Biological Control

For plant diseases, biological control is most usually defined as direct or indirect inhibition of a disease, or the pathogen causing the disease, by another organism (antagonist) or group of organisms. The beneficial organism is termed the biological control agent. A broader definition also includes specialized metabolites, isolated, for example, from interactions or plant extracts that can be useful for controlling diseases. These include substances with signalling, antibiotic or attractant activities (e.g., pheromones), and are often termed biopesticides. However, we recommend that the misleading term biopesticides is avoided and the new term bioprotectants is used. Thus, the term bioprotection should replace the wider use of the term biological control mentioned above, and include the use of non-living extracts and natural products as well as the more narrowly defined biological control; thus, the term biological control can be reserved for situations where a living BCA is applied.

Classical BCAs are defined as natural enemies that self-propagate and establish in the environment to which they are introduced to suppress pest populations. Augmentative BCAs are not expected to establish and are defined as mass-produced natural enemies that are periodically introduced into a specific environment to suppress pest—and pathogen—populations. Augmentative BCAs can be further subdivided into seasonal inoculative agents, which can reproduce and persist throughout the growing season, and inundative agents, which cannot reproduce and must be reapplied frequently throughout the growing season.

Benefits of Biological Control

Biological control is seen to offer several opportunities for improved disease control, especially where conventional approaches are limited or compromised. Alongside the use of disease-resistant cultivars, biological control is seen to have an important role in integrated pest management strategies aimed at reducing the use of chemical pesticides. A BCA is an organism or collection of organisms rather than a chemical per se. It is likely to be more specific in effect than most commercialized agrochemicals and less likely to leave potentially harmful residues in the environment. A living organism may be able to penetrate the diseased plant or affect the target pathogen in a way that a chemical cannot. In addition, in some situations, the risk of the evolution of pathogens resistant to a chemical pesticide is greatly reduced by applying a BCA. Biological control is also publicly perceived as natural and therefore less environmentally harmful than chemical control; in many cases this is true, because no completely novel molecule is being introduced to the environment. Because of these favourable perceptions, many forms of biological control are also accepted for use in organic cultivation. It is also claimed that—again only in some cases—a BCA may be cheaper than a pesticide.