Impacts to non-target vegetation following herbicide control of the invasive Japanese climbing fern (Lygodium japonicum) in forests of northwest Florida

Background/Question/Methods

Japanese climbing fern (Lygodium japonicum) is a non-native, invasive vine with widespread occurrence throughout the southeastern Coastal Plain. The spread of Japanese climbing fern into forest ecosystems has detrimental implications for a variety of forest products and ecosystem services.  It first invades as scattered individuals, but reproduces prolifically from spores and revegetates from rhizomes.  It can then form thick, tangled mats that deny growing space for ground vegetation and can overtop shrubs and trees.  Herbicides can be an effective control measure for fern, but effects of those treatments on non-target vegetation can be a problem where fern intermingles with desired vegetation.  The objective of this study was to evaluate the effect of chemical control for Japanese climbing fern on non-target forest vegetation.  We tested the effects of glyphosate, imazapyr, and metsulfuron methyl at three rates and in combination in two bottomland hardwood forests and two pine stands in northwest Florida.  We measured percent cover and crown reduction of Japanese climbing fern, other herbaceous vegetation, and woody vegetation before and after treatment.  Phytotoxicity to woody stems was also recorded.  We analyzed percent cover and crown reduction, and mean phytotoxicity of woody stems, using a complete block design in ANOVA.

Results/Conclusions Several herbicide treatments resulted in 80% or greater crown reduction of Japanese climbing fern, including the high rates of glyphosate alone, glyphosate in combination with imazapyr at low rates, glyphosate in combination with metsulfuron methyl at high rates, and three way combinations.  Metsulfuron applied alone was generally least injurious to associated non-target vegetation.  Small seedlings of woody plants draped in Japanese climbing fern were killed or injured significantly more when sprayed with glyphosate, imazapyr, and combinations of these herbicides.  Because southern pine species are tolerant to the herbicide, fewer pine seedlings than hardwoods showed a phytotoxicity response to the imazapyr treatments.   Percent cover of herbaceous vegetation was also reduced by anywhere from 30-80% with glyphosate and imazapyr treatments, though the long-term recovery of those non-target species has yet to be evaluated.  While there are several options for effectively controlling Japanese climbing fern abundance, the selection of which herbicide treatment to use will vary by forest type and site depending on the associated non-target species and the thickness or abundance of the fern.  Glyphosate alone would be most practical where the fern is thick and matted, but where fern drapes over desired vegetation other treatments would be more appropriate.