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Low blight pressure changes control options



The dry weather this spring has meant low potato blight pressure and few confirmed late blight outbreaks so far. With the weather forecast being for continued dry weather, growers are considering their blight options at full canopy stage, with both late and early blight and overall cost of the treatment in mind.

With this prospect, straight mancozeb, as either Dithane 945 or Dithane NT, is now rapidly increasing in demand, as they are low cost but highly effective options, particularly when the weather is border line for late blight infections and Alternaria appears to be the more obvious disease. Opportunities to make cost savings without reducing efficacy should be grabbed with both hands, as production costs increase. Growers shouldnt lose sight of effective disease control, albeit at low incidence, and Dithane has proven to be a strong protectant fungicide, with dual activity on early and late blight, says Dr. David Stormonth, Technical Manager for Interfarm.

We are already picking up reports of early blight (Alternaria) in the field this year, more so than late blight (Phytophthora) : unsurprisingly as the warmer and drier conditions we have experienced so far are more conducive to this disease. Growers will need fungicides with dual activity on these diseases. The protectant fungicide mancozeb is regarded as a key active against Alternaria in Europe and Dithane now has label recommendations for both late and early blight in potatoes in the UK, reminds David.

According to Dr. Stormonth, Dithane is a very cost-effective protectant fungicide, still widely used throughout the UKs crop, even after decades of use. Mancozeb is particularly important as the major multi-site fungicide and is the key element for resistance management in late blight programmes, either as a straight or in co-formulation. There is no known resistance to mancozeb, which is why it is also co-formulated into many blight fungicides to help protect them from resistance problems.

Since its introduction many years ago, the formulation of Dithane has been continuously improved. Advances in production technology and formulation have improved its crop coverage, increased its rainfastness, with reduced dust and improved packaging and reduced operator risk. This mean handling, shelf life properties and product effectiveness have all been significantly improved, says David.

Dithane NT (which stands for Neotec) is a modern WDG formulation that has been re-engineered to make it even more effective. The NT granules are 250 microns in size and are easily dispersed in the spray solution. These granules break down in the solution to smaller, evenly-sized particles of between 1.3-1.5 microns diameter, much smaller than generic mancozeb WDGs, which have particles up to 3 microns in size.

Rates of use for Dithane 945 and Dithane NT are 2 kg/ha, with spray intervals of 7 to 10 days and harvest intervals of 7 days. The maximum number of applications per crop is now 8, giving plenty of scope to use Dithane throughout a full blight control programme.

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