Tomatoes are one of the most popular vegetable crops, but they can suffer from attack by a number of garden pests such as aphids or red spider mite and diseases like tomato blight or fungal infections and viruses. These can affect the quality of the tomato fruit or reduce the yield, and in the worst case the plant may die. Prevention is better than cure and healthy tomato plants grown in the right conditions are likely to escape most tomato pests and diseases. If an attack does occur, early recognition and treatment can normally prevent significant damage to tomato plants and crops.
Growing Healthy Tomatoes
Prevention is better than cure. Minimise the risk of tomato diseases and pest attack by:
- Always using fresh compost for growing tomatoes. If planting in open ground, try to avoid planting in soil which has been used for tomatoes before.
- If reusing pots or containers, wash and sterilise them with a solution of Jeyes fluid or similar disinfectant.
- Scrupulous cleanliness of greenhouses, and annual fumigation against pests and diseases.
- Making sure that contaminated plants and material are never taken into greenhouses.
- Selecting bought in plants carefully. Choose sturdy, compact plants with dark green leaves. Avoid any plant which is leggy or shows any sign of stress.
- Watering regularly, but ensure good drainage to ensure the compost or soil is always moist but never waterlogged. Irregular watering will damage the fruit .and make plants more vulnerable to disease.
- Removing prunings and any yellow leaves immediately.
- Keeping greenhouses well ventilated.
Garden Pests Attacking Tomato Plants
The common garden pests which may attack tomatoes are:
- Aphids. Greenfly or other aphids are sap-sucking wingless insects which may attack young shoots, concentrating in masses on growing tips and stunting growth.
- Eelworms. These minute worms burrow through the tissue of plants, causing discolouration and distortion of leaves and flowers. Avoid by scrupulous cleanliness and only using fresh soil or compost. There is no effective treatment. Affected plants should immediately be removed and destroyed.
- Red Spider Mite. Minute red spiders, more likely on tomato plants grown under glass. Leaves appear mottled, then may show a bronze discolouration. In more severe attacks plants may be choked with cobwebs. Avoid by keeping plants well watered and maintaining greenhouse humidity.
- Whitefly. Tiny white flying insects which congregate on the underside of the leaves of tomato plants grown under glass, which are coated with honeydew and sooty mould. In severe attacks the flies fly up in clouds when plants are disturbed.
Treating Insect Pests On Tomatoes
EU legislation has banned an increasing number of traditional chemical remedies such as Derris and Malathion, resulting in an ever reducing and fast changing range of garden insecticides in garden centres.
Currently, proprietary insecticdes such as Bayer’s Sprayday Greenfly Killer Plus and Doff’s All-In-One Bug Spray claim to be effective against aphids, red spider mite and whiteflies. Take care to follow the manufacturers’ directions, particularly in respect of the interval between spraying and harvesting.
Organic remedies include:
- Spraying plants with insecticidal soap solution.
- Setting sticky fly traps or gently vacuuming plants to remove whitefly.
- Brushing off or crushing small groups of aphids on first sighting.
Diseases and Disorders In Tomatoes
Tomato plants grown in healthy conditions will generally resist diseases, but the following may occur:
- Blight. Potato and tomato blight cause greyish brown spots on the leaves of outdoor-grown tomatoes, and brown marbled areas can make the fruit inedible. Reduce the risk by stringent plant hygiene. Spray with Bordeaux mixture.
- Fusarium Wilt. Root infection in outdoor tomato plants caused by infected soil or compost. Plants die back to the ground. No cure. Remove and destroy all infected plants.
- Greenhouse Wilt. No cure. Reduce risk by maintaining temperature above 25 degrees centigrade, and misting leaves. Destroy infected plants and discard compost or soil.
- Leaf Mould. Upper surfaces of leaves show yellow patches, developing into grey brown fluffy growth. Remove and destroy discoloured leaves and treat plants with a fungicide such as Bordeaux mixture.
- Fruit Damage. Dark brown or black rings on the fruit and split fruit are both caused by irregular watering.
More About Growing Tomatoes
Growing your own tomatoes.
Growing tomatoes in growbags and containers.
Choosing which varieties of tomatoes to grow.