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Evaluating Fungicide Timing for Leaf Spot Diseases of Wheat and Fungicide Resistance in Pyrenophora tritici-repentis



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Fungal diseases are a major issue in wheat growing areas of the prairies and can result in significant yield losses if left unchecked. Some of the most common diseases affecting wheat are leaf spots, caused by several pathogen species that make up the leaf spotting complex, including tan spot of wheat, caused by Pyrenophora tritici-repentis. The optimal timing to apply fungicide to protect wheat against leaf spots is during the flag leaf stage (ZGS39), however, another disease, fusarium head blight (FHB), is also a major issue in wheat grown in the prairies and is capable of devastating an entire crop. The optimal timing to apply fungicide to control FHB is during anthesis (ZGS60). It is also possible for pathogen species to become insensitive to fungicides over time if they are frequently exposed to the same class of fungicide, especially site specific fungicides such as quinone outside inhibititors (QoI) like pyraclostrobin or demethylation inhibitors (DMI) like propiconazole. It is therefore imperative to limit the amount of fungicide applied to fields to reduce the exposure to pathogens that may lead to insensitivity. The objective of this project was to evaluate the efficacy of applying synthetic fungicides and a biofungicide at two times, flag leaf emergence and anthesis, to determine if application at either of these timings would adequately control leaf spots. Five fungicide products or product combinations were applied at two growth stages, as single or double applications at five locations in 2013 and 2014 using the wheat cultivar Carberry. The results showed that applying fungicide at anthesis stage provided adequate control of leaf spots compared to applying at flag leaf stage. Although applying fungicide at anthesis stage resulted in a higher incidence of leaf spots when disease pressure was high, yield was the same whether fungicide was applied at flag leaf stage or anthesis stage. The second objective of this study was to determine the baseline sensitivity of the Pyrenophora tritici-repentis populations from Alberta and Saskatchewan to two fungicide modes of action, QoIs and DMIs, on spore germination and radial growth on fungicide amended solid agar media. Seventy-one isolates were collected from Saskatchewan in 2013-2014 and AB in 2010 and radial growth measured on V8-PDA media amended with propiconazole, pyraclostrobin and pyraclostrobin with SHAM at five different concentrations. Spore germination was also determined by counting the number of germinated spores in a 5 µL mL-1 spore-water suspension treated with 10 µL of 10x diluted lactophenol. The effective concentration to reduce spore germination by 50% (EC50) values were determined by calculating the number of spores that successfully germinated against the total number of spores. There were also five different fungicide concentrations for the spore germination treatments. The results of the study created a baseline for pyraclostrobin and propiconazole sensitivity and it was determined that QoI and DMI insensitivity has not occurred in the P. tritici-repentis population in Saskatchewan and Alberta.



Plant pathology, spring wheat, Pyrenophora tritici-repentis, fungicide



Master of Science (M.Sc.)


Plant Sciences


Plant Science


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