Pests: a stitch in time

After a severe winter we may have become complacent about summer pests. Bollworms, for example, do not appear regularly – and herein lies the danger. We just don’t notice these night-flying moths until it is too late. Researchers using ultraviolet lights at night to monitor pest cycles find that many pests appear suddenly and then disappear again. This phenomenon is linked to weather conditions and the effect of natural enemies on population numbers. Certain pests are difficult to predict. When a particular insect population increases, so do its natural enemies – until they devour all the insects and run out of food, when they decline again in a seesaw effect. Other pests, like diamondback moths in brassicas, build up slowly and so shouldn’t catch you by surprise. Flying moth, hidden bollworm Bollworm moths lay single eggs near the edge of young cabbage leaves. After hatching the caterpillars usually hide under the leaves, where they consume your crop protected from predators and crop chemicals. They must be controlled before they reach this stage. T he same happens with lettuce. If caterpillars are around when the leaves start to form a head, it is usually too late. Check thoroughly for pests before the heads start to form. Pheromone traps give early warning F ortunately, there are now pheromone traps that alert you when bollworm moths are active. Some farmers even find that with enough of these traps they can virtually control the pest. Unfortunately, the trap only attracts male moths, and mated females will still lay sufficient eggs to cause a problem. The main advantage of the trap is the advance warning it gives, enabling you to kill off the newly-hatched larvae. Pheromone traps can save you a lot of money, as you only need to spray when moths are present. Move away from toxic pesticides Although there is a worldwide move away from pesticides towards safer products, some of these less toxic pesticides are not as effective in controlling older caterpillars, making it crucial to apply the product in time to kill hatchlings. Vigilance is important W ith these traps you can get an accurate idea of certain pest infestations. However, farmers will have to learn more about their pests and how to identify the relevant moths. Get into the habit of checking for moths when walking through your land and around the outside lights at night. – Bill Kerr ([email protected] or (016) 366 0616. |fw