Evaluation for the Potential of a New Fungicide Pyrimethanil for Postharvest Diplodia Stem-end Rot Control on Florida Citrus Fruit

Postharvest decay is one of the most important factors affecting fresh citrus fruit quality and marketing values. Fungicide application is an important measure to achieve effective citrus postharvest disease control. Pyrimethanil is a newly registered fungicide for postharvest use in citrus. The effectiveness of pyrimethanil for the control of diplodia stem-end rot (caused by Lasiodiplodia theobromae) on Florida citrus fruit was evaluated. Pyrimethanil moderately suppressed the mycelial growth of L. theobromae in vitro on potato dextrose agar. The simulated drench test of pyrimethanil on 'Fallglo' tangerine hybrids naturally infected by L. theobromae showed that pyrimethanil at 1000 ppm reduced diplodia stem-end rot incidence by 40.3%, while the standard postharvest fungicides imazalil (1000 ppm) and thiabendazole (1000 ppm) reduced it by 83.1% and 96.7%, respectively. A simulated commercial packingline application test of pyrimethanil (1000 ppm) using 'Pineapple' oranges indicated that pyrimethanil reduced diplodia stem-end rot incidence by 29.4%, while imazalil and thiabendazole reduced it by 70.7% and 84.0%, respectively. Overall evaluation results indicated that pyrimethanil actively reduced the diplodia stem-end rot, but it was less effective compared to the existing postharvest fungicides imazalil and thiabendazole.