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

2 Corn Rusts Tropical Physopella zeae Southern Puccinia polysora Common Puccinia sorghi

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

Upper and lower leaf surfaces

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

Photo by Snook Pataky, Univ. of Illinois

ipmPIPE for southern corn rust scr.ipmpipe.org

Real-time PCR to test for spores in rainwater Images from USDA-ARS Cereal Rust Laboratory

“Puccinia pathways” for P. polysora ?

Southern corn rust Bob Kemerait, Univ. of Georgia

U.S. corn: susceptible to low levels of resistance Image at left courtesy Bob Kemereit, Univ. Georgia

Corn acreage planted in Mexico

Corn acres planted, Lower Mississippi Valley

Alice Robert’s race differential set for P. polysora

Collaboration with USDA Cereal Rust Laboratory to develop DNA-based diagnostics for corn rusts

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): days R3 (milk stage): days R4 (dough stage): days R5 (dent stage): days R6 (physiological maturity): days

Watch for loss of stalk strength