Disease Note

White Rust Epiphytotic on Amaranthus hybridus in South Florida Incited by Albugo bliti. J. P. Gilreath, University of Florida Gulf Coast Research and Education Center, Bradenton 34203. J. B. Jones, University of Florida Gulf Coast Research and Education Center, Bradenton 34203. Plant Dis. 69:542. Accepted for publication 12 February 1985. Copyright 1985 The American Phytopathological Society. DOI: 10.1094/PD-69-542d.

White rust, incited by Albugo bliti (Biv.) Kuntze, has been reported on smooth pigweed (Amaranthus hybridus L.) but not in epiphytotic proportions. In spring 1983, shiny, white to pale yellow, raised pustules (sori) surrounded by chlorotic tissue were observed on the underside of foliage of all smooth pigweed plants at nine locations in Manatee County, Florida, and on the Gulf Coast Research and Education Center’s 81-ha farm. The causal organism was identified as A. bliti. In a pigweed plant population experiment, the number of pustules increased from 3.8 to 7.2 per square centimeter as plant population increased from 26,909 to 215,273 plants per hectare. As disease progressed, heavily infected foliage abscised, reducing biomass yields. Although recent research in Florida indicates smooth pigweed may have potential as a biomass crop, such use in Florida may be restricted by white rust.