With Phoma infections forecast earlier than ever this season, oilseed rape growers and agronomist now have the chance to get ahead of disease attacks and prevent yield robbing cankers developing, with Phoma Alert 2017.
In-field crop monitoring managed by Adas, in conjunction with Syngenta, will 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 Phoma Alert highlighted the importance of spray application timing and Phoma specific fungicide selection, which was long before any signs of Light Leaf Spot (LLS), reported Syngenta technical manager, James Southgate.
Even with the low pressure season in dry conditions last autumn, ADAS crop monitoring for the Syngenta Phoma Alert website highlighted Phoma 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, highlighted the wet conditions favourable to prime spore release from last season’s stem cankers had already occurred at monitoring sites across the country. She predicted first leaf spot symptoms could start to be seen at the end of September.
“Phoma Alert is useful as it will help to identify when phoma is active and provide information on how disease is developing across a range of reference varieties with different resistance ratings”she advised. “For good Phoma 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”. ”
James advised the implication for agronomic decision making was to treat purely for Phoma, using Plover, at the first application. Recommendations for any follow up treatment would depend on future weather conditions and the timing for reapplication – with the option to bolster the LLS activity with a Plover and tebuconazole tank mix if the second application is delayed.
In the driest Eastern counties, James highlighted Phoma Alert indicated for some crops just one treatment would have sufficed last autumn, using the tank-mix option. But in the north and west, when infected crops reached the second treatment threshold in December, there was still no LLS reported.
And in an early first application timing – such as we could see this season – a two-spray strategy has invariably paid dividends in higher yields, he added.
Although disease resistance is recognised by growers as a key attribute of 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,” according to James. “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 advocated growers should assess the risk to crops, based on seedling size; drilling date; weather conditions and the appearance of Phoma spots on the leaf.
“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,” he advised.
“Early infection in the autumn typically leads to bigger and more damaging stem cankers in the spring, with greater yield losses,” he pointed out.
In season Phoma Alert information can be tracked on the Syngenta website: www,syngenta.co.uk and follow on Twitter: @syngentacropsuk