Mat-forming vines now constitute half of invasive plant coverage in eastern US forests, with glyphosate being recommended most often for control. This may result in soils becoming drenched due to over-spraying. Non-target effects of glyphosate on germination of forest moss and fern spore banks has not been a research priority and remains underevaluated. Given extensive use of herbicides to control non-native plants in natural areas, this study was conducted to evaluate whether applications of glyphosate and the bioherbicides Scythe (pelargonic acid) and Weed Zap (clove and cinnamon oils) might affect non-target plant diversity by impacting germination of bryophyte and fern spores from woodland soil. Soil collected from an urban forest known to harbor a diverse moss and fern spore bank was sprayed with herbicide and control treatments and allowed to germinate under laboratory conditions and grow for over a year. Species of mosses and ferns were identified and coverage spatial coverage of species was determined and compared among treatments.
Results/Conclusions
Glyphosate sprayed once on forest soil prepared for moss and fern spore germination and growth in the lab had little effect on the number of moss species or their spatial coverage of the soil after a year’s incubation. However, the number of fern gametophytes and sporophytes were lower in glyphosate-sprayed soils. Both bioherbicides reduced the number of moss species and moss growth, but Weed Zap strongly suppressed the germination and growth of widely distributed colonizing species of mosses. Compared with controls, the number of fern gametophytes and sporophytes was greater in Scythe-treated soils, but much lower in Weed Zap-treated soils.
While more studies in different natural areas and with native plant species are needed, if a forest site is suspected to harbor a diverse spore bank, then given the results of this study, we we suggest that natural areas managers consider using a pelargonic acid-containing herbicide, like Scythe, instead of glyphosate or those containing cinnamon and clove oil.