Sensitivity of western Canadian <i>Pyrenophora teres</i> f. <i>teres</i> and <i>P. teres</i> f. <i>maculata</i> isolates to propiconazole and pyraclostrobin

<p><i>Pyrenophora teres</i> f. <i>teres</i> (<i>Ptt</i>) and <i>Pyrenophora teres</i> f. <i>maculata</i> (<i>Ptm</i>), the causal agents of the net and spot forms of net blotch of barley, respectively, can be managed in western Canada with fungicides containing propiconazole and pyraclostrobin. Given the potential for development of fungicide resistance, the sensitivity of a collection of <i>Ptt</i> and <i>Ptm</i> isolates to propiconazole and pyraclostrobin was evaluated using microtitre plate bioassays. The concentration of propiconazole needed to inhibit fungal growth by 50% (EC₅₀) was 1.5 mg L⁻¹ for <i>Ptt</i> and 2.3 mg L⁻¹ for <i>Ptm</i>, while the EC₅₀ of pyraclostrobin was 0.015 mg L⁻¹ for <i>Ptt</i> and 0.024 mg L⁻¹ for <i>Ptm</i>. Subsequently, 39 <i>Ptt</i> and 27 <i>Ptm</i> isolates were screened with discriminatory doses of 5 mg propiconazole L⁻¹ and 0.15 mg pyraclostrobin L⁻¹. Inhibition of growth as a result of propiconazole was 12–95% for <i>Ptt</i> and 48–92% for <i>Ptm</i>; growth inhibition as a result of pyraclostrobin was 40–100% and 24–100%, respectively. Two <i>Ptt</i> isolates were insensitive to propiconazole, while one <i>Ptm</i> isolate was insensitive to pyraclostrobin. The latter also showed decreased sensitivity to propiconazole. The identification of net blotch isolates insensitive to these fungicides emphasizes the need for farmers to employ integrated crop management strategies to avoid fungicide resistance build-up.