Dominic Dyer is stepping down as chief executive of the Crop Protection Association (CPA) after four-anda-half years.
He said he intends to pursue new opportunities in the non-governmental and charitable sectors. Dyer's replacement is due to be announced by the end of July.
Meanwhile, the CPA's statistical review for 2011 shows a five per cent rise in herbicide, insecticide and fungicide sales to £621.5m.
Communications manager Wendy Gray said new members, including Gowan and Interfarm, as well as new products, accounted for the rise.
"Garden and household sales are stable, but we expect figures to be down for 2012 because of the wet weather, although that will help slug control sales," she added.
She said a 10 per cent fall in the amenity market was down to hard surface products becoming unavailable because of EU regulation.
Agricultural and horticultural herbicides, fungicides and insecticides sales rose six per cent to £552.6m. Some 18,211 tonnes of active ingredients were used, up by 16 per cent.
Garden and household product sales were flat at £53.7m, with herbicides one per cent down at £35m and insecticides nine per cent down at £6m.
Inorganic herbicides at £3.8m and fungicides at £8.4m were five and four per cent up respectively. The tonnage of active ingredients used was up by one per cent to 4,868.
Industrial and amenity sales fell by 10 per cent to £15.7m with fungicides down 36 per cent to £2.5m and other uses including ferrous sulphate down 62 per cent to £342,000.