P-135 - Interactive effect of nitrogen fertilization rate and fungicide application on foliar disease intensity and yield of cotton in the Southeast US

Monday, August 4, 2025

3:45 PM - 4:30 PM HST

Location: Exhibit Hall 3

Presenting Author(s)

AC

Arika Carey, MS (she/her/hers)

Graduate Student
University of Florida
Gainesville, FL, FL, USA

Author(s)

GO

George Kelly O'Brien

Agricultural Scientist
University of Florida
Quincy, Florida, United States
JI

Joseph Iboyi

Postdoctoral Research Associate
University of Florida
Quincy, Florida, United States
CM

Cheryl Mackowiak

Associate Professor
University of Florida
Quincy, Florida, United States
RS

Ramdeo Seepaul

Research Assistant Scientist
University of Florida
Quincy, Florida, United States
GA

Gueorgui Anguelov

Agricultural Scientist
University of Florida
Quincy, Florida, United States
RR

Rizwan Rafique

Postdoctoral Research Associate
University of Florida
Quincy, Florida, United States
IS

Ian M. Small, PhD

Associate Professor
University of Florida Institute of Food and Agricultural Sciences, North Florida Research and Education Center, Plant Pathology
Quincy, Florida, United States

Author(s)

SR

Simon Riley

University of Florida

Cotton (Gossypium hirsutum) can be impacted by foliar disease, including target spot (TS) and areolate mildew (AM). These diseases, caused by the fungal pathogens Corynespora cassiicola and Ramulariopsis spp., respectively, can lead to premature defoliation and yield loss. A field experiment was conducted over two growing seasons to evaluate the effects of nitrogen (N) fertilization rate and fungicide treatment on foliar disease progression and yield loss. A randomized complete block design was used to evaluate seven N rate treatments with and without Priaxor® (292 mL ha⁻¹). Cotton ‘DP1646’ seed was planted in May 2023 and 2024 in Quincy, FL. Fungicide was applied during the first and third weeks of bloom. Visual assessments of defoliation, disease incidence and severity of TS and AM were conducted biweekly. A significant interaction between N rate and fungicide on yield was observed in 2023 while only N rate impacted yield in 2024. In 2023, N rate and fungicide significantly affected defoliation, yet no significant interaction was observed. A significant interaction between N rate and fungicide on defoliation was found in 2024. Ongoing exploration of 2023 TS response data suggests more TS and a trend towards fungicide response at the highest two N rates. In 2024, N rate and fungicide significantly affected TS although no interaction was observed. In both years, fungicide significantly reduced AM. This study provides insight into the impacts of key management practices on foliar diseases of cotton.