Identification and Chemical and Biological Management of Fusarium Root and Crown Rot Disease of Oakleaf Hydrangea

Oakleaf hydrangea ( ) is an important ornamental plant grown in Tennessee. In May 2018, after late spring frost, cultivars Pee Wee and Queen of Hearts showed root and crown rot symptoms and identification and management of the disease was a major concern. The objective of this research was to identify the causal organism of this disease and develop management recommendations for nursery growers. Isolates from the infected root and crown parts were subjected to microscopy and the morphology of fungi resembled . Molecular analysis was conducted by amplifying the internal transcribed spacer (ITS) of ribosomal DNA, beta-tubulin (b-Tub), and translation elongation factors 1-α (EF-1α) regions. was identified as a causal organism based on morphological and molecular analysis. Pathogenicity test was done to complete the Koch's postulates by drenching containerized oakleaf hydrangea with conidial suspension. Experiments were conducted to evaluate different chemical fungicides and biological products with different rates for Fusarium root and crown rot management in container grown 'Queen of Hearts'. Plants were inoculated by drenching containerized oakleaf hydrangea with 150 mL conidial suspension of maintaining the concentration of 1×10 conidia/mL. Root and crown rot were assessed using a scale of 0-100%. Recovery of was recorded by plating root and crown sections. Chemical fungicides such as mefentrifluconazole (BAS75002F), the low rate (1.09 mL/L) of difenoconazole + pydiflumetofen (Postiva), and the high rate (1.32 mL/L) of isofetamid (Astun) and biopesticide: the high rate (1.64 g/L) of ningnanmycin (SP2700 WP) effectively reduced Fusarium root rot severity and pyraclostrobin effectively reduced Fusarium crown rot severity in both trials.