Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/30/2010
Publication Date: N/A
Technical Abstract: Several hawkweed species from Europe have escaped ornamental planting and have colonized roadsides and grasslands in south central and southeast Alaska. These plants form near monotypic stands, reducing plant diversity and decreasing pasture productivity. A replicated greenhouse study was conducted in 2006 and repeated in 2007 to determine efficacy of 6 herbicides for orange hawkweed control. Based on results of the greenhouse trials, replicated field studies were conducted at two sites each year in 2007 and 2008 with three rates each of aminopyralid and clopyralid to determine efficacy of orange hawkweed control and impacts on non-target native vegetation. In the field, only aminopyralid at 105 g ai/ha and clopyralid at 420 g ai/ha controlled orange hawkweed consistently, with peak injury observed one year after treatment. Aminopyralid controlled clover, wild celery, daisy, brittlestem hempnettle, and willow from the treated areas. Other plant species such as grasses and some annual forbs recovered or increased following control of the hawkweed. Clopyralid had less impact on non-target species with most recovering the year after treatment. In a pasture system, where grasses are preferred to forbs and shrubs, aminopyralid has an advantage as it controls a broader array of forbs compared to clopyralid. In natural areas, where the desire to retain biodiversity and the aesthetics of multiple forb species mixed with grass and willows is preferred, clopyralid will leave greater species diversity than aminopyralid.