Interfarm UK recommends a double-barrelled Dithane for early and late blight

Nearly half the potatoes planted last year in UK were either highly susceptible or susceptible to Alternaria or early blight and with 100% of all varieties practically susceptible to late blight in the field. Consequently there is an increasing need for a double-barrelled dual-acting fungicide that will prevent both blights.  “That is why growers are turning more and more to Dithane (mancozeb) as it has full label recommendations for the control of both early and late blight and is much more cost-effective than newer alternatives,” says Stewart Woodhead, Technical Manager for Interfarm.

He points out that Markies, Vivaldi, Melody and King Edward are classified as being very susceptible, with other important varieties including Maris Piper, Lady Rosetta, Estima, Melody, Hermes, Fontane, Saxon, Ramos and Saturna being moderately susceptible. “This means that last year 45% of potatoes in the ground could be classified as being susceptible to early blight and so potentially at risk. Virtually all potato varieties grown will get late blight. So it makes absolute sense for growers to protect their potato crops against both blight diseases, by using a fungicide with proven dual activity, such as Dithane,” says Stewart.

“Already a widespread disease in potatoes in Europe, Alternaria is much more of a problem in the UK now, possibly as a direct result of less mancozeb being used in the programme in recent years. But in the UK Alternaria doesn’t appear alone; it is always found with late blight (Phytophthora). So you really need a fungicide with activity on both diseases or you may find yourself having to go in more times to spray, adding to the cost and complexity of the programme.” advises Stewart Woodhead.

He explains that the protectant fungicide mancozeb, as in Dithane NT and Dithane 945, is regarded as a key active against Alternaria in Europe.  “Dithane is one of the few fungicides to have full label recommendations for both diseases. In the UK there are only a handful of products with either label or EAMU approvals for Alternaria. Applying an Alternaria-alone active adds significantly to the cost and the newer dual acting options are much more expensive.”

The rate of use for either Dithane product against late and early potato blight is 2 kg/ha, delivering what experts agree is an effective dose for Alternaria activity, (in excess of 1500 gms.ai./ha). The spray interval is 7 days and the harvest interval is 7 days. The maximum number of applications is 8 per crop, which gives plenty of opportunity to use Dithane throughout the programme.

“It hardly seems possible that mancozeb is now over 50 years old, yet it is still playing such a vital role in the battle against potato blight right across the world. Over these decades we have seen a huge change in the population and severity of potato blight yet mancozeb still controls all known strains of late blight. It retains its position as the multi-site fungicide and is regarded as the foundation fungicide when it comes to managing resistance. With the competitive cost of Dithane, it could be mixed with other fungicides and introduce a multi-site element to the programme, too.”

“Of course Dithane has developed over the years, not least of which in its formulation technology. Compared to the original product, Dithane now has a completely different more advanced formulation which redistributes the active on the leaf surface and gives it excellent rainfastness,” says Stewart.