Syngenta warns potato growers not to compromise blight control programmes during high risk conditions when tackling the threat of Alternaria. “During the current high blight risk periods, growers need to be maintaining the best possible control with Revus-based programmes, and addressing the threat of Alternaria as a separate issue,” advises Glenn Wilkinson of Syngenta Crop Protection UK.
Norfolk agronomist Simon Alexander believes blight products containing mancozeb at less than the current full rate of 1500g ai per hectare have limited effect on Alternaria. He reports one grower used fungicides containing mancozeb in every application on a field of Markies over the Alternaria risk period in 2008, but the crop was still severely hit by the disease. “Using straight mancozeb, to apply sufficient ai for any possible effect on Alternaria, could compromise blight control,” he adds.
This season Syngenta is piloting a new AlternariaCAST forecasting system with a group of growers and agronomists in the eastern counties and Shropshire, where the most severe disease attacks have been recorded. Mr Wilkinson added: “For the optimum Alternaria control treatment should take place before the typical leaf spotting signs of infection are visible. The aim is that AlternariaCAST will give a reliable forecast of conditions conducive to disease, and enable growers to time applications more effectively.”
