REDUCTION OF IMAZALIL EFFECTIVENESS AGAINST CITRUS GREEN MOLD IN CALIFORNIA PACKINGHOUSES BY RESISTANT BIOTYPES OF PENICILLIUM-DIGITATUM

Oranges and lemons inoculated with imazalil-sensitive and imazalil-resistant isolates of Penicillium digitatum were dipped in imazalil suspensions in the laboratory or sprayed with water or wax formulations in commercial packinghouses. Dip treatments (1-2 g a.i./L) significantly reduced infection of lemons by resistant biotypes but did not control their sporulation on diseased fruit. Control of infection by resistant biotypes was inferior to that by sensitive biotypes. Commercial packinghouse treatments at 1-4 g a.i./ L (maximum registered dosage) gave poor control of infection by resistant isolates and had no effect on their sporulation on fruit. When biotypes with resistance to both imazalil and thiabendazole were inoculated into lemons, infection was poorly controlled by dip treatment with either or both fungicides.