Laboratory and field evaluation of efficacy of potential fungicides for managing phytophthora blight (Phytophthora capsici) of processing pumpkin (Cucurbita moschata)

Phytophthora blight, caused by the oomycete Phytophthora capsici Leonian, is a destructive disease that severely limits the production of processing pumpkin (Cucurbita moschata Duchesne). This study was conducted to evaluate the efficacy of the potential eight fungicides or their combinations (cyazofamid, dimethomorph, dimethomorph + ametoctradin, ethaboxam, fluopicolide, mandipropamid, mandipropamid + oxathiapiprolin, and potassium phosphite) for managing P. capsici in the laboratory and fields. The effectiveness of the fungicides on mycelial growth of six Illinois isolates of P. capsici in the laboratory was determined. The field efficacy of the fungicides in fourteen different treatment combinations was evaluated in commercial processing pumpkin fields with high natural inoculum of P. capsici in Tazewell County, Illinois, during 2024 and 2025. The laboratory assays revealed that mandipropamid + oxathiapiprolin (Orondis Ultra) fungicide was the most effective in suppressing mycelial growth of P. capsici isolates [0.0036 µg/ml for 50% reduction in mycelial growth (EC50)]. In field trials, all fungicide treatments significantly (P = 0.05) reduced vine and fruit infection. Incidence of vine infection in control plots was 38.33 and 86.25% in 2024 and 2025, respectively; whereas vine infection in fungicide treated plots ranged from 1.67 to 20.00% and 1.25 to 35.00% in 2024 and 2025, respectively. Fruit infection with P. capsici in untreated plots was 45.40 and 76.10% in 2024 and 2025, respectively. The incidence of fruit infection in the fungicide treated plots ranged from 3.49 to 32.15% in 2024, and from 0.83 to 41.40% in 2025. Spray applications of mandipropamid + oxathiapiprolin (Orondis Ultra) alternated with cyazofamid (Ranman 400SC) alternated with mandipropamid (Revus 2.09SC) resulted in low vine and fruit infection. The findings of this field research emphasized using fungicides with different modes of action for effective protection of processing pumpkins against P. capsici.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Crop Sciences

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Sahil, -

Contributors dc:contributor

• Babadoost, Mohammad

• Oomycetes
• Phytophthora capsici
• Cucurbits

Statement dc:rights

• Copyright 2025 - Sahil

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132592

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132592