Control of Johnsongrass Ecotypes

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Abstract
Field experiments were conducted to study the effectiveness of 2,2-dichloropropionic acid (dalapon) for the control of 55 morphologically distinct ecotypes of johnsongrass (Sorghum halepense(L.) Pers.) collected throughout the United States and from several foreign countries. Ecotypes varied widely in their response to dalapon whether collected from Mississippi, from 10 other states, or from eight foreign countries. Initial control of seven ecotypes with dalapon increased 8 to 35% when nitrogen fertilization was increased from 0 to 300 lb/A. Regrowth of surviving plants was more vigorous with increased nitrogen levels so increased fertility reduced final control. Comparative differences in the susceptibility of the seven selected ecotypes to monosodium methanearsonate (MSMA) were not as great as those obtained with dalapon. Varying the rate of nitrogen fertilization had less effect on johnsongrass susceptibility to MSMA than to dalapon. Dalapon controlled sorghum almum (Sorghum almumParodi) better than johnsongrass.