Foliar anthracnose caused by Colletotrichum gloeosporioides is the most important onion (Allium cepae) disease in Guiricema and Guidoval-MG. Fungicides, mostly benomyl (Ben), are intensively sprayed for disease control but they have been inefficient. We tested the hypothesis of occurrence of resistant isolates of C. gloeosporioides to Ben and compared fungicides for pathogen control. Conidial germination of the isolates decreased as Ben concentration increased and the fungicide completely prevented mycelial growth. For all pathogen isolates tested, disregarding fungicide concentration, methyl thyophanate (MT) + mancozeb (Man), Man, chlorothalonil (Chl), Ben+Man, TM+Clo, captan (Cap), and prochloraz (Pro) inhibited germination. All fungicide treatments but Chl, completely halted mycelial growth. Under greenhouse conditions each treatment was sprayed on onion 'Texas Early Grano 502' (TEG502) plants and the fungus was inoculated 24 h later. The most efficient treatments in reducing disease intensity were MT+Man, MT+Chl, Ben+Man, Man, Cap, Chl, Ben, and Pro. Ben, TM, Pro or Car was sprayed immediately after, or two, four, or six days after pathogen inoculation in plants of TEG502. Ben and Pro were the most efficient when sprayed right after inoculation; no fungicide controlled the disease at the other spray times.
