Controls and Treatments for Vegetable Pests and Diseases
With good cultivation and careful management of the soil, you should be able to ensure that crops are strong and healthy. Plants which always have the food and water they need are seldom badly infected with disease or attacked by pests and are often not infested at all. Plants which have become weak are the main targets and an epidemic is generally a sign that you have not supplied or ensured the right growing conditions.
What is known as ‘garden hygiene’ is important. It means keepingclear of piles of various objects: bricks, stones, corrugated iron and wire netting, pots and boxes, twigs and branches, polythene sheet and so on, all of which provide homes and shelter for small and large pests, such as mice, and insects, and for sources of infectious diseases.
Many weeds are alternative hosts for these troubles; the remains of roots left in the ground can also be the starting point for infestations, so canand protection. If you have concrete , keep them free of soil; keep mown and gravel paths clear of weeds.
When you are buying new stock, order from nurseries or garden centres which supply plants certified free of disease (where there are certification schemes in force for a particular species) – and which have a good national reputation. Tempting though it is, don’t accept otters of plants from friends unless you know the plants to be clear of diseases; they are so often infected, in particular with virus, which may not be apparent.
Various ‘biological’ methods of control are beginning to be available to gardeners, for the control of red spider mite andso that chemicals do not have to be used. There are also many predatory insects naturally present in the garden; are a well-known example.- By not using chemicals or by using those specific to the pest, these beneficial insects will survive and help to keep down the marauders of your crops.
If you do have to resort to chemicals, there are some modern kinds which are particularly safe and effective. Bioresmethrin is one of these, similar to pyrethrum, but even better and safer. Another safe but older one is derris; it needs to be used fairly frequently for best effects. Remember that it is a fish poison, and keep well away from ornamental ponds. Malathion is still the safest and least persistent of the phosphorus insecticides, but bioresmethrin seems likely to take its place. Benomyl is a systemic fungicide which will control(Botryis cinerea) and ; however, it is a worm killer, and it seems that these diseases are becoming resistant to it, so we may have to return to sulphur and copper. Diazinon is a useful soil insecticide which breaks down very quickly. Methiocarb is the best of the snail and slug killers if you are desperate, but there are other, safer ways of dealing with these pests if you must kill them.
There are various other chemicals which may need to be occasionally but in general, you should be able to sidestep their use by cultural methods of control, hand picking of pests and the use of natural. In any case, there is usually too much crop and the occasional nibble or scar on some of it is nothing to lose sleep about.
If, early in yourcareer, you need to sterilize soil, before you have got it into good condition, there is a widely available liquid sterilizer called formalin which will kill pests, fungal and bacterial diseases and weed-seeds. It is diluted with water in a 1: 49 ratio and is then given off as a gas when mixed with soil. Treated soil should not be used for planting until all smell has left it; this will take between two and six weeks. The solution is unpleasant to use, as it is irritating to the eyes, nose and throat. Full instructions for use are provided on the container.
Sometimes themay need a thorough cleaning out by fumigation, using sulphur candles. These, when lit, give off sulphur dioxide gas, which will kill fungal diseases and red spider mite. The greenhouse should be tightly sealed, and is best treated overnight. Both this and formalin are poisonous to warm-blooded animals and must be used with great care. Always keep all pesticides out of the way of children and household animals and wash out all containers and sprayers thoroughly after use.
There are various kinds of plant troubles: insect pests and fungus diseases (which are likely to cause the most trouble), bacteria, viruses, nutrient deficiencies, weather damage and attacks by small mammals (mice, voles, squirrels, rabbits, coypu) and birds.
The main insect pests, fungus diseases, and harmful mammals and birds are detailed in the list of Pests and Diseases Affecting the Kitchen Garden. Of the remainder, the symptoms of bacterial infection are usually a liquid, unpleasant-smelling rot and black or brown discoloration. Root crops in store, and occasionally , are most likely to be troubled and are best destroyed. Viruses infect the nucleus of the plant cell and any chemical which would destroy them would also destroy the plant. Infected plants must be completely lifted and destroyed as soon as seen, so that healthy plants remain healthy. Viruses are mostly spread by the feeding of sucking insect pests, especially greenfly. Symptoms of virus diseases may be yellow discoloration of the leaves, stunted and slow growth, malformation of leaves and flowers and little or no crop.
Nutrient deficiencies rarely occur in the average garden; lack of nitrogen is one of the few that may be apparent in plants growing in quick-draining soils. Lack of iron and lack of magnesium may show in alkaline soils; symptoms are yellow-to-white discoloration of the young leaves, for iron, or yellowing between the veins and later of the whole leaf, in the older leaves, for magnesium. These are the most likely nutrient deficiencies but, provided you manage the soil as advised, you should not run into this kind of trouble.
The weather is always with us and some damage to plants will occur which is unavoidable. Hail pitting of leaves and fruits, tearing and breaking, blackening and browning of leaves by wind is typical. Cracking and splitting of fruits, roots and tubers due to irregular supplies of water is another type of damage, when heavy rain or watering follows a dry period. Scorch of seedlings and scalding (browning) of tomato leaves and grape fruits by too hot sun can be prevented by shading. Blackening offlower centres by frost can be warded off with coverings on cold nights.
Eating of bark, nibbling of stored crops, attacks onand , removal of by mice and squirrels, and damage from birds, especially pigeons, sparrows, bullfinches and blackbirds, on , the onion family, bush fruit buds, fruit generally and , can all be warded off with netting draped securely above and round the plants.