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Spread and Increase of Sugarcane Smut in Louisiana. J. W. Hoy, Department of Plant Pathology and Crop Physiology, Louisiana Agricultural Experiment Station, Louisiana Agricultural Center, Louisiana State University, Baton Rouge 70803; M. P. Grisham, Sugarcane Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Houma, LA 70361. Phytopathology 78:1371-1376. Accepted for publication 3 June 1988. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1988. DOI: 10.1094/Phyto-78-1371.

Disease gradients from inoculum point sources and rates of disease increase between seasons were studied in fields of sugarcane naturally infected with smut during a 4-yr period. Sugarcane stools showing smut whips were counted and mapped during plant cane (first-season crop) and subsequent ratoon crops in fields of three cultivars beginning in different years. Smut incidence increased in ratoon crops in some crop cycles but decreased in others. Infections occurring in plant cane were treated as inoculum point sources, and distances from the nearest plant-cane infection to new infections in first ratoon determined disease gradients. Spread of disease occurred to 11.116.5 m. Regression analysis of disease incidence on distance from an inoculum source indicated that log-log and log-linear disease spread models fit the data. Smut spread and increase were affected by an interaction of cultivar infection characteristics, such as the smut recurrence rate in ratoon stools infected as plant cane, the number of smut whips produced by infected stools in each crop-cycle year, the heights of smut whips in relation to the crop canopy, and environmental factors possibly including winter temperatures and rainfall during the infection period.

Additional keywords: Ustilago scitaminea.