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The three-season evolution of a fire blight outbreak in a nursery using an asymptomatic apple bud wood source contaminated with Erwinia amylovora

Smith, T.J.
Acta horticulturae 2002 no.590 pp. 109-113
Erwinia amylovora, apples, cross contamination, cultivars, growing season, nursery stock, orchards, planting, rootstocks, trees, wood
A serious outbreak of fire blight occurred in a large nursery planting of apples on various rootstocks in Fall 1999, three weeks after budding of the rootstocks. Fire blight symptoms were visible on a high percentage of a specific apple cultivar. Apple rootstock trees budded prior to the affected cultivar were symptomless. Apple rootstock trees budded to other cultivars on the same day, but after the affected cultivar, also showed symptoms, but to a much lesser degree. Despite careful and frequent removal of all plants showing fire blight symptoms, individual nursery trees continued to develop the disease throughout the 2000 growing season, and after transplanting into commercial orchards in Spring 2001. A total of 47100 trees was lost in the nursery due to this infestation. The probable initial infection process involved infected but asymptomatic bud wood source trees and cross contamination of previously non-contaminated bud wood during bud wood collection, storage and budding. Efforts to eliminate the infected nursery stock by removal of symptomatic nursery trees were highly, but not entirely successful. Symptoms of the disease are described on the rootstock plant (liner), the apple cultivar nursery tree, and the first three months after commercial planting. A management plan for the reduction of fire blight damage in the affected nursery has circumvented similar fire blight outbreaks in the 2000 and 2001 growing seasons.