Southern Rust of Corn: Outline

Distinguishing common rust vs. southern rust

Southern rust is potentially much more destructive

Guidelines to consider in fungicide decisions

Monitor for stalk strength

Uredia of southern rust (upper leaf surface view)

Southern rust (right side) vs. common rust (left)

Upper leaf surface

Lower leaf surface

Images by Alison Robertson, Iowa State University

Courtesy Greg Henson, McLean Co. Extension

Leaf desiccated by southern rust

“Green islands” of southern rust

Courtesy Greg Henson, McLean Co. Extension

Telia of southern rust

“Puccinia pathways” for P. polysora

http://lib.utexas.edu/maps/americas/north_america_ref_2007.pdf

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U.S. corn: susceptible to low levels of resistance

Image at left courtesy Bob Kemereit, Univ. Georgia

Pace of disease progress under worst-case conditions

5-6 weeks: From undetected to substantial damage

2-3 weeks: Can cause substantial damage, if disease is present… …More or less throughout the field

(even at very low levels) …In all levels of the canopy (lower,

middle, and upper)

Days after mid-silk

R2 (blister stage): 10-14 days R3 (milk stage): 18-22 days R4 (dough stage): 24-28 days R5 (dent stage): 35-42 days R6 (physiological maturity): 55-65

days

http://www.agronext.iastate.edu/corn/production/management/growth/yield.html

Watch for loss of stalk strength