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Size really does matter, says Dow

When it comes to protectant fungicide formulations and their particle sizes, then size really does matter, but in this instance the smaller, the better, according to Dow AgroSciences.

"Smaller particles have a greater surface area to volume ratio and so give greater leaf coverage. The protectant fungicide, Dithane NT (New Technology), has been re-engineered and contains only small and evenly sized particles of between 1.3-1.5 microns diameter, whereas other generic mancozeb dispersible granules have particles of 1.7 to 2.7 microns. Laboratory tests show that a generic DG formulation of mancozeb provides 160 particles per square millimetre and Dithane NT provides nearly three times as many, with 440 particles per square millimetre. The significance of the consistently smaller mancozeb particles in Dithane NT is that they get caught onto the leaf more easily, cover the target surface more effectively and stick better to the plant than larger particles. The Dithane NT particles also have a zinc – rich shell surrounding an EBDC core and so release the mancozeb at a slow and controlled rate. The superior formulation results in better suspensibility in the spray solution, better coverage of the crop, better rainfastness, and so better and longer lasting overall protection. Better engineered formulations of mancozeb such as Dithane NT are worth the small premium, compared to their poorer generic look alikes." said Nick Gooch, Marketing Specialist for Dow AgroSciences.

"The differences can be seen quite easily between dispersible granule formulations, but are much more fundamental between formulation types - for example one wettable powder formulation tested was found to have particles of 2.3 to 3.4 microns. This is two or three times larger than Dithane NT. The same generic wettable powder formulation of mancozeb was shown to cover a square millimetre of leaf with only 110 particles, which is only 25% of the particles provided by Dithane NT. These WP formulations will give less coverage, will be less efficient and much less rainfast than Dithane NT." added Gooch.

Dithane NT is recommended in potatoes for the control of potato blight, in oilseed rape for the reduction of downy mildew, in wheat for the reduction of Septoria, brown rust and sooty moulds and in winter barley for the reduction of Rhynchosporium and sooty moulds. It contains 75% mancozeb formulated as a New Technology water dispersible granule. The standard rate for Dithane NT in potatoes is 1.7 kg/ha, with a higher rate of 2 kg/ha when blight risk is high. It has spray intervals of 7,10 or 14 days and the harvest interval of 7 days. In terms of practicality, Dithane NT has no LERAP restrictions and no restrictions on the number of sprays per crop. As a multi-site fungicide, it is a vital product to integrate into any anti-resistance disease control programme.