Identification and Chemical Control of Stem Canker Pathogen of Idesia polycarpa

<i>Idesia polycarpa</i> is an important woody oilseed tree crucial for ensuring China's grain and oil security. The expansion of <i>I. polycarpa</i> plantations has been accompanied by an increase in pests and diseases, with canker disease recently observed in two forests in Henan Province. Field surveys revealed a disease incidence of 70.12% among 328 surveyed trees, indicating a substantial threat to plantation health. The most virulent pathogen, strain SQ5, was identified as <i>Botryosphaeria dothidea</i> through molecular sequencing and morphological analyses. Strain SQ5 showed an optimum growth temperature of 25 °C and a mycelial lethal temperature of 60 °C. The pathogen thrives in acidic conditions and is promoted by light, with the ability to utilize various carbon and nitrogen sources. In vitro toxicity assessments identified four effective fungicides: 70% thiophanate-methyl (EC50 = 0.0169 µg/mL), 43% tebuconazole (EC50 = 0.0219 µg/mL), 20% octylamine acetate (EC50 = 0.0271 µg/mL), and 40% difenoconazole (EC50 = 0.0954 µg/mL). Field trials demonstrated that 43% tebuconazole (average efficacy = 35.29%) and 40% difenoconazole (average efficacy = 23.53%) exhibited superior control of <i>I. polycarpa</i> canker. This study represents the first systematic analysis of <i>I. polycarpa</i> canker and its control measures, laying a foundation for further research and field management strategies. Given the significance of <i>I. polycarpa</i> in Chinese forestry, this underscores the need for effective management strategies to sustain its productivity and mitigate risks associated with expanding plantations.