A phoma leaf spot forecast shows that the south west has already reached the treatment threshold for the disease.

The forecast funded by AHDB uses temperature and rainfall data from the summer to early autumn period to provide information on potential disease pressure.

Visual reports from fields in these areas confirm that treatment thresholds have been reached at sites located in the south west.

Application timing is the key to success for phoma control and the forecasts can be used to focus crop walking and guide spray decisions against phoma.

The UK forecast map uses a colour-coded system to show how long it will take for each site monitored to reach the spray threshold of 10 per cent of plants affected.

Dr Neal Evans of Weather Innovations Consulting LLP (WIN), who put the forecast together, said: “The mild autumn and wet August and September have really pushed the development of the fungus on this year. It’s led to the early release of airborne spores and the appearance of leaf infections at the earliest time for several seasons.”

Recent additions to the AHDB Recommended List (RL) have added strength to the overall resistance to phoma stem canker, with several varieties having a resistance rating of 8.

There are several varieties, however, with relatively low resistance ratings (3 to 4). These should be the priority for treatment, particular for backward crops.

Making a spray application as close as possible to the threshold timing can help maximise the effect of fungicides.

The latest fungicide performance information shows good control can be achieved with half rates applied as a two-spray programme

A second spray should be made when re-infection is evident – typically four to ten weeks after the first spray.

Fungicide performance information and the phoma forecast can be accessed via cereals.ahdb.org.uk/osrdisease