Flutriafol as a Promising Fungicide for the Management of Laurel Wilt in Avocado Production

Laurel wilt is a lethal disease caused by Harringtonia lauricola, a nutritional symbiont of several ambrosia beetles. Disease management in avocado orchards relies on cultural practices, as the effectiveness of the only approved fungicide, propiconazole, is limited. To identify additional fungicides, 10 active ingredients from four different FRAC groups were evaluated to establish their effective concentrations for inhibiting pathogen growth by 50% (EC 50 ) and 95% (EC 95 ). Based on their EC 95 values (<2.5 ppm) and known mobility attributes, fungicide formulations containing flutriafol, mefentrifluconazole, prothioconazole + tebuconazole, and tetraconazole were selected for in planta assays. Propiconazole was included as a control. Potted avocado plants (15 months old) were soil-drenched with each fungicide using two concentrations (1× = 2,400 ppm and 3× = 7,200 ppm) administered in three applications, 2 weeks apart. Two weeks after the last application, half of the fungicide-treated plants were inoculated with a spore suspension (1 × 10 7 spores/ml) of H. lauricola. After 35 days, only the plants drenched with distilled water (nontreated control) and one plant in the 1× mefentrifluconazole treatment showed characteristic external symptoms of the disease. Harringtonia lauricola was not recovered from plants treated with flutriafol or propiconazole, whereas one replicate in each of the other treatments yielded the pathogen. Residue analysis of stem tissue showed that flutriafol had the highest concentration, exceeding 300 ppm in the 3× treatment, whereas mefentrifluconazole had the lowest concentration, not exceeding 4 ppm. This study provides evidence to support further testing of flutriafol-based formulations in the management of laurel wilt under field conditions.