Products containing metalaxyl-M have again been found to be ineffective at controlling downy mildew in column stocks, latest AHDB-funded research shows.
The fungicide sensitivity trial reinforced the importance of rotating plant protection products with different modes of action.
The research was conducted after UK and Dutch column stocks growers experienced serious problems controlling downy mildew (Peronospora parasitica) on crops during the 2018 season, leading to substantial losses.
Independent trials to test fungicide performance were undertaken by the James Hutton Institute (JHI) in Scotland this year, as part of a £294,000 AHDB-funded project to tackle downy mildew and late blight.
The results generated were similar to those from trials managed by the AHDB Cut Flower Centre in 2018 to test fungicide performance, which also showed that products containing metalaxyl-M were ineffective at controlling downy mildew.
Recommendations from those trials were implemented successfully by industry in 2019, minimising crop losses.
Wayne Brough, AHDB Knowledge Exchange Manager, said: “To gain the best level of disease control, a range of cultural and nursery hygiene measures need to be used along with a more intensive spray programme”.
“The results from JHI reconfirm what we found in earlier trials managed by the Cut Flower Centre and our suggested spray programme can be used in the 2020 growing season without significant changes.”
Cathryn Lambourne, AHDB Crop Protection Senior Scientist, said: “Our new downy mildew programme is developing methods to detect disease in seeds, tests to understand fungicide resistance and tools for real-time disease risk monitoring, as well as gathering and developing information on improved cultural control options.
“These early results from JHI stress the importance of managing resistance build-up and ensuring that plant protection products with different modes of action are used in a spray programme.”
A range of disease isolates were tested against a number of fungicides, including: dimethomorph (Paarat), fosetyl-aluminium and propamocarb hydrochloride (Previcur Energy) mandipropamid (Revus) and metalaxyl-M.
The sensitivity to approved fungicides will continue to be monitored in future trials.
Growers and agronomists can find the full results of the 2018 trials, including an example spray programme, in the factsheet: ‘Maintaining successful control of downy mildew in protected crops of cut flower column stocks’