Many insects have preferred hosts, and some are host specific. If host plants can be manipulated then pest populations can be suppressed or even controlled. Sample pre-season weeds to determine potential pest pressure for crops. Be aware that the introduction of other crops into the area may increase host availability (summer host plants e.g. lucerne and sorghum increase feed availability and survival of Helicoverpa, aphids, and Rutherglen bugs)
Destroy host plants and remove green bridges
‘Green bridge’ refers to the role that weeds and volunteers crops play in helping pests cross from one cropping season into the next. Late summer or early autumn rainfall can trigger the establishment of green bridges in areas where winter cropping dominates. Resulting weeds provide pests with a food source that allows them to develop and increase. They can also increase the risk of disease (particularly viral if the host supports both the virus and the vector). For example, volunteer cereals (if not controlled) can carry barley yellow dwarf virus (BYDV) or wheat streak mosaic virus (WSMV). A green bridge will allow vectors of these viruses (aphids and wheat curl mites) to increase and transmit the virus to the new crops.
Ideally, eradicating green bridges should be an area wide effort. If control occurs only on individual farms, insects can move into crops from neighbouring properties
- Removing volunteer and weed hosts at least two weeks before crops are sown will starve-out many pests
- Target weeds in and adjacent to cropping areas as well as along fence lines and roadsides
- Do not allow weeds to set seed.
Examples of pests that depend on green bridges include:
- Lucerne flea and Bryobia mites – hatched from summer diapause
- Snails and slugs which emerge from summer resting phase
- Aphids and Rutherglen bugs rely on host plants to over-summer (survive)