Concern over the increasing threat of early blight, named Alternaria, as well as more aggressive late blight in the UK should lead potato growers to return to Dithane (mancozeb) as their fungicide of choice in potatoes for blight management programmes this year, according to an expert.

Dr David Stormonth, technical manager for Interfarm UK Ltd, believes Alternaria has become much more of a problem in the UK, but it is always alongside late blight and is rarely found in isolation.

Growers will therefore need fungicides with dual activity on both these diseases. The protectant fungicide mancozeb is regarded as a key active against Alternaria on the continent, where this disease is a significant problem, and the newly re-registered Dithane now has a label recommendation for early blight in potatoes in the UK.

Stormonth said: “Curiously there is some view that the decline in the use of mancozeb as the mainstay active in blight programmes could have some impact on the reported increased risk of Alternaria, as most other blight fungicides, particularly the newer chemistry, have little or no activity on this disease.

“It makes no sense to apply a product for Alternaria alone, but does make sense to incorporate Dithane into programmes to keep both early and late blight under control, particularly if growing susceptible varieties such as Markies and Maris Piper. You could consider mixing straight Dithane to other late blight products to increase the mancozeb concentration and assist in keeping Alternaria under control.

“Both fungicides are fully available to UK growers this year, as the manufacture and supply chain issues experienced last year have now been overcome. We anticipate that growers should not have any problems getting either product and so will be in a position to enjoy highly cost-effective, multi-site protection against potato blight.

“Dithane NT and Dithane 945 have both been re-registered onto Annex III by UK’s CRD this year and have new MAPP numbers and refreshed labels, supported by modern, up-to-date field data for crops and diseases listed. Re-registration means that Dithane has had to prove that it is effective against both early and late potato blight and so is a strong independent affirmation of the products’ efficacy.”

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