The invention relates to the formulation of deltamethrin as water-dispersible granules(WDG) which comprise wetting agents, dispersants, solid inert substances and one or more acids in an amount sufficient to adjust the pH of the mixture to a value in the range from 1 to 7. The granules are particularly useful for controlling animal pests.

Deltamethrin(S-α-cyano-3-phenoxybenzyl-(1R,3R)-3-(2,2-dibromovinyl)-2,2 -dimethylcyclopropanecarboxylic acid ester) is an insecticide from the class of the pyrethroids and has been used extensively and for a long time for controlling pests (C. D. S. Tomlin, The Pesticide Manual, 11th Edition, British Crop Protection Council, Farnham 1997).

Numerous formulations have been disclosed, including suspension concentrates(SC), which have the advantage that they do not require any organic solvents. Other solvent-free formulations are water-dispersible granules (WDG) which, when added to water, give a suspension of the deltamethrin particles in water, similarly to suspension concentrates(SC).

EP-A 0 224 845 describes, in a general manner, water-dispersible granules(WDG) for use in crop protection. A relatively large number of possible active compounds is listed, including deltamethrin. However, an example of a deltamethrin-containing formulation is not given.

Surprisingly, it has now been found that certain WDG formulations of deltamethrin have, on application, considerably better activity than the suspension concentrates(SC) which are usually used.

In addition to the components described, the formulations according to the invention may comprise further components customary in the formulation. Examples are antifoams, such as dialkylpolysiloxanes, for example Rhodorsil 416® (Rhodia, France), binders, such as polyvinyl alcohol, for example Mowiol 383® (Clariant, Germany), preservatives, such as benzoic acid or sorbic acid, or other customary adjuvants.

Thus, water-dispersible granules(WDG) are prepared by the extrusion process, usually by mixing the active compound with the formulation auxiliaries and an inert material, subsequent dry grinding of this mixture (not required if the starting material particles are fine enough), moistening this powder with a suitable amount of water and subsequent compacting of the material in an extruder. Granules produced in this manner are dried and, if appropriate, comminuted or fractioned to give granules of a suitable size.