Pest suppressive landscapes
Heavy reliance on pesticides has several downsides, including the risk of insecticide resistance and destruction of beneficial insect populations. There is usually a delay between the arrival of a pest in a cropping paddock and the arrival of the predatory insects (beneficials). In some cases this time delay can force the use of pesticides, which also may affect the beneficials.
A pest suppressive landscape is one where the beneficial insects can find refuge in suitable habitat areas in close proximity to the cropping area. When the pests move into a newly established crop the beneficials can be close behind, potentially providing adequate control of the pest and reducing the need for pesticide application.
Preliminary conclusions from recent research suggest:
- Grain crops near remnant vegetation contain more beneficial insects than those more remote from native vegetation.
- Native plants are rarely ever found to harbour insect pests of crops.
- Native vegetation is a source of beneficial insects such as spiders, lacewings and lady beetles.
- Weeds often harbour pests – this indicates that native landscape with weeds will be less successful.
- Some landscapes appear less prone to invertebrate infestations.
Both pests and beneficial insects (also known as beneficials) can be found in a range of habitats in grain cropping landscapes, throughout the year. Pests are more commonly found on exotic weeds than on native plants and can build up in weedy pastures and crops and on weeds in bushland and other non-crop areas.
Stands of native vegetation offer both opportunities and risks for pest management. Native vegetation remnants in good condition (containing few weeds and with an intact understory) may reduce the number of pests and support beneficials, but can also harbour some crop pests.
Generally, native vegetation remnants in the landscape mean that crop paddocks are in a better position to suppress pests throughout the season.
Distance of remnant native vegetation from the crop appears in some cases to influence the time it takes for beneficial insects to colonise the crop following the arrival of pest species.
Research undertaken in Queensland showed the greater the distance from native remnant vegetation to the crop, the greater the offset in time of colonisation.
While there was a significant offset at the Queensland field site, the same effect was not observed on other field sites in New South Wales, so more data is needed to determine if distance is a consistent factor in pest/beneficials arrival time in crop.
Read more about native species that harbour beneficial insects…