260 Nowak and Peck: Large Oriental Bittersweet Vines and Utility Arboriculture of the oriental bittersweet problem and provide context for management. Specifically, even if re- searchers controlled all the large vines per site, there would still be thousands more small vines to recolonize the released trees. Yet, once a vine is controlled on a tree, it should take many years before a new vine (seedling or sprout) develops fully into a renewed problem on that tree. Since all of the trees with treated vines were still alive, and the range of average ages for the studied vines was between 9 and 38 years, one can expect it will take decades aſter initial vine control before new vines produce the same problem for the same trees. Putz (1991) made a similar observation in his long-standing studies of liana vines around the world. He stated that while most cut liana stumps sprout, the sprouts generally grow slowly and fail to grow back up into the mature forest canopy. In the first year aſter treatment, herbicide treat- ments did reduce sprouting and resulted in higher mortality of treated oriental bittersweet vines com- pared to vines that were cut-only. In both Studies 1 and 2, the lower concentration herbicide treat- ment (26.9% a.i. glyphosate) produced levels of mortality that were effectively the same as the high-concentration herbicide treatment. Average mortality for low- and high-concentration her- bicide treatments in Study 1 was 82% and 91%, respectively, while for Study 2, they were 67% and 67%, respectively. The lower percent mortality in Study 2 may be due to there only being an October treatment. In Study 1, the October treatment had a lower percent mortality than June, yet the same for August—the overall average mortality of Study 1 includes the high percent mortality for June. It is not clear why the June treatment produced a higher mortality rate than August or October in Study 1; this is opposite to what was expected in the study, based on previous work with cut- stump treatment of trees (Ballard and Nowak 2006; Note that the Ballard and Nowak study did not include cutting alone). It may be that cut vines in June have a lowered stored carbon in roots that reduces sprouting numbers, size, and vigor, similar to sprouting patterns observed with trees (Kays and Canham 1991). A similar timing of cut-stump treatment with and without herbi- cides response was observed by Petrice and Haack (2011) for white ash trees. This timing of cutting ©2016 International Society of Arboriculture result in the current study loses some importance as it disappears by the second year aſter treatment. First year results from the current study are supported by two recent non-refereed studies that tested cut-stump herbicide treatments with glypho- sate applied to oriental bittersweet (both studies were found as Master of Science theses). Lynch (2009) conducted a one-year study in West Virginia, U.S., of individual, large (1–5 cm diameter) oriental bittersweet control that included a cut-stump herbi- cide treatment with 50% Accord (26.9% a.i. glypho- sate) applied in July. Vines were climbing trees in a fully-stocked, 55-year-old forest. Sixteen weeks aſter treatment, the cut-stump herbicide treat- ment had only 10% of the vines survive, compared to 60% survival for cut-only treatments. Across all treatments, many vine sprouts were observed to die over that first growing season. Lynch (2009) also described that cut-stump with herbicide treatment and a cut-only treatment had average sprout num- bers of 8 and 20 per treated vine, and average sprout length of 12 cm and 43 cm, respectively, which are similar to the current study. Wooten (2013) stud- ied population-level control in Pennsylvania, U.S., by treating all vines (small and large) on plots with clonally-isolated, tree-climbing oriental bittersweet. Cut stump with glyphosate (GlyphoMate 41®; 41% a.i. glyphosate) was applied to treated vines in July. Total number of vines alive at the end of the first growing season with herbicide treatment was found not to be different than cutting alone. Unfortu- nately, both studies were concluded aſter the first year; therefore, there are no data on a second year of treatment response. As in the current study, a sec- ond year of study may have changed conclusions. In the current study’s second year aſter treatment, herbicide effects were nearly gone—vine cutting alone produced nearly or the same effects as cut- stump treatment with herbicide. Study 1 still had a significant herbicide treatment effect into the sec- ond year, but the increase in percent mortality with herbicides was much lower in Year 2 compared to Year 1. In Year 1, herbicide treatments nearly dou- bled the percent kill (44% versus 86%), but in Year 2 the increase in percent kill was only 8% (92% versus ~100%). In Study 2, percent mortality did not differ among the treatments aſter the second year, averaging 89% across the treatments. While the average percent mortality in the cut-only plots was 70%, this was not
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