For most people the word 'pest' conjures up a vision of hordes of greenfly on roses, whitefly on indoor plants, or blackfly on beans. I am not surprised, because all three are pests and they all tend to infest on an epidemic scale. But gardeners view any organism that interferes with crops as a pest, whether it be an insect, a virus or a predatory animal.
Now I am not going to say anything about viruses, or fungi, or bacteria, or animals like rabbits and moles and next-door's cat (not this month, anyway), but concentrate on insects and insect-like pests, which includes slugs and snails (which are both molluscs even if the slug doesn't have a shell) and eelworms (otherwise known as nematodes, some of which are not pests because they attack and kill things which are). Insects are the largest group of creatures on earth. In evolutionary terms they are highly successful, and have proved to be man's fiercest competitors. A state of conflict exists where man does his best to get rid of insects, and the insects bite back. Insects have caused more deaths to mankind than all wars put together. Insects will attack most plants, whether they live indoors in the house or the greenhouse or outdoors in the garden or in pots on the patio. Like all illnesses and disorders, prevention is better than cure and the best way to reduce your losses is to make sure that your plants are healthy when you plant them, and then look after them properly. Many physiological disorders of plants are caused by poor husbandry, such as giving them too little (or too much) water or too much (or too little) nitrogen fertilizer, and these pave the way for attack by pests. So be watchful, and as soon as you notice any signs of distress or damage, act promptly. Unfortunately, the pest itself may be almost invisible. Eelworms, for instance, are difficult to see under a microscope, yet their size bears no relation to the damage they can do. Even pests which are big enough to see may not always be sitting in full view. You will have to dig underground to find vine weevil grubs, or wait for night to catch such insidious creatures as slugs.
Pests which attack leaves and flowers are the most easily identified because the damage occurs rapidly and is usually quite recognizable. Two main groups of pests attack leaves: those which bite, like beetles, and those which suck, such as greenfly. They may hide inside or outside the leaves, or, like the notorious leaf-miner, burrow between in middle layers of leaf tissue. They may, like the tortrix moth caterpillar, tie two leaves together and hide in between them. Some of these pests are cunning little devils. Larger pests (like caterpillars) are usually more noticeable but they may attack and run (or fly) away, in which case you will have to spray or lay bait against the next visit. Fortunately there are many methods of control at your fingertips, providing you diagnose the enemy correctly and act as swiftly as you can. Knowing something about the life cycles and habits of pests can help in anticipating and preventing trouble. For instance, a major factor in determining how active they are is temperature; the warmer it becomes the busier they get. And, up to 35°C (95°F), they breed faster too. Day length also plays a part in controlling the breeding seasons and migration patterns of many insects. This is why they always become scarce in autumn, even before cold weather arrives. Clear away and burn garden refuse every autumn because it provides ideal shelter for overwintering pests. Many hide away as eggs, which can also be destroyed by the use of insecticides.
Insecticides kill in two main ways. Some act as a stomach poison when the pest either eats it with the leaf or sucks it up with the plant sap, while others will poison through the 'skin' or suffocate the pest. The method you choose depends on several factors, such as climate, type of insect and type of plant involved. Many early insecticides were non-systemic or 'knock-down' chemicals which killed either by blocking the breathing processes or by poisoning when absorbed through other exterior surfaces. But they do not persist for long and have to be used frequently in order to be effective. However, some are still very useful for certain purposes. Pyrethrum and derris, for example, are both very effective general insecticides. They are derived from plants (and can be classed as 'green') and do not persist for long. This means they are safe to use on vegetables even up to the day before harvesting. Derris, however, is harmful to fish so do not use it near fish ponds. The systemic insecticides are absorbed by the plant and dispersed throughout its entire system, and any biting or sucking insect will ingest them while feeding and be killed. These pest-killers remain in the plant for several days (sometimes even weeks) and they act against a wide variety of pests. But too often spraying can result in the development of pests that are resistant to them. So spray on sighting the enemy rather than 'just in case'. Most pesticides are sold under trade names, partly because the chemical names and formulae are cumbersome and difficult to remember. You can, however, be sure of getting what you want by reading the contents on the label and checking with the chemical, or proper name. Full chemical names are often abbreviated, for instance benzene hexachloride is known as BHC, or gamma-BHC. Theoretically you should always use protective clothing when using chemicals, which is very inconvenient if you only want to spray one or two plants. However, wearing rubber gloves is a very good idea, and don't forget to wash your hands and face thoroughly afterwards. Don't allow children or animals to be with you while you spray, and don't let them eat anything that has just been sprayed. Also wash out all spraying equipment after use - but not in the kitchen sink.
In some cases you may be able to use physical methods of combat, such as picking caterpillars off plants and burning them (the caterpillars, not the plants). This is always preferable to spraying, because all sprays have some adverse effect on plants. This is why you must adhere strictly to the manufacturer's recommended rate of application. There is one final thing I have to say about insecticides. Always read the label before you buy, and if in doubt, either ask or don't buy. And always obey the instructions. Never use a stronger solution than that recommended - it could kill the plant as well as the pest. And never, never, never put diluted chemicals into lemonade bottles, even if they are labelled. Young children who can't read can still recognize the bottle.
Happy Gardening,
written by Bill Hutchings
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