An investigation into the differential response of hemp dogbane (Apocynum cannabinum L.) to two pyridine herbicides
Orfanedes, Michael S.
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https://hdl.handle.net/2142/19565
Description
Title
An investigation into the differential response of hemp dogbane (Apocynum cannabinum L.) to two pyridine herbicides
Author(s)
Orfanedes, Michael S.
Issue Date
1990
Doctoral Committee Chair(s)
Wax, Loyd M.
Department of Study
Crop Sciences
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Language
eng
Abstract
Field and laboratory experiments were conducted to study the differential effects of fluroxypyr and clopyralid herbicides on hemp dogbane (Apocynum cannabinum L.). In field experiments, fluroxypyr provided excellent control of hemp dogbane while the response to clopyralid was very poor. Good season long control of hemp dogbane was obtained with postemergence application of fluroxypyr at rates as low as 140 g ai/ha. In certain situations, control four and eight weeks after application was superior when application was made during the early reproductive growth stage as opposed to the vegetative growth stage. Twelve months after treatment, fluroxypyr provided 65 to 75 percent control of regrowth. Clopyralid treatments at this time were not significantly different than controls.
Laboratory studies revealed that both herbicides are readily absorbed and translocated in hemp dogbane. Absorption of fluroxypyr occurred faster and to a greater extent than clopyralid. Of that absorbed, more clopyralid than fluroxypyr was translocated from the treated leaf and apical translocation of clopyralid was greater than fluroxypyr. Both herbicides exhibited similar patterns of basipetal movement. Basipetal translocation was slightly greater when herbicides were applied during the early reproductive growth stage relative to the vegetative growth stage. More fluroxypyr than clopyralid was metabolized. However, neither compound was rapidly metabolized and with both herbicides, nearly 50% or more of recovered $\sp{14}$C remained as parent compound 72 and 144 hours after treatment. Some differences in absorption, translocation, and metabolism of fluroxypyr and clopyralid have been shown. However, the magnitude of these differences is relatively small and make it unlikely that any of these processes can account for the extreme differential sensitivity of hemp dogbane to fluroxypyr and clopyralid herbicides.
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