Light leaf spot disease risk high for most GB regions, says forecast

The autumn light leaf spot (LLS) forecast shows that the risk of LLS development in GB winter oilseed rape (WOSR) is high for the third year running.

Hosted by Rothamsted Research and supported by AHDB Cereals & Oilseeds and Bayer CropScience, the regional forecasts show the proportion of crops predicted to have greater than 25 per cent of plants affected by LLS (based on disease incidence at 79 fields in the previous season and weather data).

High levels of disease were generally observed on WOSR stem and pods before harvest and this has resulted in a high inoculum carry-over potential into this season’s crops for most GB regions.

Regional risk results

Regional risk is broadly similar to 2015–16. Some regions are, however, at a higher risk this year (South West and South East of England), whereas some are at a lower risk (South of England).

East Anglia, which is generally warmer and drier than other regions, is, once again, the region forecast to be at the lowest risk of LLS.

Calculate your risk

Dr Neal Evans, plant pathologist at Weather INnovations (WIN), who puts together the forecast, said: “Many factors influence the risk of disease development and we are reminding people to visit the LLS web page to build a customised forecast.

“This allows the influence of variety, sowing date and autumn fungicides to be factored in but it is important to remember that the disease doesn’t adhere to borders and the forecast can only ever provide an indication of risk.

“If you farm on a border where there is a risk ‘clash’, such as East Anglia and the East of England, your risk is likely to be around halfway between the two.

“As always, the best way to know what is going on in a particular field is to take plant samples and put them in polythene bags at 10–15°C for 4–5 days to help bring out symptoms.”

Protecting your crop

Vigilance is key, especially for varieties with LLS resistance ratings below 6, which have not received a phoma spray, so the disease can be detected and sprayed before it become established.

Following any autumn sprays, January and February 2017 will be the next important period for LLS control.

Paul Gosling, who manages fungicide performance work at AHDB, said: “The threshold of 25 per cent of plants affected only applies at the early stem extension stage.

“If LLS is found before this, there is no threshold and early treatment is recommended to prevent the disease spreading within the crop.

“Our fungicide performance trials show several products can achieve similar levels of control.

“Product choice will be ultimately guided by other considerations, such as product activity against phoma leaf spot and plant growth regulatory activity.”