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Control of Orange Hawkweed (Hieracium aurantiacum) in Southern Alaska

Published online by Cambridge University Press:  20 January 2017

Steven S. Seefeldt  and
Jeffery S. Conn
Steven S. Seefeldt*
Affiliation:
USDA-ARS, Subarctic Agricultural Research Unit, University of Alaska Fairbanks, Fairbanks, AK 99775
Jeffery S. Conn
Affiliation:
USDA-ARS, Subarctic Agricultural Research Unit, University of Alaska Fairbanks, Fairbanks, AK 99775
*
Corresponding author's E-mail: steven.seefeldt@ars.usda.gov
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Abstract

Orange hawkweed is a perennial European plant that has colonized roadsides and grasslands in south-central and southeast Alaska. This plant is forming near-monotypic stands, reducing plant diversity, and decreasing pasture productivity. A replicated greenhouse study was conducted in 2006 and repeated in 2007 to determine the efficacy of six herbicides (aminopyralid, clopyralid, picloram, picloram + chlorsulfuron, picloram + metsulfuron, and triclopyr) 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 nontarget native vegetation. In the field, only aminopyralid at 105 g ae ha−1 (0.1 lb ae ac−1) and clopyralid at 420 g ae ha−1 controlled orange hawkweed consistently, with peak injury observed 1 yr after treatment. Control with clopyralid was slightly less than that provided by aminopyralid at all observation times, except at Homer, AK, in 2007, where there was a near-monotypic stand of orange hawkweed, and clopyralid did not remove all orange hawkweed plants. Aminopyralid controlled clover (Trifolium spp.), seacoast angelica (Angelica lucida), arctic daisy (Chrysanthemum arcticum), common hempnettle (Galeopsis tetrahit), and willow (Salix spp.) in 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 nontarget species with most recovering the year after treatment. In a pasture system, where grasses are preferred to forbs and shrubs, aminopyralid has an advantage because it controls a broader array of forbs compared with clopyralid. In natural areas, where the desire to retain biodiversity and the aesthetics of multiple forb species mixed with grasses and willows is preferred, clopyralid will leave greater species diversity than aminopyralid.

Keywords

AminopyralidchlorsulfuronclopyralidmetsulfuronpicloramtriclopyrOrange hawkweed, Hieracium aurantiacum L. HIEAUarctic daisy, Chrysanthemum arcticum L. CHYARclover, Trifolium spp.common hempnettle, Galeopsis tetrahit L. GAETEseacoast angelica, Angelica lucida L. ANLUwillow, Salix spp.Alaskaexotic weedsgreenhousenonindigenous plantweed control
Type
Research
Information
Invasive Plant Science and Management , Volume 4 , Issue 1 , March 2011 , pp. 87 - 94
Copyright
Copyright © Weed Science Society of America 

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References

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