Graduate Studies

 

First Advisor

Stephen Wegulo

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Plant Pathology

Date of this Version

11-20-2024

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College at the University of nebraska in partial fulfillment of requirements for the degree of Doctor of Philosophy

Major: Educational Studies (Educational Leadership and Higher Education)

Under the supervision of Professor Deryl K. Hatch-Tocaimaza

Lincoln, Nebraska, February 2020

Comments

Copyright 2024, the author. Used by permission

Abstract

Foliar fungal diseases and Fusarium head blight (FHB) are among the major causes of significant yield losses in wheat production, particularly in Nebraska. Resistant cultivars and fungicide applications are common management strategies, but the overuse of fungicides has raised concerns about resistance in Fusarium graminearum populations in Nebraska. This study evaluated the effects of cultivar resistance, fungicide timing and their economic benefits. It also assessed the sensitivity of Nebraska isolates of F. graminearum and F. boothii to a triazole fungicide. In 2022 and 2024, 14 fungicide treatments and a control were arranged in a split-plot experimental design with two winter wheat cultivars, Zenda (moderately resistant) and Wesley (susceptible), as main plots and treatments as sub-plots. Sphaerex (metconazole + prothioconazole) and Aproach (picoxystrobin) were applied once, twice or three times at Feekes growth stages 6 (BBCH 31, first node detectable), 9 (BBCH 39, ligule of last leaf just visible), and 10.5.1 (BBCH 60, beginning of flowering). Results showed significantly higher foliar disease, FHB and fusarium damaged kernels (FDK) in 2022 due to the “wetter” conditions. Wesley had 50% significantly more FDK than Zenda. Treatments applied at Feekes 9 reduced foliar disease by 69% in Zenda and 74% in Wesley. However, net returns were mostly negative for Zenda (79% of the treatments) and positive for Wesley (93% of the treatments). A single application of fungicide on the susceptible cultivar was more profitable, with Aproach leading to 34% higher yields and 36% higher net returns compared to Sphaerex. Therefore, for optimal results, fungicides should be applied at Feekes 9 to control foliar diseases, with single applications on susceptible cultivars under low disease pressure being the most profitable. Fungicide efficacy testing, using mycelial growth assays, on F. graminearum and F. boothii isolates collected from 2007 to 2022 showed that those from 2022 exhibited 39% lower sensitivity to metconazole (triazole). This shift suggests increasing triazole resistance seen in Fusarium isolates in Nebraska, highlighting the need for ongoing monitoring and a holistic management approach.

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