Despite the patchy Phoma forecast growers are beingwarned against complacency when it comes to OSR disease control this season.Thats the warning from Bayer CropSciences Tim Nicholson.
He points to thevariability in the forecast in that at some sites the threshold has alreadybeen reached yet other sites in the same county it is predicted considerablylater. The phoma threshold atPetham, Kent was reached on 22nd September, yet twenty miles away atManston it is predicted for October 30th. It is a similar pictureelsewhere. 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 Septembers rainfallI would advise growers monitor individual crops to assess disease development,and ensure application timeliness.
However, his mainconcern is not where phomathresholds are likely to be reached soon but for later in the season wheresingle sprays might be preferred. For many, autumn disease control strategieshave been built on Phoma.Growers know how to spot it, manage it and are fortunate that a range ofactives provide protection.
But it is not thesame with light leaf spot (LLS). Identification can be difficult and there areonly two actives that offer the most effective protection prothioconazole andtebuconazole. Weve seen LLS decimate some crops in the south in recentseasons, which has been due in part to an overriding focus on Phoma. For growers aiming to control Phoma with a single late October orNovember application they must factor in LLS too, he warns.
And he also urgescaution when it comes to rates. Autumn applications may have to see the cropthrough until growers can get back in early spring as once the disease isestablished even prothioconazole and tebuconazole only provide protectionagainst further infection. It simply isnt a disease with a curative option andI would advise a minimum of 0.46 L/Ha of Proline275(prothioconazole) at the first sign of autumn infection, with a follow up sprayin late winter or early spring for maximum protection, he concludes.