Masters Theses

Date of Award

12-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Heather Kelly

Committee Members

Sebe Brown, Tyson Raper

Abstract

Areolate Mildew (ARM) is a new/reemerging disease in the United States. ARM can be caused by two pathogens, Ramulariopsis gossypii and R. pseudoglycines. In the 2022 growing season, ARM was observed for the first time in Tennessee. The objectives for this research were to evaluate the distribution of ARM in West Tennessee and how ARM develops in different planting practices. Additionally, an economic analysis of planting practices and their correlation to yield and a break even analysis on a fungicide application was conducted. To investigate the prevalence of ARM in West Tennessee, commercial fields were surveyed in 2022, 2023, and 2024. Symptoms of ARM were observed in nine counties in West Tennessee; specifically 26 fields on 8 different varieties. Observations of ARM in West Tennessee led to the development of field trials evaluating ARM in different planting patterns (solid and 2x1 skip) and row spacings (76 and 97 cm). In 2023 and 2024, yield, disease incidence, and severity were measured. Additionally in 2024 plant height, canopy closure, and defoliation were measured. In 2023, the 97 cm row spacing treatment had significantly more disease incidence and severity than the narrower spacing. Similarly, in 2024 greater severity was observed in the 97cm, 2x1 skip treatment compared to the 97 cm solid planted cotton, although disease severity was relatively low in 2024. Even with greater disease the 97 cm row, solid planted treatments outyielded all other treatments in 2023 and the wider row spacing outyielded the narrower row spacing and no differences were seen in planting patterns in 2024. These greater yields also influenced greater PNR in comparison to all other treatments, where 97 cm, solid planting in 2023 and the wider spacing in 2024 had greatest PNR. No differences were seen in PNR among planting patterns. Depending on the price received for seed cotton and the price of fungicide, it was determined that the protected yield needed to break even on a fungicide application ranged from 219- 374 kg ha-1. In general, greater disease was observed in wider row spacing although the same treatments provided the greatest yield and partial net returns (PNR), indicating while increased air movement and microclimate in wider rows increased disease, there was still not enough disease development to impact yield.

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