Greenhouse Pest and Disease Control
Greenhouse Pest and Disease Control
In the warmth and humidity of the greenhouse, pests can quickly build up numbers, and diseases develop rapidly. Thus, it is essential to keep a close regular watch on your plants and catch any problem before it gets out of hand.
It is also important to identify correctly what is causing the trouble. Sometimes the symptoms of a deficiency or disorder or even a pest attack look more like those of a disease. For example, a sooty mould can be formed on the sticky secretion exuded by aphids hidden under the leaves, so the aphids are the real culprits.
Only when you understand a problem will you be able to decide upon which course of action to take to check it and, equally important, to avoid it happening again in the future. Therefore, the emphasis of this section of the site is upon preventing problems. The pests, diseases, and disorders described in detail are ones which are found only in the greenhouse or which are more troublesome there than outside.
First, it is important to select the right plants, matching them to the conditions in the greenhouse. If they are struggling to survive, then they will be very susceptible to. Remember that it is not only temperature that affects them, but factors such as the amount of light, the humidity, and day length. For example, avoid winter crops in a greenhouse that is in shadow when the sun is low in the sky, as they will be weak and lank. Stick to green manures and hardy instead.
Pests and diseases will get out of hand more easily if you grow only one type of plant, whether it is tomatoes or. Having a mixture of plants — ones from different plant families, and perennials, bushy ones, and ones which trail and climb — makes it more difficult for problems to spread and more likely that pests will be controlled by natural enemies.
Encouraging natural predators
Many greenhouse pests have natural predators which will find their way in through the vents and door provided that the conditions inside are not extreme.
The first step is to encourage these creatures into the garden. Hoverflies, whose larvae prey on aphids, are attracted by simple open colourful flowers which give them an easy feed of nectar. Grow lots of these in the garden and try planting a few in the greenhouse too. Frogs can be encouraged by having a pond in the garden. They will consume large quantities of slugs, reducing the likelihood of these pests coming into the greenhouse, and you may even find that a frog will come to live amongst the damp cool foliage of plants under the staging.
It is also important to be able to distinguish your friends from your enemies. For example, do notthe ground beetles which scuttle away when you move a big pot, as they also prey on slugs.
Greenhouse pests such as whitefly, mealybug, and scale insects rarely find their own way into the greenhouse — it is humans that take them there on plants. Always examine any new plants carefully before putting them in the greenhouse, and keep them in quarantine until you have dealt with any problems.
Many breeding programmes are now aimed at finding vegetable varieties which are less susceptible to specific pests and diseases. The individual crop entries indicate which problems might be avoided by growing such resistant varieties. Keep a look out in the seed catalogues and at nurseries as new ones are being introduced all the time.
Once you have planted up your greenhouse, success depends upon good management — careful watering, sufficient ventilation, attention to hygiene, and correct feeding. Plants whose basic diet comes from, manures, and organic fertilizers rather than from chemicals and liquid feeds will not be so prone to deficiencies or disorders, and they are less likely to produce the lush sappy growth that attracts pests and encourages diseases.
Crops belonging to the same plant family should not be grown in the same place in the greenhouse border year after year, as this can cause the build- up of-borne pests and diseases. Root rots and eelworms, for example, are common problems in greenhouses where tomatoes are always the main crop. Peppers and aubergines belong to the same plant family, Solanaceae, as tomatoes, and therefore are prone to many of the same problems. However, you could follow tomatoes with or melons. A possible three-year rotation for one border could be:
Year 1 Tomatoes, peppers, and aubergines.
Year 2 Cucumbers and melons.
Year 3 Strawberries and, followed by early winter salad crops.
For a small greenhouse where a rotation is not practical, changing the border soil is an effective if exhausting alternative. In autumn or spring, remove the soil to the depth reached by the plant roots and replace it with good soil from the garden, which has not recently been used to grow similar crops. Do this every two or three years as a precaution, even if you have not seen signs of trouble.