A population of onion thrips, collected in the south of England, has been found to contain thrips resistant to spinosad, one of the few effective treatments currently available to growers.
Steve Foster, Rothamsted Research, screened a thrips sample collected from salad onions following reports that Tracer did not appear to be as effective as usual. His tests confirmed that individuals in the population collected had developed resistance to spinosad, the main active in Tracer, when it was applied at the field rate in his bioassays.
Thrips are a group of insects which are prone to insecticide resistance and resistance to pyrethroid insecticides in English populations was confirmed by Steve Foster’s research some years ago.
While the spinosad-resistant populations might not yet be widespread in the UK, growers should review their integrated pest management strategies to reduce the risk of further resistance development.
Dawn Teverson, Knowledge Exchange Manager, AHDB said: “It’s really important that growers know whether a product is going to be effective against the target pest; there seem to be more and more pests showing insecticide resistance. Steve is providing information that is critical for the development of effective IPM programmes.”
Rosemary Collier, Director, Warwick Crop Centre said: “This research highlights how important it is to maintain the capability to monitor pests for insecticide resistance in the UK.”
The AHDB SCEPTREplus crop protection programme is currently reviewing the commissioning of trials to find new controls for this pest on leek and other crops in light of the new information on insecticide resistance.
Onion thrips damage to leek crops from SCEPTREplus control trials