Pathogen Species Causing Brown Rot of Peaches in Illinois and Efficacy of Fungicides for Managing the Disease Harrison Seitz1, Andrew N. Miller2, and Mohammad Babadoost1 1Department of Crop Sciences, University of Illinois, Urbana, IL 61801, USA; and 2Illinois Natural History Survey, University of Illinois, Champaign, IL 61820, USA Brown rot is one of the important diseases of peaches in Illinois. This study was conducted to: (i) identify pathogen species causing brown rot disease in commercial peach orchards in Illinois, and (ii) evaluate the efficacy of fungicides for managing the disease. Results of orchard surveys showed 9 of 14, 4 of 8, and 6 of 13 orchards had symptomatic brown rot fruits in 2020, 2021, and 2022, respectively. No blossom blight or shoot blight was observed. Symptomatic fruits were collected from eight peach cultivars throughout the state and the associated fungi were isolated. Based on the cultural characteristics and sequences of the ITS region, 127 of 129 collected isolates were identified as Monilinia fructicola, and two isolates as M. laxa. Fungicide sensitivity of M. fructicola isolates was conducted in the laboratory against azoxystrobin, captan, fenhexamid, trifloxystrobin, penthiopyrad, difenoconazole cyprodinil, fluopyram tebuconazole, fluopyram trifloxystrobin, fluxapyroxad pyraclostrobin, propiconazole, and thiophanate-methyl. The EC50 of azoxystrobin, captan, and penthiopyrad for the colony development of the isolates were significantly (P = 0.05) higher than the other fungicides tested. Field trials were conducted on ‘Redhaven’ and ‘Contender’ peaches for two years to evaluate efficacy of the commercial product of the above-mentioned fungicides. Trees were sprayed with fungicides at 10- and 14-day intervals. Luna Experience 3.34SC (fluopyram tebuconazole), Luna Sensation 4.20SC (fluopyram trifloxystrobin), and Merivon 4.18SC (fluxapyroxad pyraclostrobin) were the most effective fungicides for managing brown rot and other summer diseases of peach.
