THE MILD winter has meant that it has been 'open season' for arable crop disease and new evidence suggest that light leaf spot is going to be a particular scourge for oilseed rape growers.

A survey undertaken in December by Bayer’s SpotCheck initiative, showed that 62% of samples assessed contained LLS symptoms three days after incubation.

Mild temperatures throughout the end of 2019 and no prolonged cold spell have resulted in an ideal environment for light leaf spot to develop, particularly latently within the crop. This, coupled with more and more rainfall increasing the likelihood of new infections, has driven up the incidence of LLS in samples assessed by SpotCheck.

Philip Walker, an arable plant pathologist with ADAS, said that the high number of samples identified confirmed suspicions there is a lot of latent disease building in the crop. Looking ahead to the coming months, he warned farmers to be particularly careful if weather conditions continue to stay mild.

“If there is a significant drop in temperatures, we are unlikely to see new infections and any pre-existing infections will pause in development. However, if conditions remain mild then there will likely be more and more infection events in previously symptomless fields," he said.

“A crop carrying high levels of light leaf spot infection into stem extension will be negatively impacted at this vital yield building stage of development. However, the challenge is finding an opportunity to travel on land, given the amount of rain we’ve had.”

This was an observation shared by Grant Reid, Bayer's commercial technical manager for Northern Scotland. He said that while oilseed rape crops looked very small and were struggling towards the end of the year, over Christmas mild conditions have allowed the crop to continue growing away.

“There is a lot of variation in oilseed rape crops – some are what I’d term ‘normal’ for this time of year, while others are struggling. Ground conditions have not been ideal for travelling and I suspect there are a lot of crops out there which have not received a fungicide spray yet.

“Having said that, it is important to remember that oilseed rape is a resilient crop, which branches quite a lot. If you have a crop of around 15 plants/m2, don’t write it off and be patient.

"It is a long time until spring, so continue assessing ground conditions and utilising SpotCheck to understand disease levels in the crop, and when you can, apply a fungicide such as Proline (prothioconazole)," he added.

“Given the difficulties with drilling winter crops, particularly wheat, this season, it may mean that oilseed rape is one of the only paying crops this season,” concludes Mr Reid. “So it is important to utilise all the tools in the armoury, including SpotCheck, to put the crop in the best possible position as it enters stem extension.”