Dual-purpose Dithane for early and late blight

With late blight becoming more aggressive, new strains developing and the threat of early blight (Alternaria) increasing in potatoes, growers are turning to Dithane (mancozeb) as it has full label recommendations for the control of both early and late blight and is particularly cost-effective.

"Already a widespread disease in potatoes in Europe, Alternaria has become much more of a problem in the UK, possibly as a direct result of less mancozeb being used in the programme in recent years. But in the UK Alternaria rarely appears alone; it is usually found together with late blight (Phytophthora). So you really need a product 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 Dr. David Stormonth, Technical Manager for Interfarm.

He points out that Alternaria is usually associated with particular susceptible potato varieties. “Markies is classified as being very susceptible, with other important varieties including Maris Piper, Estima, Lady Rosetta, Hermes and Saturna being moderately susceptible. In fact the top four varieties grown are all susceptible to Alternaria. This means that last year 43% of the potatoes in the ground could be classified as susceptible to early blight and so potentially at risk. Virtually all potato varieties grown are susceptible to late blight. Growers will want to protect their potato crops against both blight diseases, by using a fungicide with proven dual activity, such as Dithane,” says David.

He explains that the protectant fungicide mancozeb, as in Dithane NT and Dithane 945, is perceived as the key active against Alternaria in Europe where this disease is more significant. “Dithane is one of the very few fungicides to have label recommendations for both diseases. In the UK there are only a handful of products with either label or EAMU (former a SOLA) approvals for Alternaria alone.”

Rates of use for both mancozeb products against late and early potato blight are 2 kg/ha, both delivering what experts agree is an effective dose for Alternaria activity, (which is 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, says David.

Dr. Stormonth reports that Dithane mancozeb has reached its fifty year anniversary and the current brands, Dithane NT and Dithane 945, have celebrated this milestone after being re-registered by CRD with re-freshed labels, supported by modern up-to-date field data. “It hardly seems possible that mancozeb is 50 years old and yet it is still playing such a vital role in the battle against potato blight right across the world.”

"Over these decades it has seen a huge change in the population and severity of potato blight and it still controls all known strains of late blight, including the newly discovered Green 33. One of its sustaining advantages is its ability to control all blight strains through its multisite activity. It retains its position as the multi-site fungicide and is regarded as the bedrock fungicide when it comes to managing resistance.”

"Of course Dithane has developed and moved on over the last years, not least of which in formulation technology. Compared to the original product, Dithane now has a particularly advanced formulation which redistributes the active on the leaf surface and gives it excellent rainfastness,” says David.