|Rusness Jr, Donald|
Submitted to: Pesticide Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 19, 1995
Publication Date: N/A
Interpretive Summary: Leafy spurge is a noxious perennial weed introduced into North America from Eurasia in the 1800's. Leafy spurge has now invaded much of the range land in the North Central region of the United States and it is rapidly expanding its range. There is no economically effective herbicide for the control of this weed. Since cattle avoid infested areas, leafy spurge causes severe economic impact. Quinclorac is a new herbicide registered for use in rice and turf grass which was recently shown to be effective in the control of leafy spurge. This manuscript reports on the uptake, movement, toxicity and detoxification of quinclorac in leafy spurge. The purpose of the study was to provide information that would be useful in selecting the methods of application and use of quinclorac for leafy spurge control or to suggest ways that the herbicide might be modified for improved performance in leafy spurge. It was shown that quinclorac toxicity to leafy spurge was increased 24-fold if the foliage of the plant was removed before treatment. It was also shown that a major factor limiting the effectiveness of quinclorac in leafy spurge control was the ability of leafy spurge to excrete the herbicide from the plant via the roots. Less important factors that limited leafy spurge toxicity in leafy spurge were detoxification and sequestration.
Technical Abstract: [14C]Quinclorac in the presence of a surfactant was readily absorbed through the leaves of leafy spurge. After foliar application, ca. 20% of the quinclorac became sequestered in the treated leaves. The remainder of the quinclorac was translocated basipetally and acropetally. The young leaves and apex were the strongest sinks for quinclorac. Although quinclorac was translocated to the roots, it was effluxed rapidly from the roots into the soil. Quinclorac was also taken up by the roots and translocated acropetally. It was metabolized to a C-1 glucose ester that was converted subsequently to a pentosylglucose ester (major product) or a malonylglucose ester (minor product). Quinclorac was metabolized at a rate of 1 nmole/g tissue/hr in the young leaves. Quinclorac was toxic to leafy spurge when applied to the leaves (LD50 2.0 Kg/ha), the soil (LD50 1.7 Kg/ha), or to both the leaves and soil (LD50 1.0 Kg/ha). The activity of soil-applied quinclorac was increased 24-fold when the shoots were cut-off at the soil level prior to treatment (LD50 0.07 Kg/ha). Symptoms were typical of an auxenic herbicide.