Non‐target effect of herbicides: I. effect of glyphosate and hexazinone on soil microbial activity. Microbial population, and in‐vitro growth of ectomycorrhizal fungi

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Abstract
The effects of two herbicides, glyphosate (as a 359 g litre−1 SL) and hexazinone (as a 50gkg−1 granule) on soil microbial population, carbon dioxide evolution, and in‐vitro growth of five species of ectomycorrhizal fungi were investigated. Glyphosate at 0–54 and 3.23 kg a.i. ha−1 and hexazinone at 1. 2 and 8 kg a.i. ha−1 did not reduce soil microbial population or carbon dioxide evolution in the long term (6 months). However, there was a significant short‐term (2 months) effect of glyphosate on both fungal and bacterial counts at the 0.54 kg ha−1 treatment. In in‐vitro tests, Cenococcum graniforme. Hebeloma crustuliniforme and Laccaria laccata were more susceptible to both herbicides than was Suillus tomentosus. which was, in turn, more susceptible than Paxillus involutus. The growth of all five ectomycorrhizal fungi was significantly reduced when subjected to concentrations above 50 μl formulation litre−1 (glyphosate) or 50 μg formulation litre−1 (hexazinone).