William E. MacHardy is a native of Maine. He obtained his B.S. and M.Ed. degrees in 1958 and 1965, respectively, from the University of Maine, his M.S. degree in biology from the University of Nebraska at Omaha in 1966, and his Ph.D. degree in plant pathology from the University of Rhode Island in 1970, where he worked with both Frank Howard and Carl Beckman. He joined the faculty of the University of New Hampshire (UNH) in 1972, was promoted to associate professor in 1977 and to professor in 1985, and was appointed professor emeritus in August 2001.
MacHardy was already an accomplished and respected researcher on water relations in vascular wilt diseases when he arrived at UNH. He was known for his keen perception of knowledge gaps that impeded progress in research and its application; a theme to which he often returned throughout his career. The reviews, book chapters, and papers he authored with Carl Beckman and Robert Hall are still relied upon in teaching and research. In 1978, he refocused his research on the epidemiology and management of apple scab, the most destructive disease of apples worldwide, and it is for this that he is perhaps best known today.
Commercially relevant control of scab had always required intensive spraying to prevent infection by ascospores, which overwinter in pseudothecia on fallen infected leaves. Intensive spraying continued until it was assumed that the ascospore supply was exhausted. However, no accurate, practical method existed by which this event could be forecasted over a large geographic area. MacHardy directed a series of studies that relentlessly generated the knowledge base to fill this gap. An improved method was developed to assess the maturity and discharge of ascospores (Phytopathology 72:92-95). The method was adopted by IPM programs in the United States and elsewhere and was continually improved (Plant Dis. 76:277-282 and 76:717-720). A model developed to estimate ascospore maturity based upon degree-day accumulation was validated by additional field studies (Phytopathology 72:901-904). The model was linked to weather forecasts to produce a true forecasting model to predict inoculum maturity up to 1 month in advance (Phytopathology 75:381-385). This simple, user-friendly model has been repeatedly validated, refined, and adapted (Plant Dis. 88:869-874); it has been translated and described in French, Italian, German, Spanish, and Portuguese; and variants exist within nearly every apple IPM program worldwide.
The Mills Infection Period Table for apple scab was a widely used but flawed method of identifying conditions for infection. Many had tried to either validate or refine its predictions with varied results. MacHardy initiated a 4-year orchard study in which he demonstrated that ascospore release by Venturia inaequalis was suppressed during nighttime hours (Phytopathology 76:985-990). Unknown to Mills, this caused daytime infection times to be substantially overestimated, i.e., infection occurred in less time than was specified in the Mills Table. MacHardy’s results were subsequently validated in several laboratory and field studies in the United States and Europe. His revised infection period table is now used worldwide and has more closely aligned the use of fungicides to the risk of infection.
The above work dealt with relative inoculum levels, i.e., that proportion of a pathogen population that was mature or had been discharged. However, decisions based upon relative inoculum potential presuppose the existence of a pathogen population sufficiently dense to cause significant disease in the absence of control. The relationship between absolute inoculum potential, or inoculum dose, and disease development had never been comprehensively investigated for apple scab. MacHardy recognized the impact of this gap in our knowledge (Prot. Ecol. 5:103-125) and directed studies that ultimately were among the first to apply Van der Plank’s equations for the practical timing of fungicide sprays. A system to forecast inoculum dose in commercial orchards used measurements of disease incidence and leaf litter (Phytopathology 76:112-118). From these simple measurements, an accurate forecast of inoculum dose was generated and used to determine how long the fungicide spray program could be delayed the following spring. The increased flexibility that this created in fungicide schedules allowed them to be integrated with insect and mite sprays. This work stands as an excellent example of the integration of disease and insect management programs for multiple pest systems (Plant Dis. 73:98-105 and 77:372-375). It furthermore served as the basis for MacHardy’s present work in orchard sanitation (Plant Dis. 84:1319-1326) as a means to augment control of apple scab. Long considered an intractable and classic “compound interest” disease, sanitation was widely regarded as an inefficient and impractical tactic against scab. MacHardy’s pragmatic combination of a seemingly outdated tactic of leaf litter removal with some otherwise arcane mathematics produced a workable and valuable solution to address the problem of eroding fungicide performance in commercial orchards. The simplicity and elegance of his solutions to such problems often belies the intense study and hard work involved in their creation.
MacHardy devoted nearly 10 years of his career to writing his book Apple Scab: Biology, Epidemiology, and Management for APS PRESS. With typical thoroughness and dedication, he collected and critically reviewed the thousands of journal papers, experiment station reports, and extension bulletins published on apple scab during the last century and synthesized new and valuable concepts and applications in the process. He traveled worldwide to personally interview authors and to have each chapter of the book reviewed by leading scientists in their respective areas of expertise. His book is recognized as the single most comprehensive treatment ever published by The American Phytopathological Society on a major plant disease.
MacHardy’s students and colleagues know him as a dedicated and talented mentor. He has served his society as editor, officer, and author and has greatly added to our knowledge of apple scab and its management. Researchers, IPM programs, and growers worldwide have benefited from this work, a fact acknowledged by his peers in 1996 when he was presented with the Award of Merit, the highest honor bestowed by the Northeastern Division of APS. For his many and valuable contributions, he is a particularly deserving nominee for fellow of The American Phytopathological Society.
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