Graduate Studies, UNL

 

Dissertations and Doctoral Documents from University of Nebraska-Lincoln, 2023–

First Advisor

Gary Hein

Second Advisor

Jeffrey Bradshaw

Degree Name

Doctor of Plant Health (D.Pl.H.)

Committee Members

Brett Lynn, Brian Wardlow, Temra Jackson-Ziems

Department

Plant Health

Date of this Version

2025

Document Type

Dissertation

Citation

A dissertation presented to the faculty of the Graduate College of the University of Nebraska in partial fulfillment of requirements for the degree Doctor of Plant Health (D.Pl.H.)

Major: Plant Health

Under the supervision of Professor

Lincoln, Nebraska, December 2025

Comments

Copyright 2025, the author. Used by permission

Abstract

Monitoring plant health, including nutritional status assessment, is an important component of crop management decisions. This doctoral document addresses the use of agricultural remote sensing through focused investigations of plant disease detection and nutrient status assessment technologies that advance precision agriculture. The first chapter provides a comprehensive overview of remote sensing technologies in agriculture and examines current capabilities, limitations, and future directions. The final two chapters address studies that evaluated the virus-nitrogen interaction in wheat and compared methods to determine the nitrogen status of midseason field corn.

The first study evaluated the wheat streak mosaic virus (WSMV) × nitrogen interaction in early growth stage winter wheat. It integrated traditional plant pathology assessments with hyperspectral remote sensing to identify nitrogen levels that either suppress or exacerbate WSMV symptoms and virus titer and determine which vegetation indices better detect the interactive effects of nitrogen and virus infection. It was observed that adequate nitrogen partially maintained chlorophyll levels in infected plants and delayed symptom development. The Chlorophyll Red Edge (Clred_edge) index demonstrated the best sensitivity in detecting virus × nitrogen interactions. Under sufficient or high nitrogen supply, Clred_edge detected spectral changes associated with virus presence before visible symptoms became apparent. This suggests that virus effect on red edge reflectance is at least partially independent of nitrogen-induced chlorophyll variation, potentially allowing early detection of infection under conditions of adequate nutrition.

A second study investigated the accuracy of real-time nutrient assessment technology through comparative analysis using visual assessment, the Leaf Evaluated-Nutrient System (Picketa LENS system; 2024 Corn Model), and conventional laboratory tissue sampling methods. For nutrient assessment, each method provided unique insights into plant nitrogen status but also revealed some limitations. Visual assessment effectively identified severe nitrogen deficiency through characteristic leaf firing symptoms. The Picketa LENS system showed similar overall trends in nutrient concentration measurement compared with the conventional laboratory method. The advantage of Picketa rests in the capability of immediate assessment of nutrient status; however, continued development and validation will be required.

Advisors: Gary Hein and Jeffrey Bradshaw

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