Reference crops in Hertfordshire, Yorkshire and Cambridgeshire will be monitored weekly to enable growers to more accurately time sprayings spray timing assessing the relative value of varietal disease resistance ratings.
Phoma leaf spotting could start to become evident by early October according to ADAS plant pathologist, Faye Ritche.
"We know that many areas have already received the critical 20 days with rainfall from the 1st August, which has primed cankers on last year’s crop trash to release ascospores," Ritchie said.
"With each further rain event, repeated spore releases would be triggered and, with crops infected, the onset of characteristic leaf spotting."
Ritchie warned that, unless leaf spots are controlled, infection will imperceptibly move down the petiole to reach the stem. The earlier that stems are infected, the greater the size of canker that will develop in the spring, and the worse the effect on yield.
"Backward crops are more susceptible, since infection will move to the stem faster on smaller leaves; particularly if weather conditions remain mild when disease development is faster," she advised.
"Varietal resistance appears to help growers by slowing the development of infection on the leaf, which could gain valuable flexibility in fungicide timing.
"The Phoma Alert monitoring will help give practical guidance as to how the resistance ratings could help tailor fungicide programmes," advocated Faye.