262 Nowak and Peck: Large Oriental Bittersweet Vines and Utility Arboriculture in full sun (Greenburg et al. 2001; Ellsworth et al. 2004), it may be less shade tolerant throughout its life than reported. In the current study, higher den- sity of small oriental bittersweet along the forest edge versus interior supports the notion that orien- tal bittersweet is less than shade tolerant, and may possibly be shade intermediate. It is known that oriental bittersweet reproduces better as seedlings, sprouts, and root suckers in forest gaps, old field and clearcuts, and open forest edges (Fike and Niering 1999; Silveri et al. 2001; Londré and Schnitzer 2006), indicating that when vine-invaded systems and vines themselves are disturbed, regeneration is successful in areas with increased sunlight. A key aspect of the current study may be that the vines were treated without disturbing the forest. It is expected that if both vines and the subject trees and forests were dis- turbed, long-term treatment effects may have been different; specifically, herbicide use may have been shown to produce added kill and control of oriental bittersweet populations because more of the sprouts would have stayed alive in the cut-only treatment. CONCLUSIONS AND RECOMMENDATIONS Based on two years of field study, researchers con- clude that it may not be necessary to apply herbi- cide via cut-stump methods to kill large oriental bittersweet vines (where large means vines that >2–3 cm in diameter) in areas where the invaded trees and forest systems are not significantly dis- turbed. Cutting alone of vines whose stumps re- mained in full shade resulted in >95% kill across the study plots, excluding the one northern plot in Study 2 with only 20% kill and vines averaging 2.9 cm diameter. Herbicide treatments resulted in nearly 100% kill, but this result was not statistically different from the percent kill with cutting alone. The recommendation to not use herbicides to kill large, cut-stump treated vines is in contrast with published recommendations. Hutchinson (1992) is oſten a cited source for using cut-stump herbicides to kill oriental bittersweet vines (e.g., see citation in Williams and Timmins 2003; Webster et al. 2006), with a recommendation to use a 100% Roundup mix (glyphosate herbicide similar in rate to the high- concentration herbicide treatment in the current study) on cut vine surfaces late in the growing season (just aſter late frost). But, this and other like recom- ©2016 International Society of Arboriculture mendations in the literature are apparently not based on field research. Discovering published literature full of recommendations to cut-stump treat oriental bittersweet vines with herbicides that is not founded in research and the scientific method highlights the importance of conducting long-term herbicide research in support of vegetation management. Results from the current study can be imple- mented immediately and across the range of ori- ental bittersweet. The recommendation to not use herbicides in conjunction with cut-stump methods to kill oriental bittersweet may apply only to large vines whose cut stumps are in shade aſter treat- ment. Large vines are defined as having a mini- mum, near-ground stem diameter of 2–3 cm. These vines are usually twining around large trees, grow- ing up into the canopy, and causing problems to tree health. While many management guidelines include cut-stump treatment with herbicide to kill tree climbing oriental bittersweet vines, it seems that these guidelines are anecdotal and not based on rigorous research as used in the current study. Current study results likely do not apply to smaller oriental bittersweet, particularly those small, trailing, shrub-like vines that are commonly abundant in old fields and mowed roadside rights- of-way. These small vines oſten look like small tree or shrub seedlings, and with populations observed with over 100,000 stems per ha (C. Nowak, per- sonal observation). It may be that persistent mowing or foliar herbicides may be needed to con- trol these younger oriental bittersweet populations. Various other woody vines native to North America can cause problems for vegetation manag- ers similar to oriental bittersweet, but most promi- nent is wild grapevines (Vitis spp.). Research on control of wild grapevines in context of forestry was conducted in the eastern United States over the past five decades. Trimble and Tyron (1979) synthesized earlier research and produced management guide- lines for cut-stump treatments for grape similar to the current study with oriental bittersweet. In gen- eral, Trimble and Tyron (1979) reported that cut grapevines under forest canopies produced sprouts that died in three years, but if the overstory was removed, then the grape sprouts thrived. They rec- ommended severing grape vines growing in well- stocked stands as an effective and inexpensive way to eliminate them, and that this method works
July 2016
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