Competition and antibioses are two of the ways biocontrol agents can help control plant pests.
“Producers are familiar with the concept of competition, as in crowding out weeds in a field using row spacing, stand density, etc.,” said Dustin Morton, commercial horticulture specialist, at the Alberta Ag-Info Centre in Stettler.
“Biocontrol agents can also be used as competition. This could include using Pseudomonas bacteria to block potential entryways for fireblight in fruit crops or Bacillus subtilis to outcompete powdery mildew.”
These micro-organisms don’t attack or infect the pest itself, their presence can be enough to deter other more problematic species, he said.
“Alternatively, these agents might infect the plant of concern, inducing a defence response that allows the plant to fend off an attack from another more dangerous pathogen or insect.”
Another method biocontrol agents use to help control plant pests is known as antibiosis or antagonistic association. In this case a biocontrol agent “runs interference with a pest.”
“Perhaps the best-known example is Bacillus thuringiensis, or Bt, which paralyzes the mid-gut when ingested by the larvae of Lepidopteran insects such as cabbage worm or European corn borer,” said Morton. “As the biocontrol agent continues to break down, it also produces a toxin which will eventually kill the larvae but is safe for humans, animals and other insects. Given how targeted these agents are, much research is being done in this area because of its potential to reduce casualties in other beneficial insects.”
However, Morton does have a caution for growers.
“When using a biopesticide such as Bt or Pseudomonas, it’s important to remember these agents are registered with the Pest Management Regulatory Agency with Health Canada,” he said. “Due care and attention should be paid to all labels for information on application and pre-harvest interval to ensure you can sell your product when you want and for the price you deserve.”