ANOTHER wet weather disease, phoma in oilseed rape, has meant that this season growers and agronomist should ‘get ahead of the disease’ by preventing yield robbing cankers developing.

The newly-launched Phoma Alert 2017 – an in-field crop monitoring system managed by ADAS, in conjunction with Syngenta – aims to track phoma leaf spot development on varieties with a range of recommended list ratings, to help assess risk and optimise fungicide spray timing. 

Results from last year’s alert systems highlighted the importance of spray application timing and phoma specific fungicide selection – and long before any physical signs of light leaf spot (LLS), reported Syngenta’s technical manager, James Southgate.

Even with the low pressure season in dry conditions last autumn, ADAS crop monitoring for Syngenta’s alert website highlighted that treatment thresholds were typically reached twice before LLS symptoms were seen, particularly on the western and northern sites.

“This season, all the indications are that weather conditions for phoma infection will be reached far earlier,” he advised. “Phoma Alert is invaluable in identifying when disease is likely to strike and indicate when crops need to be regularly inspected for leaf spotting developing.”

ADAS’ plant pathologist, Dr Faye Ritchie, said this year’s wet conditions were favourable to prime spore release from last season’s stem cankers – and some had already occurred at monitoring sites across the country. 

She predicted that the first leaf spot symptoms could start to be seen by the end of this month and into early October.

“For good control, it’s about targeting fungicide applications to thresholds – therefore, first applications when 10 to 20% plants are affected and a follow up application if re-infection is observed later in the autumn.”

Mr Southgate advised that the first application should be Plover, at the first application and that recommendations for any follow up treatment would depend on future weather conditions and the timing for reapplication. There is the option of bolstering LLS activity with a Plover and tebuconazole tank mix if the second application is delayed. 

Although disease resistance is recognised by growers in their variety selection, more recently the emphasis has been on light leaf spot ratings and less on phoma.

“Some 80% of varieties have a phoma stem canker rating of six or below,” added Mr Southgate. 

“But when it comes to leaf spotting in the autumn, Phoma Alert revealed little or no difference between crops with stem canker ratings of four or six. The advice in the field is to treat them all the same when thresholds are reached.” 

He said: “Warmer conditions at the time of infection will lead to quicker movement of infection down the leaf petiole and into the stem – the smaller the leaf at the time of initial spotting, the greater the risk of spread. 

“Growers should be monitoring crops and treating with Plover as soon as the phoma leaf spot threshold is reached. 

Early infection in autumn typically leads to bigger and more damaging stem cankers in the spring, with greater yield losses,” pointed out Mr Southgate.

The Phoma Alert system can be tracked on the Syngenta website: or follow it on Twitter: @syngentacropsuk