Some bacterial species are major pathogens of trees. Establishment, growth and the quality of trees can be affected by these disease outbreaks. Infected trees exhibit extensive necrosis of phloem and cambium, which can ultimately lead to dieback. The endophytic localization of and ability of these pathogens to create a protective matrix render them poorly accessible to control agents. The present invention provides methods and apparatus for controlling or stopping bacterial infections in trees by heat-treatment comprising incubation of plants or plant parts at about 39 DEG C for a period not less than 48 hours.