Sensitivity of Cercospora sojina isolates to quinone outside inhibitor fungicides

Guirong Zhang, Dianne K. Pedersen, Daniel V. Phillips, Carl A. Bradley

Research output: Contribution to journalArticlepeer-review


Frogeye leaf spot, caused by Cercospora sojina, causes yield reductions to soybean (Glycine max) grown worldwide. Quinone outside inhibitor (QoI) fungicides have been effective in managing frogeye leaf spot, but the risk of selecting C. sojina strains with resistance to this class of fungicides is considered high. A QoI fungicide resistance monitoring program was initiated, in which sensitivities to azoxystrobin, pyraclostrobin, and trifloxystrobin were determined in C. sojina isolates collected prior to QoI fungicide use on soybean (baseline group) and C. sojina isolates collected from soybean fields in 2007, 2008 and 2009. For the baseline group, the mean effective fungicide concentration at which 50% of the conidial germination was inhibited (EC 50) was determined to be 0.01287, 0.00028 and 0.00116 μg ml -1 for azoxystrobin, pyraclostrobin and trifloxystrobin, respectively. When mean EC 50 values of 2007, 2008 and 2009 C. sojina isolates were compared to baseline C. sojina EC 50 values, a small but statistically significant (P ≤ 0.05) shift towards less sensitivity was observed for trifloxystrobin in 2009. Although small (<1.5-fold), this shift in sensitivity indicates a risk of selecting for C. sojina strains with reduced sensitivity to QoI fungicides, and fungicide sensitivities should continue to be monitored in the future.

Original languageEnglish (US)
Pages (from-to)63-68
Number of pages6
JournalCrop Protection
StatePublished - Oct 2012


  • Cercospora sojina
  • Frogeye leaf spot
  • Glycine max
  • Soybean
  • Strobilurin

ASJC Scopus subject areas

  • Agronomy and Crop Science


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