Rapid studies of a pest infestation of salad onions and leeks have confirmed that one of the few treatments available to UK growers to protect their crops no longer works effectively.

  • 12
  • FEB
  • 2018

Onion growers have seen their worst fears realised with confirmation of news that a new population of thrips, one of the industry’s most destructive insect pests and a virus carrier, has survived dosing with spinosad, the main active ingredient of a popular pesticide that was still thought to be effective.

Tests on a sample of the suspect pest delivered to Rothamsted Research late last year were screened by entomologist Steve Foster on behalf of the Agricultural and Horticultural Development Board, which has now confirmed his results. The sample came from crops in southern England.

“We screened this sample collected from the affected crop at various doses in a 72-hour bioassay, and discovered that some of the thrips carried strong resistance to spinosad at the rate applied in the field,” says Foster. Thrips can infest both onions and leeks, which are often grown together.

Onion thrips Credit: Chris Wallwork/AgriiOnion thrips, a destructive pest of onions and leeks, are now more difficult to control                           Credit: Chris Wallwork/Agrii

Foster adds: “I also tested the sample with a pyrethroid insecticide, which was ineffective, with the sample displaying resistance seen in the past in the UK.” He experienced similar problems last year with diamond-back moths on swedes.

While spinosad-resistant populations may not be widespread in the UK, AHDB advises that growers should review their integrated pest management strategies to reduce the risk of further resistance developing.

“Steve is providing information that is critical for the development of effective IPM programmes,” says Dawn Teverson, AHDB Knowledge Exchange Manager. “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.”

Foster’s research at Rothamsted “highlights how important it is to maintain the capability to monitor pests for insecticide resistance in the UK,” says Rosemary Collier, Director of Warwick Crop Centre, part of the University of Warwick.

AHDB is currently reviewing the commissioning of trials to find new controls for thrips on leek and other crops in the wake of the new information on insecticide resistance, using its SPECTREplus crop protection programme, which aims to deliver applied research solutions on high priority disease, pest and weed problems.

Foster’s work at Rothamsted is collaboratively funded by agrochem companies, commodity boards including AHDB, and agronomy companies.

About Rothamsted Research
Rothamsted Research is the longest-running agricultural research institute in the world. We work from gene to field with a proud history of ground-breaking discoveries, from crop treatment to crop protection, from statistical interpretation to soils management. Our founders, in 1843, were the pioneers of modern agriculture, and we are known for our imaginative science and our collaborative influence on fresh thinking and farming practices.
Through independent science and innovation, we make significant contributions to improving agri-food systems in the UK and internationally. In terms of the institute’s economic contribution, the cumulative impact of our work in the UK was calculated to exceed £3000 million a year in 20151. Our strength lies in our systems approach, which combines science and strategic research, interdisciplinary teams and partnerships.
Rothamsted is also home to three unique resources. These National Capabilities are open to researchers from all over the world: The Long-Term Experiments, Rothamsted Insect Survey and the North Wyke Farm Platform.
We are strategically funded by the Biotechnology and Biological Sciences Research Council (BBSRC), with additional support from other national and international funding streams, and from industry. We are also supported by the Lawes Agricultural Trust (LAT).
For more information, visit; Twitter @Rothamsted
1Rothamsted Research and the Value of Excellence: A synthesis of the available evidence, by Séan Rickard (Oct 2015)

The Biotechnology and Biological Sciences Research Council is part of UK Research and Innovation, a non-departmental public body funded by a grant-in-aid from the UK government.
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About LAT
The Lawes Agricultural Trust, established in 1889 by Sir John Bennet Lawes, supports Rothamsted Research’s national and international agricultural science through the provision of land, facilities and funding. LAT, a charitable trust, owns the estates at Harpenden and Broom's Barn, including many of the buildings used by Rothamsted Research. LAT provides an annual research grant to the Director, accommodation for nearly 200 people, and support for fellowships for young scientists from developing countries. LAT also makes capital grants to help modernise facilities at Rothamsted, or invests in new buildings.