Yield Loss Models for Foliar Diseases of Alfalfa and Evaluation of Chemical and Cultural Disease Control Methods
Broscious, Steven Charles
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Permalink
https://hdl.handle.net/2142/70606
Description
Title
Yield Loss Models for Foliar Diseases of Alfalfa and Evaluation of Chemical and Cultural Disease Control Methods
Author(s)
Broscious, Steven Charles
Issue Date
1986
Department of Study
Plant Pathology
Discipline
Plant Pathology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Plant Pathology
Abstract
Regression models relating various measures of disease level to yield were developed for the complex of fungi which cause foliar disease on alfalfa (Medicago sativa). The accuracy and precision of the models was evaluated using data other than those from which the models were constructed. Linear models using disease severity one week before harvest (DS1), on the day of harvest (DS0), or area-under-disease-progress curve (AUDPC) to predict yield as percent of maximum explained 52 to 60% of the variation in yield. Models estimated a yield reduction of 2.40, 1.83, and 0.142% for each DS1, DS0, and AUDPC unit, respectively. All models overestimated yield but were more accurate within the range of disease levels commonly observed in alfalfa fields than at higher levels. Field studies were done to determine the economically optimal fungicide application frequency and timing for control of alfalfa leaf spot diseases and identify the predominant fungal pathogens responsible for causing foliar disease. A single application of mancozeb after 10 to 14 days of regrowth was the most profitable treatment schedule with a 215% return on investment and net marginal return of $20.58/ha. Stemphylium botryosum and Phoma medicaginis were the predominant pathogens with Leptosphaerulina and Colletotrichum spp. also present at lower but significant levels. The contribution of an early harvest towards minimizing yield and quality losses due to foliar diseases of alfalfa was evaluated. High and low levels of disease were established using inoculations and fungicides. Fungicide protected plots yielded more dry matter, crude protein, and digestible dry matter. Differences between disease level treatments for these variables increased with time. However, even at high disease levels, values for these response variables increased over time. Hay digestibility was reduced when disease levels were high and decreased with time regardless of the disease level treatment. Therefore, early harvesting of alfalfa affected by foliar disease may improve hay quality but not the quantity of dry matter and quality constituents.
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