Identification and Chemical Control of Stem Canker Pathogen of Idesia polycarpa

Idesia polycarpa is an important woody oilseed tree crucial for ensuring China's grain and oil security. The expansion of I. polycarpa 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 Botryosphaeria dothidea 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. polycarpa canker. This study represents the first systematic analysis of I. polycarpa canker and its control measures, laying a foundation for further research and field management strategies. Given the significance of I. polycarpa in Chinese forestry, this underscores the need for effective management strategies to sustain its productivity and mitigate risks associated with expanding plantations.