Garden centre sales of such chemicals decreased by 3.1 per cent, according to the report.
There was some growth in pest and disease products, increasing by 6.6 per cent to £44m. However, weedkiller products showed a nine per cent decline, dropping to £43m, thus altering the balance between the two sides of the market. Average prices for weedkillers rose by five per cent - however, this was not enough to prevent the value erosion across the market.
A GfK representative blamed last season's poor weather, which demonstrated that weedkiller sales were weather-dependent.
Sales began strongly, rising by 44.8 per cent from January to April, but the summer's heavy rainfall led to a four per cent drop.