Evaluation of broadcast and spot herbicide applications for narrowleaf goldenrod [Euthamia graminifolia (L.) Nutt.] management in lowbush blueberry

Goldenrods are common perennial weeds in lowbush blueberry fields in Nova Scotia. Management options are limited to mowing and suppression with POST mesotrione applications. The objectives of this research were to (1) compare efficacy of single versus sequential nonbearing-year POST mesotrione applications on goldenrod (2) identify the optimal interval between sequential POST mesotrione applications (3) evaluate nonbearing-year POST bicyclopyrone applications on goldenrod, and (4) evaluate nonbearing-year summer and fall herbicide spot treatments on goldenrod. POST mesotrione applications at 144 g ai ha(-1) caused 39% to 77% injury but did not reduce goldenrod shoot density. In contrast, mesotrione applications at 144 g ai ha(-1) followed by sequential mesotrione application at 14, 21, or 28 days after initial treatment caused greater than 90% injury to goldenrod and reduced both nonbearing- and bearing-year shoot density. POST bicyclopyrone applications at 50 g ai ha(-1) caused 69% to 80% injury to goldenrod but did not reduce shoot density. A bicyclopyrone plus mesotrione tank mixture did not improve goldenrod control relative to mesotrione or bicyclopyrone alone. Summer spot applications of glyphosate (7.24 g ae L water(-1)), glufosinate (0.75 g ai L water(-1)), and mesotrione (0.72 g ai L water(-1)) consistently injured goldenrod and reduced both nonbearing- and bearing-year shoot density. Summer spot applications of bicyclopyrone (0.25 g ai L water(-1)), flazasulfuron (0.31 g ai L water(-1)), dicamba (1 g ae L water(-1)), dicamba plus diflufenzopyr (0.7 g ae L water(-1) plus 0.3 g ai L water(-1)), triclopyr (1.68 g ai L water(-1)), clopyralid (0.08 g ai L water(-1)), tribenuron methyl (0.2 g ai L water(-1)), and foramsulfuron (0.2 g ai L water(-1)) injured goldenrod but did not consistently reduce shoot density. When these herbicides were evaluated as fall spot applications, only glyphosate reduced goldenrod shoot density in the year after application.