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Title: EFFECT OF POSTEMERGENCE HERBICIDES ON CERCOSPORA ARACHIDICOLA HORI AND EARLY LEAF SPOT OF PEANUT (REVISE TITLE, ADD ACC. DATE)

Author
item BAYSINGER, J - PIONEER SEEDS
item Melouk, Hassan
item MURRAY, D - OKLAHOMA STATE UNIVERSITY

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Weed and disease management are essential for profitable peanut production. Early leafspot is a common disease of peanut caused by the fungus Cercospora arachidicola Hori. Oklahoma peanut growers and researchers have expressed concern about the possibility of increased early leafspot disease incidence resulting from the use of post emergence herbicides. Knowledge of fthe effect of herbicides on incidence and severity of early leafspot disease will assist growers in making informed decisions for disease control. The objectives of this study were to evaluate the effect of postemergence herbicides on the conidial germination of Cercospora arachidicola Hori, and on the incidence of early leafspot disease in peanut under greenhouse conditions. Conidial germination of the leafspot fungus was significantly enhanced (>100%) by bentazon and imazethapyr, a commonly used herbicide in peanut, at concentrations up to 10,000 mg/L, when compared with the untreated control. Lactofen reduced conidial germination by 23% compared with the control at concentrations as low a 1 mg/L, and completely inhibited germination at concentrations equal to or higher than 5000 mg/L. A concentration of 10,000 mg/L of either acifluorfen or 2,4-DB completely inhibited conidial germination. None of these herbicides increased the incidence and severity of early leafspot on peanut plants when compared with untreated peanuts. In fact, lactofen reduced leafspot incidence 12% and decreased sporulation of lesions 22% compared with the untreated check. All herbicides decreased sporulation except for bentazon and imazethapyr. Peanut plants treated with 2,4-DB alone showed a trend for decreased early leafspot severity.

Technical Abstract: Experiments were conducted to evaluate the effect of postemergence herbicides on the conidial germination of Cercospora arachidicola Hori, and on the incidence of early leafspot disease in peanut (Arachis hypogaea L.) under greenhouse conditions. Conidial germination was significantly enhanced (>100%) at concentrations of up to 10,000 mg/L of bentazon ([3-(1-methylethyl)-(1H)-2,13-benzothiadiazin-4(3H)-one 2,2-dioxide]) and imazethapyr ([2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H- imidazol-2-yl]-5-ethyl-3-pyridinecarboxylic acid]) when compared with the untreated control. Lactofen ([(+/-)-2-ethoxy-1-methyl-2-oxoethyl-5- [2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate]) at 1 mg/L reduced conidial germination by 23% compared with the control, and completely inhibited germination at concentrations =/> 5000 mg/L. Solutions of 2,4-DB ([4-(2,4-dichlorophenoxy)butanoic acid]) had a stimulating effect on conidial germination at concentrations