Biological Control, Integrated Pest Management (IPM), and other environmentally-friendly control methods
Biological control involves the use of a pest’s own natural enemies (parasites, predators and pathogens) – whether introduced or otherwise manipulated – to suppress the pest populations to an acceptable level. The word “pest” is used here in a broad sense, which includes diseases, insects, mites, nematodes and weeds and/or invasive alien plants.
While in principle there is little difference between the biological control of diseases, insect pests and weeds, it is usually accepted that a far higher degree of host-specificity is required for a weed-biocontrol agent than for a pest-biocontrol agent. Most pest-biocontrol agents kill their host directly, while suppression of weeds could take place by killing or weakening the weed, by reducing its reproductive capacity, or by creating an avenue for infection by pathogens.
Different techniques can be used in biological control:
- The technique most often used for the control of insect pests and weeds is referred to as classical biological control. It involves the introduction of natural enemies from the native range of the pest or weed from its country of origin, after which the natural enemies become established in the new country, build up their numbers and remain present in the new environment.
- Inundative biological control involves the repeated introduction and release of large numbers of natural enemies.
- Augmentative biological control describes actions that increase the populations of natural enemies.
- Conservation biological control refers to environmental modification to protect and enhance natural enemies.
Biological control cannot be expected to solve all pest or weed problems in a particular situation, but should nevertheless be the core around which pest or weed management systems are built. Biological control is often only possible within the framework of an integrated pest management (IPM) system.
2. Why the need for an alternative?
Pesticides have revolutionised agriculture, increasing yield and improving harvest quality, but their leftover stockpiles can contaminate the environment and endanger human health. If a pesticide has the potential to kill, then it also carries a risk to the environment. Some pesticides are harmful to people and the environment because they remain in the soil, air and water for a long time, are easily dispersed by water and air, and concentrate in the high-altitude, low-temperature regions.
Irresponsible use of non-selective pesticides eliminates not only the target pest but also many beneficial organisms that play an important role in garden, crop or natural ecosystems. Some of the answers to our pest problems may be right under our noses, such as the tiniest microbe in the soil, a fungus, bacterium, virus or nematode or one of the many parasitic or predatory insects, reptiles, birds and mammals in our environment. Organisms that we might consider “pests” have a place in the scheme of things. Without them there would be none of the wonderful birds, spiders and reptiles on our farms.
Programmes which promote the responsible use and disposal of agricultural chemicals are run by CropLife SA and CropLife International (see the “Chemicals in agriculture” chapter).
3. Biological control of agricultural pests using predators and parasites (including IPM)
Biological control of agricultural pests usually forms part of an integrated pest management (IPM) programme. IPM refers to the ‘integration of two or more control strategies’ for suppression of the pest below a given threshold level. Many purely chemical strategies are also aimed at reducing pest populations below a threshold level and not at eliminating entire populations of the pest. IPM is based on the assumption that it is not necessary or cost effective to try to eliminate an entire population of pests.
Instead, threshold levels are established to determine when control is necessary to bring pest population levels down. When the number of pests reaches a threshold level, a pesticide may be used to prevent excessive crop damage or loss greater than the cost of preventing the damage. IPM programmes require a thorough understanding of various techniques such as biological, cultural, mechanical and chemical control methods. Some actions needed in support of integrated pest management include correct pest identification, pest monitoring, and determination of economic injury levels.
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