THE RUST OUTBREAK OF 2000:WHAT'S GOING ON

Authors: HOY, JEFF - LSU AGRICULTURAL CTR; Grisham, Michael; HOLLIER, CLAYTON - LSU AGRICULTURAL CTR

Submitted to: Sugar Bulletin
Publication Type: Trade Journal
Publication Acceptance Date: 8/1/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rust, caused by the fungus Puccinia melanocephala, is a sugarcane disease that has been present in Louisiana for more than 20 years, although it has generally been of minor importance. However, during Spring 2000, a widespread outbreak occurred throughout the Louisiana industry. This was particularly alarming to growers since it occurred in the dominant variety, ,LCP 85-384. Several factors appear to have favored the development of thi outbreak. The mild temperatures, dry days and regular dew formation at night that occurred this spring favored rust development. During most winters in Louisiana, above ground sugarcane tissue is killed by cold temperatures. Since the rust fungus can only survive from season to season on green plant tissue, the mild winter of 1999-2000 in which all green tissue was not killed favored the survival of the fungus and the production of vast quantities of spores for new infections in the spring. Because LCP P85-384 previously showed little rust development, the possibility that a new race of rust has developed also exits. As summer temperatures increase above the optimum for spore production, we expect the incidence of rust to decline. Rust is a highly visible disease, and it is natural for growers to become concerned when they see it in their major variety. However, considering average weather conditions in Louisiana, the usual progression of the disease, and examples from other industries, the chances are that rust will continue to be a disease of minor importance.

Technical Abstract: Sugarcane rust, caused by Puccinia melanocephala, has been present in Louisiana for more than 20 years, although it has generally been of minor importance. However, during Spring 2000, an epidemic occurred throughout the Louisiana industry in the dominant variety, LCP 85-384. Several factors appear to have favored the development of this outbreak. During most winters in Louisiana, the above ground sugarcane tissue is killed by cold temperatures. Since P. melanocephala is an obligate parasite, the mild winter of 1999-2000 in which all green tissue was not killed favored the survival of the fungus and the production of vast quantities of spores for new infections in the spring. Mild temperatures, dry days and regular dew formation at night in the spring also favored rust development. Because LCP 85-384 was previously rated resistant to rust, the possibility that a new race of rust has developed also exits. Research in literature and previous observations in Louisiana suggest that as summer temperatures increase above the optimum for spore production the incidence of rust will decline. Rust is a highly visible disease, and it is natural for growers to become concerned when they see it in their major variety. However, considering average weather conditions in Louisiana, the usual progression of the disease epidemic, and examples from other sugarcane industries, we predict that rust will continue to be a disease of minor importance in Louisiana.