Identifying species of the pathogens causing bitter rot disease of apples in Illinois and evaluating effectiveness of potential fungicides for managing the disease

Bitter rot, caused by Colletotrichum spp., is one of the most important fungal diseases of apples in Illinois and worldwide. Field surveys were conducted in 2019, 2020, and 2021 to assess occurrence of bitter rot disease in commercial apple orchards in Illinois. Results showed the incidence of the disease in 14 of 24 orchards, with symptomatic fruit ranging from 0.7 to 63% (mean 20%) in 2019; 20 of 30 orchards, with the symptomatic fruit ranging from 1 to 100% (mean 27%) in 2020; and 21 of 33 orchards, with symptomatic fruit ranging from 0.7 to 100% (mean 20%) in 2021. Fruits with bitter rot symptoms were observed in most of the orchards in central and southern Illinois, whereas most of the orchards in the northern part of the state did not have symptomatic fruit. Incidence of fruit with bitter rot symptoms in Empire, Golden Delicious, Honeycrisp, and Jonathan apples was higher than other apple cultivars. During the surveys, 270 isolates of fungi from the symptomatic fruits of cultivars Braeburn, Cortland, Empire, Fuji, Gala, Golden Delicious, Gold Rush, Granny Smith, Honeycrisp, Jonathan, Jonagold, McIntosh, Red Delicious, and an unknown cultivar from 33 orchards were collected and identified as C. fioriniae (136 isolates from 21 orchards), C. siamense (129 isolates from 19 orchards), and C. chrysophilum (5 isolates from one orchard). Identification of the species was based on the morphological and molecular characteristics of the isolates. Fungicide efficacy trials were conducted in the laboratory and in an orchard with Honeycrisp cultivar at the University of Illinois Fruit Research Farm in Urbana, Illinois during 2019-2021. Bitter rot was the only fruit rot that developed in the untreated plots. Fungicides used included benzovindiflupyr (Aprovia 0.83EC); captan (Captan 80 WDG); fluxapyroxad + pyraclostrobin (Merivon 0.83SC); potassium phosphite (ProPhyt 4.2 SC); thiophanate-methyl (Topsin-M 70WP); trifloxystrobin (Flint Extra 4.05E); and zinc dimethyldithiocarbamate (Ziram 76PDF). Nine treatments were included in each orchard trial. Benzovindiflupyr, captan, and fluxapyroxad + pyraclostrobin prevented bitter rot development in the treated plots.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Acheampong, Festus

Contributors dc:contributor

• Babadoost, Mohammad

• Bitter rot
• apple
• Colletotrichum species
• fungicide efficacy

Statement dc:rights

• Copyright 2022 Festus Acheampong

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/116021

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F116021