Bean crop being sprayed© Tim Scrivener

In 2015, testing carried out by Rothamsted Research and the PGRO confirmed pyrethroid resistance in the pea and bean weevil.

PGRO technical officer Becky Ward says the work confirmed strong or partial resistance to pyrethroids on a number of sites in the east of England (see map below).

Pulse growers have had to rely on pyrethroids as the only chemical means of controlling weevils since the early 1990s, when systemic organophosphate insecticides were banned.

That reliance has resulted in resistance and Ms Ward says the PGRO is working with agrochemical companies to look at approvals for alternative products.

“For the time being, in areas where there isn’t resistance we still have to rely on pyrethroids, as there is no new chemistry available,” she says.

See also: Pea and bean weevil found resistant to insecticide

Subsequently, the PGRO is working with Rothamsted researchers to seek alternatives and Ms Ward says the prototype “lure-and-kill” system has “a promising outlook”.

Pea and bean weevil map

Pheromones are used to lure weevils into devices laced with a fungal disease that kills the pest. The fungus sticks to the weevils, which return to the crop and spread the pathogen to other weevils.

The system is in its first year of trials and will also be tested on the bruchid beetle – another pest suspected to be resistant to pyrethroids.

She says the concept is yet to be proven, but as the fungal pathogen is classed as a biocontrol agent, it has to go through the same approvals process as other pesticides.

“We have been reliant on chemicals, so we need these tools to provide solutions for growers, but it will take time to get it through the approvals process.

“The other possibility is that the devices could be placed in crops in the autumn to trap the second generation [of adult weevils] before the spring season starts,” says Ms Ward.

In the meantime, she urges growers to use pheromone traps on previous pea and bean field margins in mid-February to monitor weevil activity.

The traps can indicate numbers, peak migration and the optimum timing for drilling and insecticide sprays. The spray threshold is breached when 30 or more weevils are caught in one recording day.