Pea weevil (Bruchus pisorum) 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.
Insects and damage
Image: SARDI
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% and 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.
Adults leave their overwintering sites and move into crops once spring temperatures reach about 18°C
Monitoring
It is critical to prevent the laying of the pea weevil eggs on the developing pea pods. Monitor the crop every 3-4 days from flowering onwards, with emphasis on field edges and areas adjacent to trees or other structures (overwintering sites).
Take 25 sweeps along a 1-5 m band around crop edges. Repeat at 5 or more sites around the field and 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.
Beneficials
None known
Cultural control
Only sow seeds free of pea weevil (fumigate after harvest if using farmer-kept seed).
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.
Control volunteer field peas to minimise pea weevil survival, and clean up areas of baled pea stubble, clean up spilled seed in paddocks and around storage sites 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.
Thresholds
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.
Pesticides
It is assumed that pea weevil is present in all pea growing regions. 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.
A border spray (to 50-60 m) is the most effective means of control, especially in large 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). Egg hatch in 14-28 days.
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.
Multi-pest considerations
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.
Spray pea weevils at threshold but beware of and monitor for other pests
Communication
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.
Industry publications provide up to date information about regional pest issues
