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Epidemiology and Management of Foliar Diseases in Asparagus (Asparagus officinalis L.)

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Title: Epidemiology and Management of Foliar Diseases in Asparagus (Asparagus officinalis L.)
Author: Foster, Jennifer Marie
Department: Department of Plant Agriculture
Program: Plant Agriculture
Advisor: McDonald, Mary Ruth
Abstract: Foliar diseases caused by Stemphylium vesicarium and Puccinia asparagi are an increasing problem in the major asparagus production regions of eastern and central Canada. Replicated and repeated controlled environment and field trials were conducted in Ontario to assess the disease reaction of host crops, compare fungicide efficacy and the Tom-Cast forecasting model, test fertilizer amendments and investigate the epidemiology of Pleospora herbarum (teleomorph of S. vesicarium) on asparagus fern. All of the lines of asparagus assessed were susceptible to infection by S. vesicarium, however, certain lines from the University of Guelph demonstrated quantitative resistance to rust (P. asparagi). Purple spot infection on spears was not consistently correlated with severity on ferns. Stemphylium vesicarium can cross-infect asparagus, but some host adaptation or specialization, possibly via host-specific toxins, appears likely. The pathogen was shown to colonize necrotic leaves of fall rye, which is often used as a cover crop in asparagus fields. Several fungicides demonstrated promising efficacy against rust, however, less control of S. vesicarium was observed. The forecasting model Tom-Cast had limited success in both low and high fertility programs. The results show that forecasting models need to be validated locally, in asparagus cultivars relevant to production today. The development of pseudothecia on fern was correlated with fern yellowing and chlorophyll concentration in outdoor trials, however, no pseudothecia developed in controlled environment studies. Greater understanding of the environmental factors that contribute to pseudothecia maturity would enable growers to better time management strategies. The presented study has contributed to the understanding of the etiology and epidemiology of S. vesicarium in asparagus, and also validated and tested new tools for control of foliar disease in asparagus. An integrated disease management strategy that includes cultivar selection, timely application of fungicides and inoculum management may reduce crop losses and asparagus decline.
Date: 2018-04
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