Absence of a Role for Absorption, Translocation, and Metabolism in Differential Sensitivity of Hemp Dogbane (Apocynum cannabinum) to Two Pyridine Herbicides

Abstract

Hemp dogbane is sensitive to fluroxypyr and tolerant to clopyralid. Absorption, translocation, and metabolism of clopyralid and fluroxypyr were studied in hemp dogbane to determine if differences in these processes could be responsible for differential sensitivity. In addition, the effect of growth stage on herbicide absorption and translocation was evaluated. The14C-herbicides were applied to the adaxial side of a single leaf located near the midpoint of hydroponically cultured plants. Uptake of fluroxypyr was more rapid than clopyralid. At 72 h after treatment (HAT), fluroxypyr and clopyralid absorption was 62 and 38%, respectively. Clopyralid was much more mobile than fluroxypyr, with 75% of the absorbed14C from14C-clopyralid recovered outside the treated leaf compared to only 45% for fluroxypyr 72 HAT. Relative to fluroxypyr, a higher percentage of14C-clopyralid recovered outside the treated leaf translocated acropetally, especially when plants were treated during the vegetative stage. Treatment during the early reproductive stage increased basipetal and reduced acropetal translocation relative to the vegetative stage. Neither herbicide was metabolized rapidly. Approximately 60 and 90% of the recovered14C was attributable to unaltered fluroxypyr and clopyralid, respectively, 72 HAT. Some differences in absorption, translocation, and metabolism between clopyralid and fluroxypyr exist, but they cannot fully account for differential sensitivity of hemp dogbane to these two herbicides. Differences in activity at the target site may be responsible for differential activity of these herbicides on hemp dogbane.

Absorption, Translocation, and Metabolism of Triclopyr in Rice (Oryza sativa)

“…Lewer and Owen (6) attributed differential selectivity of triclopyr to metabolism. With two related pyridine herbi cides, clopyralid (3,6-dichloro-2-pyridinecarboxylic acid), and fluroxypyr {[(4-amino-3,5-dichloro-6-fluoro-2-pyridinyl)oxy]acetic acid)}, absorption, translocation, and me tabolism could not account for differential selectivity in hemp dogbane (Apocynum cannabinum L.) (7). Although triclopyr has been evaluated for weed control in rice, there is no information on its absorption, translocation, or meta bolism in the crop.…”

Modeling Xenobiotic Uptake and Movement: A Review

“…For example the model predicted 37% absorption of MSMA 24 hour after application which was exactly the percent of MSMA absorbed by Xanthium strumarium (131). Similar equivalency was observed for pesticides such as 2,4-DB (134), bentazon (136), chlorimuron (137), clethodim (138), clopyralid (139), fluroxypyr (140), dicamba (141), haloxyfop-methyl (142), imazapyr (143), thifensulfuron (149) and many other pesticides (Table 3). In some instances the model predicted more than 3 times the amount of xenobiotic absorbed in comparison to the actual absorption.…”

Clopyralid Tolerance in Strawberry and Feasibility of Early Applications in Florida

“…The auxin receptor AFB5, which is a site of action for carboxylic acids but not aryloxyacetates or benzoates, may be missing or mutated in strawberry plants (Walsh et al 2006). Tolerance may also be linked to the strawberry industry’s reliance on propagating physiologically mature daughter plants for transplants, as differential tolerance to 2,4-D based on physiological maturity has been demonstrated (Pazmiño et al 2011). Strawberry leaves exposed to clopyralid generally only experience slight growth malformation such as cupping (Boyd and Dittmar 2015), which may be due to an alternate pathway in the action of auxinic herbicides that stimulates cell expansion (Grossman 2010), and subsequent metabolism may prevent the slower phytotoxic pathway, though further study is required.…”