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82 POTATO GROWER | JANUARY 2017 Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In DISEASE CONTROL | By Dennis A. Johnson & Thomas F. Cummings Washington State University Canopy environment is a factor for late blight management Friendly Environment The Columbia Basin of Washington and Oregon is similar to other regions of the world where potato late blight, caused by Phytophthora infestans, is dependent on the physical environment for development. Foliage and tubers of potato cultivars grown in the region are susceptible to infection, and aggressive genotypes of P. infestans are often present. Once initial inoculum of P. infestans is present, only a favorable environment and sufficient time are needed for epidemic development. The effect microenvironments within potato canopies have on late blight development has not been fully understood and needs to be better characterized to more efficiently manage the disease. Quantitative information for temperature and relative humidity in potato canopies is needed to augment decision support and disease forecasting systems. The purpose of a study conducted by Washington State University researchers was to quantitatively characterize canopy environment and estimate its potential Even in semiarid regions, a potato canopy's microenvironment can be highly conducive to P. infestans inoculation after row closure.