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1 April 2006 Foliar vs. Root Sensitivity of Hairy Bittercress (Cardamine hirsuta) to Isoxaben
GLENN WEHTJE, CHARLES H. GILLIAM, MICHAEL E. MILLER, JAMES E. ALTLAND
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Abstract

It has been previously reported that POST-applied isoxaben can effectively control established hairy bittercress. Experiments were conducted to determine the relative importance of root vs. foliar entry of POST-applied isoxaben. At a common isoxaben rate of 0.56 kg/ha, foliar-only and foliar plus soil applications provided 10.5 and 23.3% control, respectively, as determined by fresh weight reduction. In contrast, soil-only application provided 47.0% control. Hairy bittercress foliar absorption of 14C–isoxaben did not exceed 15% of the amount applied after 72 h. Therefore, the comparatively less effectiveness of foliar-only applications may be attributed primarily to limited absorption. Minimal isoxaben concentration required to inhibit root growth of hydroponically grown hairy bittercress was 0.0025 mg/L. Higher concentrations were required to produce a response in the foliage. Sorption of isoxaben by pine bark rooting substrate, typical of what is used in container nursery production, exceeded 99% of amount applied after 36 h. Even with 99% sorption, the probable concentration within the aqueous phase remains sufficient to inhibit hairy bittercress root growth. Additional studies with 14C–isoxaben established that approximately 35% of the root-absorbed isoxaben was translocated into the foliage. Translocation from the roots into the foliage was reduced to 16% when the experiment was repeated during environmental conditions less favorable for vegetative growth (i.e., longer day length and higher temperature). Results indicate that the control of hairy bittercress with POST-applied isoxaben is likely the result of root absorption and root-growth inhibition. Expression of phytotoxicity within the foliage is also a component, but is dependent upon the root-absorbed isoxaben being translocated into the foliage. Extent of this translocation is dependent upon plant maturity and prevalent environmental conditions.

Nomenclature: Isoxaben; hairy bittercress, Cardamine hirsuta L. #3 CARHI.

Additional index words: Herbicide sorption, hydroponics, organic rooting substrates.

Abbreviations: Kd, distribution coefficient.

GLENN WEHTJE, CHARLES H. GILLIAM, MICHAEL E. MILLER, and JAMES E. ALTLAND "Foliar vs. Root Sensitivity of Hairy Bittercress (Cardamine hirsuta) to Isoxaben," Weed Technology 20(2), 326-333, (1 April 2006). https://doi.org/10.1614/WT-05-054R1.1
Published: 1 April 2006
JOURNAL ARTICLE
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