The effects of Velpar L (hexazinone) on seedling growth and ectomycorrhizal symbiosis of Pinusresinosa

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Abstract
We investigated the effects of velpar L (hexazinone) on ectomycorrhizal (Laccaria laccata) and nonmycorrhizal Pinus resinosa seedlings in the greenhouse and in the field. In both greenhouse and field studies, seedling growth was reduced by Velpar L at 1, 2, and 4 kg/ha application rates in the short term (2 months'' exposure) with significant recovery occurring afterwards. Seedling mortality occurred only with herbicide treatments and was higher in the greenhouse than in the field. The 4 kg/ha velpar L treatment mycorrhizal (Laccaria laccata inoculated) seedlings. In both experiments mycorrhizal infection was significantly reduced by 2 and 4 kg/ha velpar L treatments during the 0- to 2-month and 2- to 6-month exposure periods, with significant recovery occurring in the latter. Although seedlings not infected with Laccaria laccata became mycorrhizal through unidentified indigenous species, their infection rates were also affected by velpar L at all levels during the 0- to 2-month period and at the 2 and 4 kg/ha levels after 2-6 months of exposure to the herbicide.