Evaluation of Fungicides, Biofungicides, and Plant-Based Extract for the Management of Stem Canker Caused by Botryosphaeria dothidea in Eastern Redbud (Cercis canadensis)

Canker disease, caused by the fungal pathogen Botryosphaeria dothidea , poses a threat to redbud ( Cercis sp.) production in Tennessee, yet effective management strategies are lacking. The objective of this study was to evaluate the efficacy of various fungicides, biofungicides, and a plant-based extract for managing Botryosphaeria stem canker on eastern redbuds in the greenhouse. This study evaluated six fungicides [mefentrifluconazole (Avelyo), didecyldimethylammonium chloride (KleenGrow), two doses of triticonazole + pyraclostrobin (Pillar), difenoconazole + pydiflumetofen (Postiva), ningnanmycin (SP2700), and SP2478, which is an experimental product], three biofungicides [ Ulocladium oudemansii strain U3 (BotryStop), Trichoderma harzianum strain T-22 + T. virens strain G-41 (RootShield PLUS), and Bacillus amyloliquifaciens strain F727 (Stargus)], and a plant-based extract [thyme oil (Tril-21)]. Two trials were conducted from Jun to Dec in 2023 and 2024. Fourteen treatments, including a nontreated inoculated control, a nontreated noninoculated control, and a wound-only control, were arranged in a completely randomized design with six replications for each treatment. One-year-old container-grown eastern redbuds were wounded and artificially inoculated with fungal mycelial plugs, and the treatments were applied on a weekly or biweekly basis. Plant height, width, lesion length, and pathogen recovery were assessed for 6 months. All tested fungicides, biofungicides, and the plant extract lowered canker lesion length and pathogen recovery compared with the nontreated inoculated control. The most effective products for reducing Botryosphaeria canker lesion length and pathogen recovery were Ulocladium oudemansii strain U3, Trichoderma harzianum strain T-22 + T. virens strain G-41 applied as a wound treatment, and triticonazole + pyraclostrobin applied as a foliar treatment. No significant differences were observed in plant height and width among the treatments. These findings provide nursery growers with effective management options for controlling stem canker caused by B. dothidea in redbud production.