Insect Pests and Plant Diseases
Insect Pests and Plant Diseases
With pests, diseases and, the message must always be: Anticipate. Be prepared, Take precautions.
Check your plants in the very early stages, especially in spring when young plants are at risk.
Gardeners’ attitudes to controlling these problems vary. There are those who want pristine produce from their garden and will spray for every possible pest and disease, and there are those who are ‘anti chemical’ and are prepared to put up with scabby apples and perforated. Most people, however, will rely on cultural techniques to reduce the problems, only resorting to chemicals if and when things get out of hand.
There are several ways to lessen the problems caused by pests and diseases : Rotate your crops.
Start with strong healthy plants and grow them well.
Remove the source of the problem as soon as it occurs.
Create an environment that discourages the development of pest or disease.
Potatoes grown in the same piece of ground year after year will suffer from a build up of eelworm in the. Similarly, brassicas will not do well if grown in the same spot each year as their roots become infected and grotesque with club-root. To avoid soil-borne pests and diseases, the vegetable gardener can divide up the plot and rotate crops.
Always buy healthy fruit plants, ornamental trees and shrubs. When buying, look for obviously healthy and fresh material. Avoid wilting plants with dried up roots (unless you’re short of material for your heap). When raising your own plants from seed, only use fresh seed from a reputable source or, if saving your own, only keep seed from healthy plants and store it carefully. Some bought seed will have been `dressed’ with a chemical to prevent problems later on. When you should do everything you can to ensure rapid germination. In the glasshouse, seed should be shown thinly into sterile compost in clean trays. Warmth and moisture will encourage germination of many flower and vegetable seeds, but once through, lower the temperature and reduce the humidity to avoid soft growth. Avoid overwatering and too well-firmed compost as this combination leads to damping-off diseases. Prevention is far more effective than cure. Whether are of flowers or vegetables, do not overcrowd your plants as this sometimes results in poor growth and poorer air circulation which creates more problems.
Another way of stopping the spread of pests and diseases is to remove and destroy them as soon as they are spotted. For example, those white powdery tips of shoots on your apple tree should be cut off before the disease — powdery mildew — spreads. As the holes appear in yourleaves, find the culprits — caterpillars, and pick them off.
Plants won’t succumb to pests and disease if you create a healthy environment. For example, cabbages are less likely to get clubroot if the soil is not too acid and is well drained; and your strawberries or lettuces under cloches will not develop grey mould so easily if you provide good ventilation.
Waging War on Pests and Diseases by Other Means
Using chemicals is the only way to control certain problems. But only use them if you really have to, and then only sparingly, as they often have undesirable side effects, particularly if used carelessly. You might be quite happy, for instance, to spray your apple trees regularly with an anti-mildew fungicide. But that fungicide may reduce the viability of the pollen and so perhaps reduce your crop. Similarly, the insecticide you put on to kill a few greenfly may also kill their natural predators and parasites.
The use of predators to keep pests in check has been developed in recent years. In a controlled environment, like a glasshouse, predators can reduce a number of pests that are otherwise difficult to control, even chemically. A good example is whitefly which affects many glasshouse crops. A few small wasps, however, will reduce the whitefly population and prevent further serious damage.
This biological control is not so well developed outside the greenhouse, although gardeners can encourage natural predators to keep certain pests down. Birds like tits, for instance, should be encouraged for they will search out codling moth larvae which otherwise tunnel into your prize apples.
But birds are often pests in themselves — and one of the most difficult to control. How can we keep them off our valuable crops? Bird scarers, of course, but none of them work for long. The worst offenders in the garden are pigeons and bullfinches in winter, and starlings, thrushes, blackbirds and sparrows during the summer. When food is short in the depths of winter, pigeons will turn to the brassicas, especially early in the mornings. The only really effective way of keeping them off is to protect the crop with plastic pigeon netting either draped over the crop or supported on posts. Pigeon netting has large holes allowing snow to go through, so the risk of the whole lot collapsing under heavy snowfall is minimal. Bullfinches are the other winter pest, often creating havoc after Christmas when supplies of seeds become scarce. Their diet changes to swelling buds of forsythia, gooseberries, pears and plums as well as other fruits.
Young vegetable seedlings can be protected by a single strand of strong black cotton along the row about 5cm (2in) above ground level. Draping trees or bushes with black cotton can be effective, but only use cotton that breaks easily as the stronger synthetic threads will maim the birds. Far better to protect your fruit or shrubs with netting. You may prefer to grow all your fruit in a fruit cage, but draping netting over the plants is just as effective, and preferable for flowering shrubs that only need very temporary protection. The mesh size needs to be about 25mm (1in) and this will also do to protect your fruits from starlings, blackbirds and thrushes in the summer. I also use the same netting, supported on wire hoops from my low polythene tunnels, to keep sparrows off seedlings. Finally, in an attempt to blend in with the surroundings, most garden netting is made in a lurid, bright green. If you have a choice, buy black.