Despite the patchy Phoma forecast growers are being warned against complacency when it comes to OSR disease control this season. That’s the warning from Bayer CropScience’s Tim Nicholson.
 
He points to the variability in the forecast in that at some sites the threshold has already been reached yet other sites in the same county it is predicted considerably later. “The Phoma threshold at Petham, Kent was reached on 22nd September, yet twenty miles away at Manston it is predicted for October 30th. It is a similar picture elsewhere. At Cowlinge in Suffolk the threshold was reached on September 29th, for Wattisham thresholds are expected to be reached on October 29th, a whole month later. Given the highly localised nature of September’s rainfall I would advise growers monitor individual crops to assess disease development, and ensure application timeliness. ”
 
However, his main concern is not where Phoma thresholds are likely to be reached soon but for later in the season where single sprays might be preferred. “For many, autumn disease control strategies have been built on Phoma. Growers know how to spot it, manage it and are fortunate that a range of actives provide protection.”
 
“But it is not the same with Light Leaf Spot (LLS). Identification can be difficult and there are only two actives that offer the most effective protection – prothioconazole and tebuconazole. We’ve seen LLS decimate some crops in the south in recent seasons, which has been due in part to an overriding focus on Phoma. For growers aiming to control Phoma with a single late October or November application they must factor in LLS too,” he warns.
 
And he also urges caution when it comes to rates. “Autumn applications may have to see the crop through until growers can get back in early spring as once the disease is established even prothioconazole and tebuconazole only provide protection against further infection. It simply isn’t a disease with a curative option and I would advise a minimum of 0.46 L/Ha of Proline275 (prothioconazole) at the first sign of autumn infection, with a follow up spray in late winter or early spring for maximum protection,” he concludes.