Pea weevil: monitoring and control

Pea weevil can cause major damage to field pea crops in spring.

Where have then been reported?

While pea weevil (Bruchus pisorum) is typically more problematic in South Australia than in Victoria and NSW, recent observations serve as a timely reminder that this pest is established in all southern Australian pea growing districts. This spring, pea weevil adults have been found above threshold levels in early flowering field pea crops around Elmore in Victoria’s Northern Country (2 – 6 adult weevils per 10 sweeps). They have also been of concern in recent years around Balliang and Bacchus Marsh in Central Victoria, with agronomists expecting some pea weevil activity this season in these localities. 

About pea weevil

Pea weevil has one generation per year. Adults emerge from hibernation in early spring and fly to the edge of the nearest pea crop when temperatures reach about 20°C. Females lay eggs that are 1.5 mm long, yellow and cigar shaped, on young green pea pods. The larvae hatch 2-4 weeks after egg lay and bore directly into pea pods, where they feed on and in the seeds, before later pupating inside the seeds. Larvae feed for 40-50 days and when fully grown prepare for emergence by chewing a circular 3 mm hole in the seeds before pupation takes place. Pupation takes approximately 2 weeks, and the new generation of adult beetles emerge over several months to hibernate in sheltered areas such as silos and sheds until the following spring.

Pea weevil eggs (top) and larvae (bottom) (Source: SARDI)

 

Pea weevils invade pea crops irrespective of whether the crop is flowering. They usually invade for 3-4 weeks and lay eggs for a similar time. After initially settling in edges, beetles disperse into the crop by a series of short flights. As larvae bore immediately into pods after hatching, they are almost never exposed to insecticide sprays. Pea weevils cannot reproduce in stored grain and infestations can only occur if eggs are laid into green pea pods in growing crops.

Pea weevil is not a true weevil and does not have the typical weevil snout. Adult pea weevils are chunky beetles (5 mm long), and are most often brownish and flecked with white, black and grey patches. The legless larvae are curled, cream in colour, and reach a length of about 5 mm.

Pea weevil adult (Source: cesar)

 

Our advice

Monitoring in spring to determine the necessity to spray, and spray timing are two key components of an effective strategy to prevent widespread crop damage, and to avoid downgrading or rejection of grain at receival sites. 

Monitoring pea crops for the presence of pea weevil is best done using a sweep net on calm days. Start monitoring when flowering first begins, and continue through to when the crop begins to dry. Sweep along the crop edge at least 2 m into the crop, starting adjacent to any nearby hibernation sites such as tree-lines, sheds, etc. Sweep in a 180° arc while walking forward. After every 25 sweeps, count the number of weevils, and repeat at 5-10 sites around the crop edge.

Spraying is recommended if there is an average of 2 or more weevils per 25 sweeps. Pea weevil adults must be controlled before they lay eggs on the pea pods.

For a comprehensive guide on pea weevil control including cultural and post-harvest controls, see the SARDI Pea Weevil Factsheet.

 

Acknowledgements

This PestFacts article has been adapted from the pea weevil PestNote developed by Bill Kimber (SARDI).

 

Field reports

Chris Dunn – Landmark (North Central, VIC)

Alistair Tippet – Landmark (Central, VIC)