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The Effect of Selected Herbicides on CO₂ Assimilation, Chlorophyll Fluorescence, and Stomatal Conductance in Johnsongrass (Sorghum halepense L.)

Jason A. Ferrell, Hugh J. Earl and William K. Vencill
Weed Science
Vol. 51, No. 1 (Jan. - Feb., 2003), pp. 28-31
Stable URL: http://www.jstor.org/stable/4046621
Page Count: 4
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Effect of Selected Herbicides on CO₂ Assimilation, Chlorophyll Fluorescence, and Stomatal Conductance in Johnsongrass (Sorghum halepense L.)
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Abstract

Greenhouse studies were initiated to determine the duration of time after herbicide treatment required to render johnsongrass physiologically noncompetitive. Nicosulfuron, imazapic, clethodim, and glyphosate were applied to rhizomatous johnsongrass at 35, 70, 140, and 840 g ai ha⁻¹, respectively. Net carbon assimilation, stomatal conductance, chlorophyll meter readings, and maximum (dark adapted) efficiency of photosystem II were measured. Net carbon assimilation (A N) was assumed to be the best indicator of johnsongrass competitiveness. Johnsongrass was considered to be physiologically noncompetitive when A N declined below 50% of that of non-treated check. From these data, it was concluded that glyphosate rendered johnsongrass noncompetitive most readily, 4.3 d after treatment, whereas no differences were detected between nicosulfuron, imazapic, or clethodim throughout the experiment. Stomatal conductance (g s) was highly correlated to A N and was determined to be an adequate substitute for A N when determining johnsongrass competitiveness. It was concluded that chlorophyll meter readings and photosystem II efficiency were poor indicators of johnsongrass competitiveness.

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