Results show control holding for now, but mixture is safest move

  • 09
  • AUG
  • 2021

The fungus responsible for light leaf spot, the UK’s most important oilseed rape disease, is becoming increasingly resistant to azole fungicides but not QoI or SDHI fungicides.

However, despite the differences identified in laboratory testing, both azole and non-azole products are still performing similarly when applied to control light leaf spot in the field.

The lead author of a new study into its resistance status says the results support the use of a mixture of an azole plus a Qoi/SDHI for robust disease control.

Rothamsted’s Dr Kevin King said: “Azoles are still effective, but they are becoming less so and continued sensitivity monitoring is needed to ensure optimal strategies are being deployed.”

Traditionally a bigger problem in the north of the UK, light leaf spot has now become the UK’s most important disease of brassicas and can potentially reduce yields considerably if left untreated.

Light leaf spot is also major headache for brassica growers across Europe, Australia and New Zealand, and most recently the US Pacific northwest, where the disease is instead termed chlorotic leaf spot.

Published in the journal Plant Pathology, the study looked at populations throughout Europe of the fungus responsible for light leaf spot, Pyrenopeziza brassicae.

It showed increasingly complex variants of the gene targeted by azole fungicides are now widespread, and in lab testing these are far less sensitive to azole fungicides.

Regional differences were also identified within the UK, with northern populations less sensitive than southern ones.

There were also differences between different European populations – for example Danish populations were much more sensitive to azoles than either UK or German populations.

The news is better for growers in the US, with the P. brassicae population there still highly sensitive to azole, QoI and SDHI fungicides.

According to Dr King, the P. brassicae fungus shows especially high genetic diversity, which means it has a considerable ability to evolve fungicide resistance.

“However, fungicides represent only part of a disease management strategy. Integrated approaches such as the use of crop varieties with good resistance to disease, will offer flexibility with fungicide timings as well as improved disease control. Similarly, there is a need to use a range of fungicides that work in different ways, to slow the selection for resistance.”

This work was a collaborative study between Rothamsted, ADAS, and NIAB in the UK; TEAGASC in Ireland; IHAR-PIB in Poland; and Nanjing Agricultural University in China.

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.
BBSRC invests in world-class bioscience research and training on behalf of the UK public. Our aim is to further scientific knowledge, to promote economic growth, wealth and job creation and to improve quality of life in the UK and beyond.
Funded by government, BBSRC invested £469 million in world-class bioscience in 2016-17. We support research and training in universities and strategically funded institutes. BBSRC research and the people we fund are helping society to meet major challenges, including food security, green energy and healthier, longer lives. Our investments underpin important UK economic sectors, such as farming, food, industrial biotechnology and pharmaceuticals.
More information about BBSRC, our science and our impact.
More information about BBSRC strategically funded institutes

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.