26/03/14: Light leaf spot risk remains high

Risk of light leaf spot is high according to an updated forecast from Rothamsted Research. The latest forecast takes into account winter rainfall from December 2013 – February 2014 and shows that risk remains high in all regions and has increased in the south due to heavy rain over winter.

“Growers may need to be particularly vigilant this spring,” explained Dr Neal Evans of Weather INovations (WIN) who put together the forecast. “I suspect the model is underestimating the amount of disease we are seeing. Light leaf spot incidence on pods at harvest last year was low, although stem incidence at the time was moderate to high.”

Pod incidence is one of the key inputs for the forecast as a measure of disease carry over from one season to another.  For future years, it may be possible to combine stem and pod incidence, to tweak the model. This and other aspects of light leaf spot are being looked into be Dr Evans and his colleagues as part of HGCA project RD-2013-3814(Investigating components of the oilseed rape light leaf spot epidemic responsible for increased yield loss to the UK arable industry).

In addition to WIN and HGCA, the project involves scientists from SRUC, ADAS, Rothamsted Research and technical input from Bayer CropScience. Commenting on light leaf spot levels in the field this season, ADAS’s Dr Faye Ritchie said:

“We saw the first signs of the disease at a low level at the end of January.  In some fields the disease remains at a low level but in other, perhaps less sheltered fields, the rain has certainly driven the epidemic along and we see patches of diseased plants where rain-splash has spread the disease from initial foci”.

Dr Jon West, Rothamsted Research added "We were quite surprised when we assessed our experimental field plots this past week.  Some varieties had very little infection whilst others had severe infections and it’s the severity of the infection that has an impact on yield loss.  Overall the level seems moderately high this season but there’s definitely a large varietal effect”.

Further details on varietal resistance to light leaf spot are available in the HGCA Recommended List. To view the forecast, go to http://www.rothamsted.ac.uk/light-leaf-spot-forecast.