|Efficacy assessment of Demethylation Inhibitor (DMI) fungicides against Guignardia citricarpa, the causal agent of Citrus Black Spot (CBS)|
N. THAPA (1), M. M. Dewdney (1). (1) Citrus Research and Education Center, University of Florida, Lake Alfred, FL, U.S.A.
Copper-based and strobilurin fungicides are the recommended fungicides to manage CBS, a new fungal disease in Florida. DMI fungicides could be a potential alternative mode of action for rotation against CBS. The project objectives are to determine the <i>in vitro</i> fungal population response and the baseline sensitivity to the potentially registered DMIs. Tetraconazole, propiconazole, difenoconazole, fenbuconazole, and imazalil were evaluated in a mycelial growth inhibition assay with various ranges of concentrations for each fungicide. One ml of each stock solution, or water as a control, was mixed with the media to obtain the final concentrations. Inoculated plates were incubated at 24°C, under 12 hr light/dark conditions. The plates were scanned after 2 weeks and mycelial growth area was measured with Image-J. Mycelial growth on amended media was compared to the control. There were three replicates per concentration and the whole experiment was done twice. Regression with 3-parameter sigmoidal curves was used to calculate the half maximal effective concentration (EC50). The mean EC50s for difenoconazole, propiconazole, and tetraconazole were 0.0013, 0.011, and 0.0401 mg/ml, respectively. Preliminary results for the mean EC50s of fenbuconazole and imazalil were 0.0073 and 0.1 mg/ml, respectively. Results obtained from this study will aid the management of CBS and to understand the fungal response pattern towards DMI fungicides.