Early in this century, plant pathologists recognized that (a) both native and exotic microorganisms could suppress plant diseases; (b) disease suppression could be manipulated through the use of cultural and management practices that altered soil's organic matter, temperature, or pH; and (c) disease suppression was attributed to the presence of suppressive microorganisms (Cook and Baker, 1983). The first attempts to suppress plant diseases by introducing beneficial microorganisms to soil were done in the 1920s (Cook and Baker, 1983), and the fungus Phlebia gigantea, the first biological-control organism used commercially for control of an aerial plant disease, was described in the 1950s. In addition, inoculation of cut pine stumps with P. gigantea prevents infection of the stumps by the pathogenic fungus Heterobasidion annosum and its subsequent spread to neighboring standing trees through root grafts. This biological control is still widely used today in commercial pine plantations in England and Sweden. Inoculation of chestnut trees with hypovirulent isolates of the chestnut blight pathogen Cryphonectria parasitica was initiated in France in the 1960s, where it successfully suppressed chestnut blight in many regions. Biological control of crown gall with the bacterium Agrobacterium radiobacter strain K84, which was initiated in the 1970s, is now used to suppress the disease in orchards and nursery stock worldwide. Today, at least 30 different biological-control organisms are available as commercial formulations for suppression of plant diseases (Lumsden et al., 1995).
As early as 1922 the United Fruit Company identified land types in Central America in which banana plants were termed either short-lived or long-lived crops. Both were grown in soil containing wilt pathogens, but only the long-lived plants survived because they were planted in soil that suppressed the pathogen Fusarium oxysporum (Cook, 1990). Since then, this natural process of suppression of fusarium wilt has been demonstrated for carnation, cucumber, cotton, flax, muskmelon, and tomato crops.
In the 1930s, knowledge of medicinal antibiotics was applied to plant pathogens by Weindling, a plant pathologist, who researched the use of Gliocladium and Trichoderma fungi for their antibiotic effects on damping-off disease. In 1938 Linford and colleagues reported on the use of a nematode-parasitic fungus to control root-knot nematodes (Cook, 1990). The knowledge gained by these applications of biological controls continues to be used today in managing plant pathogens, weeds, and arthropods.
Early agriculturalists realized the benefits of cultural practices such as rotating crops, altering planting and harvesting schedules, planting mixtures of crops, managing irrigation and drainage, and removal of crop residues, to reduce pest