Assessing disease stress and modeling yield losses in alfalfa

Abstract

This dissertation consists of six chapters. There are two sections in the first chapter; the first section is a general introduction where the research problems and objectives are discussed. The second section is an extensive literature review where previous research concerning alfalfa diseases, disease assessment methods, and remote sensing methods are presented. Chapters 2 through 5 are in the form of journal papers. The second chapter addresses the effects of environmental factors (incident radiation, sun angle, leaf wetness, and sensor height) on remote sensing assessments. This new quantitative information was used to recommend a new assessment protocol that should improve the accuracy and the precision of remote sensing assessments. The third chapter quantifies and compares the inter-rater reliabilities and intra-rater repeatabilities of visual disease versus remote sensing assessment methods. The fourth chapter presents a comparison or single point and area under the curve (AUC) yield models using visual disease or remote sensing assessments as the independent variable. The fifth chapter quantifies the relationships between percentage defoliation, dry weight, percentage reflectance, and green leaf area index. The sixth chapter summarizes and discusses the implications of the research results achieved in this project. Literature Review Alfalfa diseases and yield losses Alfalfa diseases. Fungi, bacteria, nematodes, viruses, and phytoplasmas can all cause disease in alfalfa. Alfalfa pathogens and the diseases they cause are summarized by '' LAI = leaf area index. Asterisk indicates slopes are statistically different from zero at the P < 0.01 level. Day of Application Percentage Disease Disease Location Year vear Funeicide frequency defoliation incidence severity-I99S 113 Mancozcb Twice 41.56 ab 98.16 a I7.4S a 113 Propiconazolc Twice 39.89 ab 97.66 a 15.80 ab 113 Cupric Hydroxide Twice 39.51 ab 97.78 a 16.08 ab 113 Chlorothalonil Twice 37.35 b 97.59 a 16.43 ab 113 Mancozeb Once 36.34 b 98.32 a 16.66 a 113 Propiconazolc Once 41.02 ab 97.46 a 13.66 ab 113 Cupric Hydroxide Once 37.64 b 96.44 a 15.36 ab 113 Chlorothalonil Once 42.10 ab 98.52 a 13.85 ab 113 CGA-245704 Twice 40.22 ab 97.90 a 17.30 a 113 Non-treated control None 45.57 a 98.24 a 11.53 b