Pea weevil (Bruchus pisorum) in field peas
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||Budding to Pod maturity
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|Pea weevils are now established in all major field pea regions of southern Australia. Although the incidence of pea weevil has declined over the past decade, a failure to manage it well may result in an increase in pea weevil populations.
||Pea weevil infestation is initially restricted to the crop edge where the beetles first land when they move from overwintering sites around the field
- Orange-yellow, cigar shaped eggs on the surface of developing pods.
- Larvae leave the egg and bore directly into developing seeds where they feed until mature
- Can reduce seed weight by up to 25%
- May reduce germination by up to 75%.
- Beetles emerge from seed by chewing a hole in the seed coat. Beetles can emerge from seed in the field, or in storage.
- Damaged seed has a characteristic round exit hole and cavity where the larva has fed and developed.
||It is critical to prevent the laying of the pea weevil eggs on the developing pea pods. Monitor:
- Every 3-4 days from flowering onwards
- Use a sweep net once spring temperatures are sufficiently high for PW adults to leave their overwintering sites and move into crops (>18°C).
- Check crop edges from the start of flowering.
- Take 25 sweeps along a 1-5 m band around crop edges – concentrate on areas adjacent to trees or other structures (overwintering sites).
- Repeat at 5 or more sites around the field – calculate average number of beetles
- Also sample well into the crop (>50 m) if high numbers are found on the edges. Beetles may have moved further if they have been in the crop for some time.
- Only sow seeds free of pea weevil
- Fumigate after harvest if using farmer kept seed
- Control volunteer field peas to minimise pea weevil survival
- Clean up areas of baled pea stubble, or unharvested portions of field pea paddocks to minimise sources for next season’s infestation
- Harvest early to prevent yield loss, minimise emergence, and reduce hibernating populations
- Graze fields to reduce spilt seed and to reduce pea weevil numbers hibernating
- Field peas for hay production should be cut at flowering (before pod development)
- Fumigate in sealed silos – kill larvae to reduce seed weight loss and live insects at delivery.
- Segregate seed from crop edges from the rest of the crop during harvest to reduce the proportion of infested grain.
- Seed for sowing the following year should only be kept from the centre of the paddock.
- Clean up spilled seed in paddocks and around storage sites
- Dun peas – 2 beetles/25 sweeps
- White peas – 1 beetle/25 sweeps
Border spray if there is average of 2 or more weevils per site.
- It is assumed that pea weevil is present in all pea growing regions
- A border spray (to 50-60m) is the most effective means of control, especially in large paddocks.
- Use sweep net results to determine where spraying is required, especially in irregular shaped paddocks and where trees are present in the middle of paddocks.
- Two or more border sprays or whole crop sprays maybe required where above threshold numbers of pea weevils are found following initial spray application.
- Spray whole crop if pea weevils are in high numbers in small paddocks or if found near the middle of the crop.
- Spray before egg lays commence as insecticides are not effective against eggs.
- Egg lay occurs about 2 weeks after beetle arrival in the crop – take delay in egg lay into account when deciding control measures – beetle flights can occur over several weeks.
- Target insecticide application after first flower and once pea weevil are detected and preferably before most pods develop
- Registered rates of synthetic pyrethroids kill adult pea weevils and are effective (at full label rates) at deterring pea weevils from laying eggs for about 18 days after application.
- Check crops 14 days after the first spray. Consider a second spray if pea weevils are still present.
- Fumigate all purchased seed in gas tight silo for 21 days with phosphine.
- Pea weevils that are not controlled in this season’s crop will multiply to become a bigger problem in future years.
- Synthetic pyrethroids can flare other pests such as helicoverpa and aphids.
- SPs also kill beneficials that may keep other pests in check.
- A border spray will reduce the overall impact of applying a synthetic pyrethroid for PW control.
- Monitor for other pests at the same time as for pea weevils.
- Spray pea weevils at threshold but beware of and monitor for other pests
- Pea weevil control is an area wide management issue. Local populations can be driven to very low, sub threshold levels with a concerted effort to manage them well in all pea crops.
|Communicate and discuss management of pea weevil
||Agronomists and growers can discuss:
- Management of weeds and volunteers
- Monitoring programs
- Seed sources
- Spray management plans and marketing options
Industry publications provide up to date information about regional pest issues