Arboriculture & Urban Forestry 42(4): July 2016 used to readily kill woody plants, particularly with later season treatments (Ballard and Nowak 2006). Two replicated field experiments were estab- lished in New York State’s Hudson Valley to deter- mine the effects of cutting and cut surface herbicide treatments with glyphosate on mortality of large oriental bittersweet vines. Based on work with trees (e.g., see Ballard and Nowak 2006), it was hypothe- sized that Accord® herbicide [active ingredient (a.i.): glyphosate] (Dow AgroSciences, Indianapolis, Indi- ana, U.S.) applied to freshly cut bittersweet stumps would result in significant mortality of treated vines, and that percent kill would be greatest with the highest concentration of glyphosate applied late in the season, as compared to no herbicide or low con- centrations applied earlier in the growing season. A randomized block factorial experiment at one site and a randomized block experiment across three sites were established during the 2011 growing sea- son and treatment effects measured in summer 2012 and autumn 2013, effectively one and two growing seasons aſter treatment. Patterns of mortality and sprouting in the first year following treatment sup- ported the hypothesis that glyphosate herbicide can increase the amount of kill and reduce sprout num- bers and growth, but surprisingly, early-summer treatments with herbicides were more efficacious than autumn treatments. At the end of the second growing season aſter treatment, differential treat- ment effects disappeared—vine mortality was high across all treatments, leading to a conclusion that her- bicides may not be needed to achieve a high degree of control of large, cut, oriental bittersweet vines. METHODS AND MATERIALS Study Areas Study plots were laid out along field/forest edges on the National Park Service’s Vanderbilt National Historic Site in Hyde Park (Study 1, and one block of Study 2) (41°47’35”N, 73°56’35”W), and along roadside ROWs near the village of Lake George (43°25’45”N, 73°43’15”W), and just outside New York City near the towns of Stony Point (41°16’55”N, 73°57’41”W for one treatment plot) and East Fish- kill (41°34’23”N, 73°46’48”W for two treatment plots). Field/forest edges were studied because it is known that bittersweet is commonly abundant along these forest edge sites (Robertson et al. 1994; 255 Merriam 2003; Londré and Schnitzer 2006). Elec- tric transmission line ROWs produce extensive lengths of forest edge, which is why oriental bitter- sweet is an important problem for utility foresters, as well as other arborists and vegetation managers. The study areas were located entirely within the Hudson Valley Section of the Eastern Broad- leaf Forest Province and Hot Continental Division (Section 221B) (McNabb and Avers 1994). Across the Hudson Valley, average annual precipitation is 102 cm, average annual temperature ranges from 7°C to 10°C, and the growing season lasts from 160 to 180 days (McNab and Avers 1994). These envi- ronmental conditions are conducive to the spread, growth, and persistence of oriental bittersweet (Dukes et al. 2009). The northern site (Lake George) is apparently near the current northern distribu- tion of oriental bittersweet in New York State, and the southern sites (East Fishkill and Stony Point) are near to where oriental bittersweet may have entered into New York (just north of New York City). Soils associated with the study sites included Dystrochrepts and Fragiachrepts with udic mois- ture and mesic temperature regimes in the southern and middle areas of the section, and Hapludalfs with udic moisture and mesic temperature regimes in the north. Soil series were all excessively well-drained and apparently included (Natural Resources Con- servation Service 2014): Hinckley soils in the Lake George block, a Nassau-Cardigan complex of soils in the Hyde Park blocks, an unidentified Udor- tent associated with a pit-quarry operation on one south block plot (Stony Point), and Hoosic soils in the other two south plots (East Fishkill). Soils in the Lake George and the Stony Brook plots appeared to be anthropic, as the landforms had apparently been reworked with heavy machinery during highway construction and maintenance. Experimental blocks associated with both studies were fully-stocked forests that ranged in age from 40 to 80 years (C. Nowak, personal observation). The forest types were as expected for the Hudson Valley—various combinations of northern hardwoods and Appalachian oaks. The most important tree species across the study areas were sugar maple (Acer saccharum), tree-of- heaven (Ailanthus altissima), black locust (Rob- inia pseudoacacia), and red oak (Quercus rubra) for the Hyde Park site, and flowering dogwood ©2016 International Society of Arboriculture
July 2016
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