of three years.

WHITE ROT (onions)

This shows as a mouldy growth near the neck of the onion, which then rots. Remove bulbs and do not put into store. Spraying with a fungicide may help if caught early enough.

Fruit

BACTERIAL CANKER

This affects Plums, causing round holes to appear in the leaves and a sticky gum leaching from the branch. Cut out infected areas and spray with a copper fungicide from midsummer to autumn at fortnightly intervals.

BACTERIAL CANKER (STEMS)

These cankers are flat and may not be easily noticed but gum may ooze out. The effect on stone fruit will be serious. Cut out the canker to clean wood and treat the wound with Arbrex.

BITTER PIT

This calcium disorder causes brown sunken patches on the skin of Apples. It may be seen while on the tree but it usually shows up when put into store. Ensure a plentiful supply of water in dry weather.

BLACKCURRANT RUST

This causes yellow patches on the underside of the leaves in early summer. Spray with Dithane immediately after harvest.

BLOSSOM END ROT

This causes the bottom of Tomatoes to turn black. It is a physiological disorder related to calcium. Regular and even watering helps to prevent the problem.

BLOSSOM WILT

This disease gives the effect that the tree has been scorched. It affects Plums, Apples and Pears. The blossom trusses wilt and turn brown and in a severe attack the shoots may die back. It is more common in mild wet springs.

BROWN ROT

This is a common sight on Apples. The fungus enters through wounds on the fruit, made by birds or wasps, and turns the fruit brown and soft. It eventually becomes covered in rings of white mould and the fruit drops to the ground. There is no cure for this, but pick of any infected fruits to avoid contaminating the others. It can also affect fruits put into store, so ensure that only perfect fruit is stored and it is checked regularly.

CANKER

A very common disease of Apple and Pear trees. It shows as sunken patches on the bark with white fungus around them. The stem swells and spreads around the branch. When it completely encircles it, the branch dies. There is no cure or prevention and infected branches should be cut out and burned.

CANE BLIGHT

This attacks Raspberries and shows at the bottom of the canes as a brown patches and a withering of the leaves. Cut out infected canes and spray the rest with a fungicide such as Benomyl.

CANE SPOT

This attacks Raspberries and shows up as small purple spots, which spread and split. Cut out affected canes and treat with a fungicide such as Benomyl.

CORAL SPOT

This can affect all woody plants and shows up as bright red spots and eventually the branch will die. It infects by penetrating wounds or pruning cuts. There is no cure so cut out and burn any infected branches.

DIE BACK

This affects Gooseberries and is caused by a fungus. A whole branch and leaves will suddenly die and the foliage turns yellow and drops. Remove affected branches and treat cuts with Arbrex. Spray the whole plant with a fungicide.

FIREBLIGHT

This is a serious and increasingly found disease. The disease enters through flowers and rapidly spreads to the rest of the plant. The leaves remain attached and the plant looks as if it has been burnt. Treatment involves cutting out infected branches or in serious cases removing the tree itself.

FOOT ROT

The base of the stem turns brown and the plant collapses. If affected remove plants and destroy. Ensure that sterile compost is used when planting and avoid over watering.

GREY MOULD (BOTRYTIS)

This fluffy mould affects most soft fruit and is more prevalent during wet summers. Remove any plant material that is affected and ensure that the plants are sprayed with a fungicide as a precaution.

HONEY FUNGUS (Bootleg Fungus)

This affects all woody plants and trees, including ornamentals. It causes white growths under the bark and brown threads in the roots, which is how it gets its alternative name. In the autumn honey coloured toadstools appear above ground. Remove any dead or dying plants and treat the area with a phenolic emulsion. This is normally done by making holes around the infected area, 2 feet deep with a bar and pouring the liquid into these holes.

HORMONE DAMAGE

This can caused thin distorted leaves and is usually caused by cross contamination from a weedkiller that has been used elsewhere. Many lawn weedkillers contain hormones. Never use sprayers or watering cans that have been used for weedkillers to water plants.

LEAF SCORCH

This can affect all fruit and causes brown edges on the leaves. The growth of the plant is stunted and fruit is very small. It is caused by a Potash deficiency. Ensure that the plant is well fertilised and if the disease is noticed, water with a high Potash fertiliser (Tomato Feed).

LEAF SPOT

This disease affects Blackcurrants and Gooseberries. Brown spots appear on the leaves, which then drop off. This weakens the plant and the following years crop is reduced. Spray with a fungicide as a precaution at fortnightly periods. Ensure that any leaves that have dropped from the plant are removed and burned.

LEAF ROLL

This problem usually applies to Tomatoes. Unlike Potatoes, the curling does not indicate a disease. Inward rolling of young Tomato leaves is usually taken as a good sign if the leaves are dark green. The rolling of older leaves is a sign that too much foliage has been removed from the plant or a wide variation of temperatures.

LEMON SCAB

This is a fungus disease that affects citrus fruits and causes corky ridges on the skins. Spray with copper fungicide when half the petals have fallen.

LITTLE LEAF

This problem is caused by a zinc deficiency. The leaves become mottled and crinkled and the fruit is deformed. Regular mulching with well-rotted manure or compost will prevent trace element deficiencies or feed with a seaweed fertiliser.

