Absorption, Translocation, and Degradation of Tebuthiuron and Hexazinone in Woody Species

McNeil, W. K.; Stritzke, J. F.; Basler, Eddie

doi:10.1017/s0043174500059919

Cited by 19 publications

(16 citation statements)

References 15 publications

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“…Both tebuthiuron and hexazinone are metabolized into demethylated and hydroxylated products in plants (Eaton et al, 1976;Martina et al, 1981;McNeil et al, 1984;Fischer and Michael, 1995). These metabolites were not measured in this study.…”

Section: Resultsmentioning

confidence: 99%

“…day" 1 , respectively, to coca leaf chewers (U.S. Department of State, 1990). However, the percent of root-absorbed tebuthiuron or hexazinone translocated to the leaves is species dependent (Seinert and Stitzke, 1977;McNeil et al, 1984;Holt, 1981;Sidhu and Feng, 1993). Therefore, estimates of residues in coca plants based on uptake and translocation data for other plant species would be unreliable.…”

Section: Herbicide Residues In Leaves Of Erythroxylvm Coca Var Coca Pmentioning

confidence: 99%

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Herbicide residues in leaves of Erythroxylvm coca var coca plants treated with soil-applied tebuthiuron and hexazinone

Lydon

Darlington²

1998

J. of Env. Sc. & Hlth., Part B

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The herbicide residue levels in leaves of Erythroxylum coca var. coca Lam. plants treated with soil applications of tebuthiuron and hexazinone at 3.36 and 6.72 kg a.i. ha-1 were determined in order to estimate the potential for human exposure to these residues from consuming the leaves or cocaine produced from them. Field-grown plants were treated with a commercial formulation of tebuthiuron or hexazinone and leaves were harvested at the first indication of herbicide injury (i.e. chlorosis and/or necrosis) and at the onset of leaf abscission. Herbicide residues were detected by HPLC in leaf samples from both harvests of all plants treated with tebuthiuron or hexazinone. At 3.36 kg ha-1, herbicide residues in the leaves were less than 2 micrograms g-1 dry wt. for both harvests of both experiments. The highest residue levels detected were 5.90 micrograms g-1 dry wt. for tebuthiuron and 7.17 micrograms g-1 dry wt. for hexazinone in leaves from plants treated with the herbicide at the rate of 6.72 kg ha-1 and harvested at the onset of leaf drop. Based on published toxicity data and estimates of leaf consumption, the herbicide residues in leaves of E. coca var. coca plants treated with tebuthiuron or hexazinone at twice the recommended control rates or less would have a negligible contribution to the health risks of individuals who chew coca leaves. Furthermore, based on the most conservative estimates of cocaine yield and herbicide carry over, death by cocaine overdose would occur long before the NOEL for either herbicide was reached.

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Section: Resultsmentioning

confidence: 99%

Section: Herbicide Residues In Leaves Of Erythroxylvm Coca Var Coca Pmentioning

confidence: 99%

Herbicide residues in leaves of Erythroxylvm coca var coca plants treated with soil-applied tebuthiuron and hexazinone

Lydon

Darlington²

1998

J. of Env. Sc. & Hlth., Part B

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“…We did not determine if established field-grown plants also maintain this two-fold differential in root;foliage ratio. Differences in uptake and translocation have been implicated in differential tolerance of other woody species to soil-applied hexazinone (McNeil et at., 1984;Barron & Monaco, 1986), although root structure was not discussed.…”

Section: Resultsmentioning

confidence: 99%

“…Older plants of R. hispidus were found to absorb and translocate four times as much '"C-label to the foliage than P. melanocarpa, and this was related to a greater root: foliage ratio of the sensitive species. Greater uptake has been attributed to the sensitivity of some species of hexazinone (McNeil et al, 1984;Barron & Monaco, 1986) and other 1,3,5-triazine herbicides (Shone & Wood, 1972;Werner & Putnam, 1980).…”

Section: Resultsmentioning

confidence: 99%

Uptake and metabolism of hexazinone in Rubus hispidus L. and Pyrus melanocarpa (Michx.) Willd

