15:20 - 08 July 2011
Greenhouse tomatoes are probably the most widely grown domestic greenhouse crop and the taste of homegrown tomatoes far surpasses anything you can buy in the shops. But tomato plants can be sometimes be high maintenance and are also susceptible to a variety of pests, diseases and other problems.
Many of the problems that occur in tomatoes are not initially caused by pests and diseases, but may simply be the result of the way that you care for and tend your plants. These problems are referred to as physiological problems and are often associated with nutrient deficiencies and can show up as mottled or yellowing leaves.
To get the very best results you need to provide the ideal growing conditions. This means everything from using the right growing medium to regular food and water.
Plants that are deficient in certain trace elements display symptomatic problems such as chlorotic leaves, split fruit, green patches and blossom end rot. Almost all of these are avoidable with proper care and attention, which means the right compost and the very best in plant fertilisers. A proper watering regime is essential, especially when the fruit have set, irregular watering can lead to split fruit and may also encourage red spider mite in the greenhouse. Fruiting plants will need a good long drink especially in hot weather, keep the water off the leaves and soak the compost thoroughly.
When plants become stressed and lacking in certain essential elements they are less able to perform to their full potential and quickly become susceptible to all kinds of pests and diseases. Sap suckers such as aphids and whitefly are common tomato pest and a menace indoors and out and can affect tomatoes.
When growing edible crops such as tomatoes it is essential to ensure that any pest controls you use are approved for use on fruit and vegetables. Ideally act before the problem gets out of hand. Greenhouse whitefly is one of the trickiest pests to control. Keep a look out for it by installing yellow sticky traps at the plant growth tips that will trap flying pests for identification purposes. Whitefly can be deterred from a greenhouse by growing French marigolds (Tagetes) within the greenhouse. It is the scent of these plants that is said to deter the pest. This is most effective if the Tagetes are grown with the tomatoes. Once you have greenhouse whitefly bringing in Tagetes plants may be too little too late. At this point you need to either employ a pesticide approved for whitefly control, but bear in mind that many greenhouse whitefly are now resistant, or if you are an organic or natural grower you can employ a biological control to target this pest.
The tomato moth, which lays its eggs in the foliage, can also affect greenhouse tomatoes and the fat green caterpillars munch on the leaves. Red spider mite can also be a problem, especially in very hot dry weather. Slugs and snails can also feast on leaves, stem and even developing fruit.
There are one or two fungal diseases that can affect tomatoes including tomato leaf mould that causes purple brown patches on the underside of leaves and yellow patches above. This is generally the result of too much warmth and humidity and usually occurs on greenhouse tomatoes. Remove and destroy affected leaves.
The worst fungal disease on tomatoes is blight, which when present attacks potatoes and tomatoes with great speed. It starts off as brown spots on the leaves and rapidly spreads throughout the plant causing the stems to collapse, the fruit to go black and to be completely unusable. It was this disease that caused the potato famine that left millions of people starving in the 19th century. There is still no effective control. Affected plants should be uprooted and destroyed. For future tomato crops choose to grow varieties, which show resistance to these problems and grow your tomatoes in a greenhouse where they are less likely to be affected by the spores. To be safe employ a greenhouse smoke over the winter to kill off any overwintering pests and diseases.
