PLANTS are a source of food for many types of insects and other small creatures, and there are few plants which are not attacked by them. In some cases the attacks may be sporadic and unpredictable, but most of the more serious pest attacks can be expected to cause damage to certain plants year after year. The severity of the attacks usually depends on the weather conditions of the current and previous seasons. A mild, wet autumn is often followed by a severe infestation of leatherjackets in the spring, and hot weather is ideal for the multiplication of greenfly and other aphids.
The variation in the range of pests found in different localities is probably due to the climate, but is also influenced by the amount offrom the weather, the type of and the kind of vegetation growing near the garden.
No single garden is therefore likely to harbour all the pests mentioned in this section, and preventive measures should only be taken if pests are known to be present and they are causing appreciable damage to plants.
It is wise to learn to recognize the more common types of pest feeding on the plants, and, during a few years of experience, to build up a general idea of the degree of damage caused by those which occur regularly.
Pests can usually be divided roughly into three categories:
(a) those which cause so little damage that control is unnecessary;
(b) those which normally cause little damage but are liable to increase under certain conditions, such as hot weather, rain, etc. Keep these pests under observation and deal with them if they show signs of increasing;
(c) those which cause severe damage every year. If possible take preventive measures before they appear, or destroy them as soon as they are seen. If these points are kept in mind pesticides need not be used unnecessarily and the beneficial insects, of which there are large numbers, will have a chance to exert a natural control over the pests.
There are a great many pesticides available and each one may be sold under a variety of trade names. Make sure that any pesticide bought bears on the label the mark of the Agricultural Chemicals Approval Scheme which is operated by the Ministry of Agriculture, Fisheries and Food. The labels of approved products will also indicate which pests are controlled by the pesticide and which plants are adversely affected by the chemical.
USING A PESTICIDE
1. Before using a pesticide read the instructions carefully.
2. Do not use more pesticide than is recommended or the plants may be damaged.
3. Spray during dull weather or in the evening as damage can be caused by spraying in bright sunshine.
4. Avoid spraying open flowers, to safe-guard bees and other pollinating in-sects.
5. Do not spray in windy weather when the spray might drift to open blooms or to fruit and vegetables ready for picking.
6. Most pesticides are poisonous to human beings and it is unwise therefore to smoke or eat while applying them. They are also poisonous to domestic animals.
7. After spraying, store all pesticides out of reach of children, wash out the utensils used and wash the hands thoroughly.
Allow three weeks to elapse between the spraying and harvesting of edible plants sprayed with aldrin and dieldrin. For plants sprayed with D.D.T., B.H.C. And lindane allow two weeks, for those sprayed with malathion one week, and for those sprayed with nicotine two days. Derris is non-poisonous to human beings but, as with the other materials recommended, do not use it near ponds containing fish.
The information in the following pages will enable the gardener to recognize and deal with the more important and troublesome.
It is impossible to include all the pests which may be found; should any of the less common pests suddenly appear in larger numbers than usual, help can be obtained from the advisory services of the gardening press or insecticide manufacturers.