While the blight situation for 2010 remains largely an unknown, Malcolm Smith, Masstock’s technical support manager, describes how best to get equipped against the emerging presence of Alternaria in potato crops. “Alternaria, otherwise known as ‘early blight,’ has been the focus of much attention for this coming season,” comments Malcolm. Well established in the USA, it is a bigger threat than even late blight there – “and although it isn’t common to the UK, it does ‘crop up’ every now and again – it isn’t a ‘new’ disease by any means.” Referring to a number of bad Alternaria attacks observed in UK crops last year, Malcolm says that there is a lot of it around. “Its presence is very easily recognised,” he says. “Leaf symptoms are quite different to that of Phytophthora infestans – the fungus responsible for late blight. But distinguishing which of the two species of Alternaria you have in your crop, be it Alternaria alternata or Alternaria solani, is nigh on impossible in the field. “Markies and Saturna are two varieties which were strongly affected in 2009,” reports Malcolm. “However varietal resistance to Alternaria in the main UK potato varieties isn’t well characterised – so growing specific varieties is unlikely to offer a significant control measure. “The real trigger for last year’s infections was the hot spell we had back in June,” believes Malcolm. “Temperature is the main factor. High temperatures really favour its development – which is likely to be why it’s not normally so much of a problem here in the UK,” he adds. Alternating periods of wet and dry conditions are also favourable to spore germination and the spread of infection. But even with the possible risk from Alternaria, Malcolm reminds growers that anything could happen during these coming months. “Alternaria does pose a consideration for control but growers preparing their programmes really must ensure the focus remains on late blight,” he urges. “I am a keen supporter of the newer chemistry such as Valbon, Revus, Ranman and Electis. Growers should be planning their programme, taking into consideration the various attributes of the products, and ensuring they have a robust strategy incorporating a range of different modes of action,” he recommends. “By no means do we have the whole answer, but the inclusion of mancozeb co-formulations within your armoury can provide additional advantages to Alternaria control as well as providing a robust late blight strategy. “Valbon (benthiavalicarb and mancozeb) is one option that has a fit early on in the programme. Timed best during the full stable canopy stage it provides some much needed kick-back and protectant activity against foliar blight. “Mancozeb is a very useful active with a reasonable level of activity on Alternaria,” notes Malcolm. Its use in co-formulations, such as within Valbon, is useful in giving late blight treatments activity against Alternaria,but is also beneficial for anti-resistance strategies by providing multi-site activity against foliar late blight. Growers are advised to apply no less than the maximum recommended rates, at tightened spray intervals, recommends Malcolm. “With more aggressive and continually evolving blight populations the need for a robust and sustained defence strategy is a must to prevent blight in crops. There really should be no let up.” |