David M. Gadoury’s research has had an immense impact on the management of fruit diseases over the past 25 years and his studies have profoundly influenced integrated pest management (IPM) practices on apples and grapes worldwide. Much of his research has focused on two of the most devastating and extensively studied diseases of fruit crops: apple scab and grape powdery mildew. In each case, his findings have substantially revised long-held views. A major goal of his research has been to clarify how pathogens survive the intercrop period and then become reestablished in the crop. Gadoury thus chose a less-traveled path, since many labs study disease increase but few investigate what sets the stage for an epidemic.
His impact on the epidemiology and management of apple scab has been profound. Prior to his work, there was no practical way to relate inoculum dose to disease management practices. As an M.S. and Ph.D. student with William MacHardy at the University of New Hampshire, and later at Cornell University, Gadoury pioneered the potential ascospore dose (PAD) concept and conducted the field and lab studies to define an action threshold that growers could use to time initiation of a springtime fungicide spray program. This action threshold improved the efficiency of fungicide spraying and provided David M. Gadoury growers with a way to integrate sanitation practices for overwintering leaves in order to minimize fungicide needs. The PAD action threshold and the model to estimate ascospore maturity have since been incorporated into apple scab IPM programs worldwide.
Gadoury’s contribution to scab epidemiology extends well beyond the PAD concept, however. His collaborative studies with colleagues in the United States and Norway included (i) impact of the environment (dew, light, and relative humidity) on the discharge and dissemination of ascospores, which led to a major revision of the traditional Mills Table for assessing scab risk; (ii) elucidation of the influence of temperature on the development of pseudothecia, asci, and ascospores, culminating in a degree-day model supplementing the PAD approach; (iii) preparation and interpretation of pseudothecial assessment methods to trace ascospore maturation and release; and (iv) clarification of variation and reduction of sources of error in squash mounts. Few scientists have had a more diverse and far-reaching impact on the study and management of apple scab.
Gadoury’s collaboration with Roger Pearson at Cornell overturned a century of dogma concerning the role of cleistothecia in grape powdery mildew. Cleistothecia were previously believed to be degenerate structures that were nonfunctional because few viable structures were found on leaves and inoculum from these structures failed to reproduce the disease. Gadoury and Pearson discovered that the cleistothecia were passively dispersed by late-summer rains from the site of formation on leaves to crevices within the bark of the vine. This insight forced a complete reassessment of the role of cleistothecia in the disease cycle and explained why disease management programs that focused on other putative sources of inoculum often provided mediocre control. The model of passive dispersal of cleistothecia to secondary substrates has since been demonstrated in several other pathosystems. Gadoury and Pearson received the Lee M. Hutchins Award of APS in recognition of this innovative work.
Equally important was Gadoury’s role with others at Cornell in establishing the critical function of early-season control of grape powdery mildew. In a series of elegant lab and vineyard studies lead by Gadoury, they showed convincingly that ontogenic resistance limits susceptibility of grape berries to a 4-week period around bloom, disproving the long-held view that berries remained susceptible for 2 months. The outcome of this breakthrough was a significant adjustment and reduction of fungicide spray schedules worldwide. By precisely identifying the end of the susceptibility period, Gadoury and colleagues also helped wine-grape growers avoid premature termination of spraying that contributed to an insidious form of the disease called “diffuse powdery mildew,” which predisposes grapes to contamination by spoilage microorganisms that create off-flavors in wine.
The impact of Gadoury’s work in fruit pathology is affirmed by 66 refereed research publications, nearly 800 citations of his papers (an extraordinary number in fruit pathology), numerous visiting research and lecture experiences around the world, and service on review panels. Comments by colleagues on his impact were uniformly glowing. A prominent colleague states that “he is THE authority worldwide on apple scab and grape powdery mildew.” Colleagues consistently stated that “his papers should be required reading for all grad students in plant pathology…because of their logical and systematic approach and painstaking attention to detail.” Gadoury was also praised for “the amazing breadth of his approach to solving problems, ranging from mycology to epidemiology, genetics, biophysics, and molecular host-pathogen interactions.”
Gadoury is an enthusiastic and committed citizen of his department and of APS. He is seen as a “brilliant mentor for graduate students” whose “natural and infectious curiosity challenges his students” and has created a “legacy of students with successful careers in plant pathology.” He has lectured internationally on writing effectively for diverse competitive grants programs and on the process of preparing articles for refereed journals. He has advocated forcefully and effectively, both at Cornell and through APS committees, for a greater emphasis on undergraduate teaching and work experience in order to recruit future plant pathologists, and he now chairs a committee tasked with identifying future challenges to the profession of plant pathology.
For his innovative contributions to fruit epidemiology, highly effective mentoring of young scientists, and exemplary service, Gadoury is truly worthy of receiving the APS Fellow Award.
A native of Rhode Island, Gadoury received his B.S. degree from the University of Rhode Island in 1978. His M.S. and Ph.D. degrees in plant pathology were earned at University of New Hampshire in 1981 and 1984, respectively. At the New York State Experiment Station in Geneva, he was hired in 1985 as a research associate II, rising to research associate III in 1990 and to senior research associate in 1993. Gadoury is an avid hiker and skier and is completing a second round of ascents of all 48 high peaks in the White Mountains of New Hampshire.
