UK primed for mass eruption of phoma spores

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The UK is primed for a mass eruption of phoma leaf spot spores during early to mid-October, according to experts.

This warning was issued alongside the critical October update of the AHDB Cereals & Oilseeds-funded phoma leaf spot forecast.

Hosted by Rothamsted Research, the forecast uses temperature and rainfall data (from the summer to early autumn period) to provide information on potential disease pressure and guide spray decisions against phoma.

With plenty of rain throughout August and unsettled conditions predicted for the foreseeable future, all UK regions are forecast to be at risk from a mass eruption of airborne spores during early to mid-October.

Due to the importance of localised rain/wetting events, the timing of visible leaf spot symptoms is forecast to vary tremendously across the UK.

Compared to last year, some sites are forecast to have earlier onset of symptoms, some similar and some later.

In autumn, fungal spores are released from infected crop stubble.

The spores infect young susceptible leaves which then develop the characteristic leaf spot. Fungi then grow from the leaf into the leaf petiole and then infect the plant stem – the smaller the plant, the quicker this step can occur. Once in the stem, the fungi kill tissue causing visible phoma stem cankers in the late spring and through the summer.