The effectiveness of herbicides for management of tor-grass (Brachypodium pinnatum s.l.) in calcareous grassland

Abstract

Calcareous grasslands are highly biodiverse semi-natural habitats. A particular challenge to European calcareous grassland management in recent years has been the increasing dominance of the competitive grass Brachypodium pinnatum. B. pinnatum is difficult to control by traditional means but selective herbicides offer a potential alternative.We trialled five selective herbicides on two levels of B. pinnatum cover (sparse and dense) at a UK calcareous grassland site over three years of repeated treatment. We compared the effect of herbicides with a minimal intervention treatment (cutting) and current management practices (cutting and grazing for sparse cover, broad-spectrum glyphosate application for dense cover) on the cover of B. pinnatum, key indicator species and the composition of the grassland community.Areas with initially sparse B. pinnatum showed no significant reduction under any herbicide, whilst some herbicides (propyzamide, cycloxydim) showed detrimental impacts on non-target species. Cutting and grazing showed some beneficial effects, despite no significant reduction in B. pinnatum.On areas of dense B. pinnatum cover, glyphosate application reduced cover of B. pinnatum but led to colonisation by negative indicators or species typical of agricultural situations and disturbed ground. None of the selective herbicides significantly reduced dense B. pinnatum cover, and some (propyzamide, tepraloxydim, fluazifop-P-butyl) had significant negative impacts on non-target species.Our results suggest herbicide treatments, including glyphosate, are unlikely to offer long-term control of B. pinnatum on calcareous grasslands. A more promising approach is suggested by the effect of cutting and grazing, although further experimentation is required to determine the most effective regimes.