In vitro sensitivity and field effectiveness of synthetic and plant-based fungicides against dragon fruit canker caused by Neoscytalidium dimidiatum

Dragon Fruit Canker (DFC), caused by Neoscytalidium dimidiatum, threatens the profitability of the dragon fruit industry worldwide. In the U.S., the number of fungicides registered for this crop is limited, challenging the effective control of DFC, particularly in South Florida, where frequent outbreaks occur. This study evaluated the in vitro sensitivity of N. dimidiatum isolates to 13 synthetic and four plant-based fungicides and assessed the efficacy of the most promising candidates on detached fruit and in field trials. The synthetic fungicides fluazinam, fludioxonil, difenoconazole, propiconazole, tebuconazole, and azoxystrobin had the lowest effective concentration values (EC50), ranging from 0.01 μg/ml to 1.48 μg/ml, indicating strong inhibition of mycelial growth in vitro at minimal concentrations. In contrast, the plant-based fungicides thyme oil and garlic oil demonstrated higher EC50 values (35.38 μg/ml and 37.10 μg/ml, respectively) and proved ineffective in preventing DFC symptoms in detached fruit assays. Tebuconazole was one of the most effective chemicals in detached fruit assays, with over 95% efficacy in controlling DFC, but its effectiveness decreased to 50% in the field. Field trials revealed that fluazinam was the most effective fungicide tested, reducing DFC severity in fruits by 93%. Fungicide effectiveness was lower on stems than fruits, with none exceeding 65% efficacy in the field. This is the first study to investigate the sensitivity of N. dimidiatum isolates to multiple fungicides in the U.S. Given its superior performance in field trials, fluazinam is a promising candidate for DFC control and should be considered further for registration in the country.