Microbial antagonists can suppress plant pathogens by producing antibiotics or by means of competition—producing larger populations, and thus occupying and competing for the same ecological niche. A competitor will challenge the pathogen for infection sites, nourishment, or other resources and, in the process, reduce the population size of the plant pathogen. Microbial antagonists can produce toxins active against arthropods, plant pathogens, or weeds, or compete with plant pathogens for nutrients or preferred sites on plant surfaces. Mild strains of plant pathogens that cause little or no disease can induce resistance responses in the plant or otherwise provide protection from disease.
Genes or gene products derived from living organisms that kill, disable, or otherwise regulate the behavior of plant pests are biological-control products. Examples include the Bacillus thuringiensis (Bt) toxin, delivered by a killed microbe, and pheromones or other semiochemicals used to kill or disrupt the reproduction of arthropod pests.
It must be noted that genes or gene products are derived from living organisms, but they are not inherently more suitable supplements than synthetic products. Indeed, certain synthetic products can be less detrimental to environmental balances than some products derived from organisms; some natural plant products used to formulate botanical insecticides such as rotenone and pyrethrum have broad-spectrum activity and can be highly toxic to beneficial organisms. It is the spectrum and activity of products used in ecologically based pest management that are of primary importance rather than the source of the products. The most useful biological-control products are those that have minimal impact on all components of the agroecosystem—except for the target pest.
Narrow-spectrum synthetic pesticides that meet the criteria of safety, profitability, and durability are suitable supplements for EBPM. For example, the synthetic insecticide pirimicarb is highly selective for one group of pest arthropods, aphids, and does not adversely affect most biological-control organisms.
Plants that have developed resistance against pests will be important components of EBPM. Plant breeders have successfully identified and deployed genes for disease and arthropod resistance in numerous crops; in the future, molecular genetic methods will become more important as a means to producing pest-resistant plants. At present, resistance is the predominant defense against many plant diseases, such as rust diseases, that would otherwise severely limit cereal