Jensen¹,

Kimball²

1990

Weed Research

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Summary: Rooted cuttings of Pyrus melanocarpa (Michx.) Willd. had a 3.5‐fold greater tolerance to soil‐applied hexazinone than those of Rubus hispidus L. in a greenhouse trial. R. hispidus accumulated four times more 14C‐label in the foliage following root uptake of 14C‐hexazinone than P. melano‐carpa. Here, the greater uptake and susceptibility of R. hispidus was related to its greater root:fol‐iage (weight) ratio compared to the tolerant P. melanocarpa. However, in whole plant metabolism studies employing younger plants there were no differences in 14C accumulation in the leaves. Here 14Chexazinone was converted to a number of hydroxylated and/or demethylated triazinone metabolites in both species following vacuum infiltration into leaf disks and root sections, or following root uptake in whole plants. A major difference in metabolism between the two species was the greater formation of the mono demethylated metabolite, B, [3‐cyclohexyl‐6‐methylamino‐l‐methyl‐l,3,5‐triazine‐2,4‐dione] in P. melanocarpa which may also contribute to its greater tolerance. A loss of total 14Clabel from all plant parts with time may reflect cleavage of the 14C‐ring‐labelled herbicide.

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“…This results in a build-up of triplet state chlorophyll which generates singlet oxygen (Dodge, 1982) that peroxidize cell membrane lipids and the affected plant dies from oxidative stress (Balke, 1987;Bartels, 1987). Some species can metabolize the compound before it reaches the chloroplasts (McNeil et al, 1984;Jensen and Kimball, 1990), thereby imparting some degree of tolerance. While blueberries are fairly tolerant (Zutter and Zedaker, 1988), oaks, sweetgum (Liquidambar styraci¯ua) and sumac (Rhus spp.)…”

Section: Site History and Experimental Treatmentsmentioning

confidence: 99%

Restoring longleaf pine wiregrass ecosystems:

Brockway

Outcalt

2000

Forest Ecology and Management

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A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wild®re, was treated with applications of hexazinone (1.1 or 2.2 kg/ha) in May 1991. All applications successfully reduced competition from oaks in the overstory and understory (mortality >80%), resulting in progressive increases in the foliar cover of wiregrass, all graminoids and forbs through time. Broadcast application caused a decline in forb cover and species richness during the initial growing season, which recovered by the following year. The 2.2 kg/ha spot application resulted in an increase in species richness, while evenness declined with the continuing expansion of wiregrass. The entire site was then burned in June 1995 by prescribed ®re, which caused a widespread decrease in the cover of oaks, shrubs, wiregrass, all graminoids and forbs and plant species richness. In the following year, forb cover increased and oak cover remained signi®cantly lower on plots treated with the combination of hexazinone plus ®re than on ®re-only plots. The overall cover of forbs, graminoids, shrubs and longleaf pines continued to increase through time. Broadcast application initially exposed a greater number of understory plants to direct contact with herbicide, posing a higher mortality risk than may be acceptable in restoration efforts. Although recovery occurred in subsequent years, the lower selectivity of broadcast application makes it a less suitable restoration technique. Spot application of hexazinone was more selective in its effects upon the plant community. The 2.2 kg/ha spot application produced increases in the cover of wiregrass, all graminoids and forbs and the highest levels of species richness and diversity. The 2.2 kg/ha application rate was also most effective in controlling woody plant competition and is therefore recommended for restoring longleaf pine wiregrass ecosystems in sandhills and similar environments. Hexazinone application followed by prescribed ®re accelerates the rate of ecosystem restoration over that achievable by using ®re alone. The ecological bene®ts of controlling competition and rebalancing¯oristic composition rapidly achieved through this combination of treatments would likely require many cycles of prescribed ®re, if used as an individual treatment, over a period of several decades.

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Absorption, Translocation, and Degradation of Tebuthiuron and Hexazinone in Woody Species

Cited by 19 publications

References 15 publications

Herbicide residues in leaves of Erythroxylvm coca var coca plants treated with soil-applied tebuthiuron and hexazinone

Herbicide residues in leaves of Erythroxylvm coca var coca plants treated with soil-applied tebuthiuron and hexazinone

Uptake and metabolism of hexazinone in Rubus hispidus L. and Pyrus melanocarpa (Michx.) Willd

Restoring longleaf pine wiregrass ecosystems:

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