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Oilseed rape growers are urged to inspect their crops for phoma disease, especially during the critical three-week period in early October. The AHDB predicts that the peak onset of phoma leaf spot will occur around mid-October this year, with a significant number of sites reaching the 10% symptom threshold by the week starting on October 13th.

Phoma can lead to various issues, from leaf spots to stem cankers, making timely fungicide treatment essential for controlling its spread and reducing yield losses. The AHDB provides an online tool that uses weather data to forecast phoma leaf spot development in oilseed rape plants across hundreds of sites in Great Britain.

For crops showing 10-20% symptoms, it is recommended to treat varieties with lower resistance ratings for stem canker and prioritize smaller crops. Most oilseed rape varieties have moderate resistance levels to phoma stem canker, with some hybrids like Murray and Vegas offering high levels of resistance.

Fungicides have proven effective in controlling phoma leaf spot and stem canker, with two well-timed sprays at half the recommended rate providing good results. It is suggested to consider a second application when reinfection becomes evident, typically 4 to 10 weeks after the first spray.

Various fungicide modes of action, including azoles and non-azole options, can be used for phoma control. To manage resistance effectively, AHDB recommends alternating or mixing different modes of action throughout the fungicide program.

To access phoma forecast information and management guidelines, visit the AHDB website. Integrated pest management is crucial for successful disease management, with proper timing of fungicide treatments being particularly important.

Phoma leaf spot and stem canker in oilseed rape are caused by fungal species that can lead to significant yield losses. Despite the use of costly fungicides, phoma still results in substantial annual yield losses in the UK.

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