Control of Alternaria brown spot of Minneola tangelo with fungicides

Field experiments to control fruit lesions of Alternaria brown spot (Alternaria alternata pathovar citri) of Minneola tangelo (Citrus reticulata x C. paradisi) were conducted over a period of 5 years. Iprodione at 0.5 g a.i. 1(-1) was consistently effective in reducing fruit lesions when sprayed four or five times at 2 week intervals, beginning shortly after full bloom in April. Additional iprodione applications in the summer or autumn did not provide any substantial improvement. When disease severity was moderate, a spray volume of 1500 1 ha(-1), applied by an air-blast sprayer, was adequate; however, when disease was severe, 3000 1 ha(-1) was required. Metiram (0.2 g a.i. 1(-1)) and a copper, mancozeb and iron cyanide mixture (Tri Miltox forte) (0.35 g l(-1) product) also were effective in preventing fruit infection. These fungicides, as well as copper hydroxide, were used successfully in alternation with iprodione, in management strategies intended to delay development of resistance to iprodione by A. alternata pv. citri. Tank mixes at two-thirds of the regular rate of iprodione and metiram or Tri Miltox forte also performed well. The following fungicides were ineffective in controlling Alternaria brown spot: procymidone, difenconazole, tebuconazole, fluazinam, maneb, captan, chlorothalonil, prochloraz Mn, and a mixture of prochloraz Zn and folpet. (C) 1997 Elsevier Science Ltd.