Characterization of a Peanut Leaf Spot of Unknown Etiology

Irregular leaf spot (ILS) of peanut was first noticed in Florida during the late 1990s. By 2000, ILS was apparent throughout much of the southeastern peanut growing region of the United States. Experiments were conducted to identify the cause of ILS, characterize ILS development over time, and evaluate the effect of genotype, tillage, and applications of fungicides and bactericides on ILS. Severities of ILS were near maximum levels at 33 to 42 days after planting (DAP) and in decline by 56 DAP. Incidence of ILS was greater in the lower canopy than the upper canopy. In most cases, ILS intensities were greater in strip-tilled plantings than conventional-tilled plantings and in the peanut breeding line UF-99325 than the cultivar Georgia Green. No fungicide or bactericide treatment suppressed ILS intensity. Attempts to isolate pathogenic fungi or bacteria from ILS lesions were unsuccessful. Although a pathogen cannot be totally dismissed as the cause of ILS, it is likely that ILS is caused by an abiotic factor. Accepted for publication 17 May 2010. Published 27 July 2010.