Pea weevil spray dates
Pea weevil has commenced emergence from winter hibernation and invasion of pea crops. Now is the time to begin monitoring podding pea crops for pea weevil adults. Where adult densities exceed threshold guidelines, border treatment should occur on the optimal spray dates. Optimal timing of insecticide applications is essential for effective pea weevil control during spring. Where required, border treatment should occur after the majority of adults have invaded pea crops, but before they become reproductively mature and lay eggs.
Based on recent and forecast temperatures, the SARDI pea weevil model predicts that crop invasion by adults commenced in mid-August. Following emergence, adults typically take 10-14 days to mature ovaries before egg-lay, dependent on temperature.
We therefore advise that podding pea crops that require border treatment should be sprayed around the first week of September. As temperature forecasts are updated over the next two weeks, we will provide tighter spray dates through PestFacts and Twitter; Follow us on Twitter @PestFactsSARDI to keep updated.
To monitor, use a sweep net at 5-7 day intervals around edge of pea crops, to about two metres into the crop. Pea weevil adults are 5mm long, chunky, brownish beetles flecked with white, black and grey patches. The tip of the abdomen extends beyond the wing covers and is white-marked with two oval black spots. They are not true weevils and adults lack the characteristic weevil snout. Eggs are yellow, cigar-shaped and 1.5 mm in length.
If adult densities exceed at least 1 adult per 10 sweeps, averaged across multiple locations, podding pea crops should be border sprayed to a width of 20-40 metres on the optimal dates using a registered insecticide. For pea crops not yet podding by the first week of September, spraying should occur as required once the first flowers wither and set pods. After pea weevil treatment, monitoring and threshold-based treatment for native budworm, Helicoverpa punctigera, should continue as normal.
Pea weevil, Bruchus pisorum, adults invade crops in late winter / early spring and lay eggs on developing pods. After hatching, larvae enter pods to feed on the developing seeds and remain undetected until around harvest. Adult beetles exit from infested grains via neat round holes, with the first beetles emerging 3-4 weeks after peas are first ready for harvest and emergence continuing in storage. The presence of live adults can result in rejection of grain at delivery. Pea weevil populations can carry over into subsequent seasons within a local area. The adults emerge during summer from local sources of infested seed and disperse into local surroundings, where they hibernate during winter. Sources of local emergence include delayed harvest (allowing some adults to emerge pre-harvest, and/or increased shattering of infested grain), infested grain not fumigated and retained on-site, or inadequate farm hygiene.
Pea weevil can be effectively managed using an area-wide approach, where all growers in a district practice the following:
- Well-timed spring monitoring and spraying to control adults before egg lay; concentrating monitoring near hibernation sites (e.g. pine trees, sheds).
- Harvesting peas as early as possible, as soon as sufficiently dry, to pre-empt the emergence of new adults from grain and avoid shattering. This prevents adults dispersing into local hibernation sites and carrying over into next season.
- Fumigate harvested grain that appears to be infested.
- Good farm hygiene: Avoid unintentionally introducing infested seed from a supplier, clean up grain residues and control volunteer peas.