Rory MacLellan, MPI
A Government programme to wipe out pea weevil Bruchus pisorum, has achieved a world first, with Biosecurity New Zealand announcing the successful eradication of the noxious pest from Wairarapa.
This means the nearly four-year ban on pea (Pisum sativum L.) plants and straw has been lifted. Commercial and home gardeners can again grow pea plants and use pea straw as garden bedding material. Biosecurity New Zealand has been working with Wairarapa farmers since March 2016 to contain pea weevil that threatened to put a major dent in the country’s $130 million pea industry.
The pea weevil, an unwanted organism under the Biosecurity Act 1993, was confirmed in harvested pea seeds in Wairarapa, New Zealand on 4 April 2016. Bruchus pisorum is strictly monophagous, relying onpea plants to complete its life cycle. Weevils spread by flight and travel in infected pea seed, straw or dirty farm machinery. The larvae feed on young peas and heavy infestations can decrease pea production by 10–15% seriously affecting seed weight, germination and increasing productivity costs. Peas are an important economic crop for New Zealand, annually earning $50 million domestically and $80 million in exports. Therefore, weevil-infested peas could threaten both markets. The Ministry for Primary Industries (MPI) initiated a biosecurity response to the pea weevil incursion to determine: if there was a breeding population; its distribution in the Wairarapa; and if there had been any spread to other pea growing areas of New Zealand. The objective of the response was eradication should a population be present. MPI in partnership with the pea industry, issued a Controlled Area Notice (CAN) in the Wairarapa enforcing a ban on growing peas within a specified area and placed controls on moving pea material within, in and out of that area. Surveillance surveys were undertaken within pea crops in New Zealand grown outside the Wairarapa to determine if the pea weevil had spread outside of the CAN. Within the controlled area, delimiting surveys were undertaken by multiple sweep-net sampling inspections of flowering peas planted in trap-crop pea plots containing early and late varieties (Figure 1).
Figure 1: Pea weevil sweep-net inspection
Insecticides and herbicides were applied to the plots once flowering had finished, killing any weevils that may be present and the pea plants, which were also mulched to ensure desiccation and prevent regrowth (Figure 2).
Two years of negative detections from the pea growing areas outside the controlled area confirmed the absence of pea weevil. Within the controlled area, a decrease of 99.1% of the pea weevil population was recorded from year one to two (2016 and 2017) and zero detections in 2018 and 2019, confirming the eradication of pea weevil from New Zealand.
Figure 2: Pea weevil early-variety traps crops desiccated and mulched, late variety still flowering
The response shows what can be achieved when Government, industry and communities work together. In this case, the destructive insect was detected early and in a region with mountain ranges providing natural borders to restrict natural spread. However, the most important aspect of this response was the awareness and support within the local community in the banning of growing pea plants. This removed the plant required for the pea weevil to complete its life cycle, decreasing the population until it died out and eradication declared.