A Pea Weevil outbreak has been recently identified the Wairarapa region. The seed industry is of the view that it the outbreak is confined to this region it may be possible to eradicate it. However if identified in other regions such as the South Island then a different approach will be required. Therefore it is of critical importance to know how wide spread the pea weevil is located. Given that there are no pea crops in the ground during the winter to sample, the only locations where surveillance can take place and where pea weevil can be readily detected is in stored peas.
Given that some seed stores will have large numbers of pea lines it may not be possible to check and sample every line. Therefore it is recommended that if there are more than around 20 lines in store, that a random selection are checked. Crops harvested in 2016, particularly those planted from North Island sourced seed, will be much higher risk, including bypass crops. If have already cleaned some 2016 crops, also check the offal if possible. If unsure about what lines to sample, consult with the seed companies that own the crops in your store.
When inspecting for pea weevil in stored seed there are two actions to undertake.
- Inspect the seed lot and its environs
Please inspect the seed lot and its storage containers carefully for adult weevil. Deliberate movement or disturbance may cause the weevils to emerge out of the seed they have occupied since the last growing season. The adult may also be found in crevices or protected areas in or around the storage container. Close inspection of the pea seeds may expose the larvae or hidden adults that have yet to emerge. They should be easy to spot as the larvae eats out the pea seed as it grows, leaving a large hole like a tooth cavity.
- Test the seed for pea weevil presence.
A good method of detection is to complete a soak test. This procedure should detect with 95% confidence if 1 pea in 1000 is infested. (0.1% infestation level).
Sample methodology is critical to an effective test. Pea weevil do not attack a pea crop evenly but spread in from the boundaries. Therefore parts of the crop will be heavily infested while other parts may have none. A distribution of samples totalling at least 2kg, collected from across the whole seed line is critical in successfully identifying an infestation. In bulk bin or bagged seed lots, a sampling methodology similar to withdrawing an official test sample should be employed. For example, where there are 10 containers or less, every container should be sampled and if more than 50 containers, a minimum of 20 should be sampled.
Silo sampling is more difficult. Take samples from as many points in the silo as possible, as long as it is safe to do so. If a running sample was collected as the silo was filled, use this as source of the seed sample for the weevil check.
- Mix the sample thoroughly then draw about 700g for a soak test. Include any addition suspect looking seed that you have gathered during sampling.
- Place about equal amounts of about 250g in 3 buckets or high sided trays. Smaller amounts are easier to manage.
- Label the tray with the lot identification
- Put in approximately three times the volume of water to peas.
- Soak overnight.
- Inspect the next day looking for stings or shading in the pea or partly emerged adults
- Record the results.
- If pea weevil is found or suspected then place in a specimen jar and despatch to:
David Voice, c/o Ministry for Primary Industries, 14 Sir William Pickering Drive.
Send images to: firstname.lastname@example.org, or ring 0800 80 99 66 and report to MPI.
- Quarantine the line and infested sample and wait for further instructions from MPI.
If you still have concerns about the sampling process or the methodology please consult with any of the major seed companies – PGG Wrightson Seeds, Canterbury Seeds, Midlands, Smith Seeds, Townsend Seeds etc.. or approach the NZ Grain and Seed Trade (NZGSTA) office, ph 03 349 8430