MAGNESIUM DEFICIENCY

MILDEW (POWDERY)

This attacks most fruit trees and bushes, causing a silvery coating on the shoots. On Gooseberries it also covers the fruits. Spray with a fungicide when the flower buds turn green and then at fortnightly intervals. Some fruit varieties are resistant to Mildew.

MILDEW (AMERICAN)

Very similar to ordinary Mildew but is more commonly found only on Gooseberries and is encouraged by overcrowding. Spray with a fungicide at the first signs and then at fortnightly intervals. Ensure that the bush is kept well pruned and of an open nature.

PEACH LEAF CURL

This disease affects Peaches, Nectarines and Almonds and causes red blisters to appear on the leaves, which eventually turn black and fall off the plant. It is important to treat early with a copper-based fungicide. Treat in late winter and again two weeks later and then again in autumn. An organic method is also used whereby the plant is protected from rain between January and late may. This prevents the fungus spores from touching the plant.

PEAR STONEY PIT

This is a viral disease of Pears. The fruit is small and misshapen with the surface covered in small craters and lumps. It is more common on very old trees. There is no cure and the tree should be uprooted and burned.

REVERSION

This virus disease, which is found mostly on Blackcurrants, causes a change in leaf shape and the leaf buds to become red. It is spread by the Big Bud Mite and once infected, the plants slowly get worse. There is no cure and affected plants should be dug up and burned.

ROOT ROT

Usually a sign of over watering and poor drainage. If possible, repot into fresh compost to encourage new root growth and regulate watering.

RUSSETING

On a few varieties of Apples this is normal and how they get their name but it sometimes occurs on varieties that it shouldn't and causes the fruit to be unsightly. The eating quality is not affected and the cause is put down to poor growing weather.

SCAB (APPLES)

This affects Apples and Pears and causes brown marks on leaves and fruit. Use a Bupirimate and Triforine based spray and treat when the flower buds are formed but tightly closed and again when they have turned pink. Spray a third time when the petals have fallen.

SHOT HOLE DISEASE

This is a fungal disease that affects Plums, Peaches and Cherries and causes small holes to appear in the leaves. Only weak trees are affected and if the tree is well fed, should not occur

SILVER LEAF

A serious disease of Plum trees, which can also affect Apples, Cherries and Peaches. The leaves have a silver sheen on them turn brown and drop off the tree. Dieback of shoots occurs and when the wood is cut into, a black ring can be seen. Cut out all dead branches below the level of infection and paint all wounds with Arbrex. In extremely severe cases, toadstools will appear at the base of the tree. If this happens, the tree will have to be dug out and burned.

SILVER LEAF (FALSE)

This looks like silver leaf at first glance with all the leaves turning silver. If the wood is cut there will not be the distinctive black ring of true silver leaf. This is caused by a lack of water. Put down a thick mulch in spring and keep well watered.

SPUR BLIGHT

Purple patches appear around the buds on Raspberries and Loganberries. These patches turn silver and the buds die. Cut out and burn infected canes and spray with fungicide.

STRAWBERRY MILDEW

This is a common disease of Strawberries and causes dark patches to appear on the upper surface of the leaves with a silvery grey mould on the underside. The fruit can also be affected. Spray with a fungicide at the beginning of flowering until the fruit starts to colour. Remove and burn all foliage after harvesting.

TOMATO LEAF MOULD

The tops of the leaves turn yellow and the undersides form purplish brown patches. Prevent by having a good airflow around the plants. Remove any infected leaves and spray the plant with a fungicide.

VERTICILLIUM WILT

More usual on Tomatoes. The plants wither in hot weather and pick up at night. Leaves turn yellow and brown streaks run through the stems. Spray the plants and soil with a fungicide and mulch around the stems so that new roots can form. Avoid growing Tomatoes in the same soil for at least 2 years.

VIRUS (fruit)

This usually shows as a yellowing mottling of the leaves. There is no cure. Prevent infection by controlling the aphids that carry the infection. In mild cases, cut out the infected area or branch.

Flowers

BLACK SPOT

This disease of Roses causes black spots on the leaves. Regular spraying with a fungicide from spring onwards will help prevent it.

FOOT AND ROOT ROTS

This fungus disease causes the base of the stem of plants to go black and shrink. Water with a copper fungicide at the first signs.

LEAF SPOTS

These come in all shapes and sizes, from brown to red spots. They are fairly difficult to control but a regular spray with fungicide will help.

NUTRIENT DEFICIENCY

An abnormal change in leaf colour usually indicates a deficiency in an essential nutrient. Ensure that the tree is well fertilised.

PETAL BLIGHT

Not serious but can spoil blooms that are intended for showing. Causes small water filled lumps on the petals. Spray with Myclobutanil at weekly intervals.

POWDERY MILDEW

Caused by dry conditions. Spray with fungicide at first signs.

RUST

A serious disease that attacks Roses and many herbaceous plants. It causes reddish brown spots on the underside of the leaves. It is extremely difficult to control but spraying once a fortnight with Myclobutanil will help. Some varieties of plants are less prone to attack and it is advisable to plant these.

TUBER ROT

Attacks mainly Dahlias that are in storage and causes the tubers to go soft and brown. Cut out infected areas and treat with Sulphur.

VIRUS DISEASES

These show up in various forms, some of which do no damage at all but are used to form variegated versions of plants. Other forms leave the leaves yellow, streaked, spotted, crumpled or stunted. If it is detrimental to the plant it will have to be dug up and disposed off. Regular spraying against insects can prevent it occurring.