Fire blight: what the extension services record

This page describes what the named sources say. It is not a diagnosis of any tree and does not say what should be done with one. None of the four pages read lists fire blight as regulated or notifiable. Each section names its source, all read on October 9, 2026. The full list of diseases is on the tree diseases page. Pruning of fruit trees is covered separately on the fruit tree pruning page.

Cause and hosts

All four sources name the cause as the bacterium Erwinia amylovora. NC State Extension says it has been reported in all major apple growing regions of the United States and can occur on more than 75 species of trees and shrubs. UC Statewide IPM calls it common and frequently destructive on pome fruit trees and related plants, and says pear and quince are extremely susceptible, with apple, crabapple and firethorn frequently damaged. It lists hawthorn, Spiraea, Cotoneaster, toyon, serviceberry, loquat and mountain ash as less commonly affected. The University of Wisconsin-Madison calls it the most destructive bacterial disease of plants in the rose family and adds rose to the host list. Clemson says some ornamental pears once thought resistant, such as Bradford, can be infected when conditions suit, and that the highly invasive callery pear along field edges is very susceptible and can be a source of the disease.

What the sources describe on the tree

Part of the tree	What is recorded	Source
Blossoms	Infected flowers wilt and turn black on pear and brown on apple. A blossom can look healthy through petal fall, with wilting one to two weeks after.	UC Statewide IPM; NC State Extension
New shoots	The tip bends into a shepherd's crook. Leaf midveins blacken, then the whole shoot wilts and turns black. Dead leaves and fruit cling to the branch.	NC State Extension; Clemson; UC Statewide IPM
Cankers on branches and trunk	Sunken, water-soaked then dark areas, sometimes with cracked bark, that emit a sticky or milky ooze. The bacteria survive in them.	Clemson; University of Wisconsin-Madison
Wood under the bark	Pink to orange-red streaks where infection moves from blossom into wood; reddish flecking at the edge of an active canker; reddish brown sapwood around cankers.	UC Statewide IPM; University of Wisconsin-Madison
Rootstock	A canker that can girdle and kill the tree. The above-ground rootstock turns black, leaves redden and wilt, usually seen in late summer or early fall.	NC State Extension
Fruit	Brown, sunken or shrivelled areas that can be sticky; young fruitlets blacken and are harder to pull off.	University of Wisconsin-Madison; NC State Extension

UC Statewide IPM says the dead, blackened leaves and fruit that cling through the season give a scorched look, which is the origin of the name. It adds that most cankers are small and inconspicuous, so infection may not be noticed until flowers, shoots or young fruit shrivel and blacken later in spring.

NC State Extension sorts the disease into four forms: blossom blight, shoot blight, rootstock blight and canker blight. UC Statewide IPM says that once infected, a plant harbours the pathogen indefinitely.

Life cycle

UC Statewide IPM, NC State Extension and the University of Wisconsin-Madison agree on the main pattern. The bacterium overwinters at the margins of cankers. When spring turns warm and moist, a small share of cankers become active and ooze. UC Statewide IPM gives the ideal conditions for infection as rainy or humid weather with daytime temperatures of 75 to 85 degrees Fahrenheit, especially when nights stay above 55. Clemson says first symptoms occur in early spring above 60 degrees when it is rainy or humid, and NC State Extension gives warm weather of about 65 degrees with rain for the rapid multiplication.

Splashing rain and insects carry the ooze to blossoms and soft shoots. UC Statewide IPM says honey bees become efficient carriers once blossoms are contaminated, and the University of Wisconsin-Madison says honeybees can feed on the ooze and carry the bacterium to flowers. NC State Extension names flies as the main early movers of ooze to open blossoms and says bacteria wash from the surface of the flower into its nectar openings during wetting such as rain or heavy dew. It names a second route to shoot blight: the youngest three to four leaves on a shoot, infected through insects with sucking or piercing mouthparts, or through wounds from wind-blown soil or hail.

UC Statewide IPM says the bacteria move in narrow paths in the outer bark, up to 1 1/2 inches wide, and can run 2 to 3 feet past the visible edge of a canker. It also says the pathogen tends to move toward the roots, that vigorous shoots are hit hardest, and that trees are more susceptible when young.

Confirmation and status

The University of Wisconsin-Madison clinic page says very few diseases can accurately be diagnosed by eye and describes a paid sample service. The directory lists the plant disease and insect diagnostic labs in the United States. None of the four pages names a quarantine, a notifiable status or a report line.

What the sources say about control

Clemson and the University of Wisconsin-Madison both say there is no cure. NC State Extension describes forecasting models, and UC Statewide IPM, NC State Extension and Clemson also describe resistant varieties and spray programmes for orchards and gardens. This page gives no product names, rates or timings.