CONTROL OF ALTERNARIA BROWN SPOT OF MINNEOLA TANGELO WITH FUNGICIDES

Field experiments to control fruit lesions of Alternaria brown spot (A lternaria alternata pathovar citri) of Minneola tangelo (Citrus reticu lata 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 lesi ons when sprayed four or five times at 2 week intervals, beginning sho rtly after full bloom in April. Additional iprodione applications in t he summer or autumn did not provide any substantial improvement. When disease severity was moderate, a spray volume of 1500 1 ha(-1), applie d by an air-blast sprayer, was adequate; however, when disease was sev ere, 3000 1 ha(-1) was required. Metiram (0.2 g a.i. 1(-1)) and a copp er, mancozeb and iron cyanide mixture (Tri Miltox forte) (0.35 g l(-1) product) also were effective in preventing fruit infection. These fun gicides, as well as copper hydroxide, were used successfully in altern ation with iprodione, in management strategies intended to delay devel opment of resistance to iprodione by A. alternata pv. citri. Tank mixe s at two-thirds of the regular rate of iprodione and metiram or Tri Mi ltox forte also performed well. The following fungicides were ineffect ive 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.