Weed Biocontrol

Biological control (biocontrol) involves the introduction of natural enemies (insects, mites and pathogens) of a target weed that will over time reduce the density of the weed to a level that is acceptable (usually below and economic or environmental threshold) maintaining the density at that level. It is an economical, self-sustaining and environmentally friendly management technique. Biocontrol does not eradicate weeds but rather can be used in an integrated approach with a combination of other methods.

Two main biocontrol techniques are used:

1. Classical biocontrol: This is the most commonly used technique and involves the introduction of natural enemies from their native range into an exotic range where their host plant has become a weed. This approach creates a natural, self-sustaining balance between the weed and its control agent, similar to that found in the weed's native range.
2. Non-classical biocontrol: This includes releasing large numbers (inundative releases) of the agent to control the weed, e.g. mycoherbicides and mass rearing and release of large numbers of an insect biocontrol agent.

When a biocontrol agent’s population establishes, control generally becomes self-perpetuating and self-regulating as the agent becomes part of the region's ecology. Monitoring an agent's population dynamics and impact is an important part of a successful biocontrol strategy.

If successfully introduced, biocontrol agents can assist in reducing weed abundance, density and impact. However, successful programs may take 10 or more years to be effective, and results may vary from area to area.

Biocontrol is practical and effective for;

• grazing areas,
• inaccessible areas such as timbered, rocky and steep locations,
• areas of low priority for other forms of control,
• situations where biocontrol is the only option, for example sensitive aquatic or environmental areas,
• situations where chemical control may be too expensive or not effective.

NSW DPIRD staff are involved in the biocontrol of many environmental and agricultural weeds and operate an insect biocontrol quarantine facility at the Orange Agricultural Institute and rearing facilities at the Grafton Primary Industries Institute and Lightning Ridge. NSW DPIRD are currently developing and expanding biocontrol research throughout NSW and have helped develop the National Weed Biocontrol Pipeline Strategy.