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The effect of selected herbicides on CO2 assimilation, chlorophyll fluorescence, and stomatal conductance in johnsongrass (Sorghum halepense L)

Published online by Cambridge University Press:  20 January 2017

Jason A. Ferrell ,
Hugh J. Earl  and
William K. Vencill
Jason A. Ferrell
Affiliation:
Department of Crop and Soil Sciences, University of Georgia, Athens, GA 30602
Hugh J. Earl
Affiliation:
Department of Crop and Soil Sciences, University of Georgia, Athens, GA 30602
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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 (AN) was assumed to be the best indicator of johnsongrass competitiveness. Johnsongrass was considered to be physiologically noncompetitive when AN declined below 50% of that of nontreated 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 (gs) was highly correlated to AN and was determined to be an adequate substitute for AN when determining johnsongrass competitiveness. It was concluded that chlorophyll meter readings and photosystem II efficiency were poor indicators of johnsongrass competitiveness.

Keywords

Clethodimglyphosateimazapicnicosulfuronjohnsongrass, Sorghum halepense L., SORHAChlorophyll meterchlorophyll fluorescencegas exchangenet carbon assimilationstomatal conductance
Type
Research Article
Information
Weed Science , Volume 51 , Issue 1 , February 2003 , pp. 28 - 31
Copyright
Copyright © Weed Science Society of America 

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