Fire Blight Control



Fire blight, caused by the bacterium Erwinia amylovora, is a common and frequently destructive disease of pome fruit trees and related plants. Native to North America, The disease enters the tree at the tips of the branches and then travels down the stems, causing dieback and can destroy limbs or in extreme cases even entire shrubs or trees.
HOST PLANTS: Common in pears but also appears in apples, loquat, crabapples, quinces, hawthorn, cotoneaster, pyracantha, raspberry and some other rosaceous plants are also vulnerable.

SYMPTOMS: In spring, branch and trunk canker symptoms can appear as soon as trees begin active growth. The first sign is a watery, light tan bacterial ooze that exudes from cankers (small to large areas of dead bark that the pathogen killed during previous seasons) on branches, twigs, or trunks. The ooze turns dark after exposure to air, leaving streaks on branches or trunks. However, most cankers are small and inconspicuous; thus infections might not be noticed until later in spring when flowers, shoots, and/or young fruit shrivel and blacken. The amount of fruit loss depends upon the extent and severity of the disease.

Open flowers are the most common infection sites and remain susceptible until petal fall. Infected flowers and flower stems wilt and turn black on pear trees and brown on apple trees. Fire blight infections might be localized, affecting only the flowers or flower clusters, or they might extend into the twigs and branches, causing small shoots to wilt and form a crook at the end of each infected shoot.  Succulent tissues of shoots and water sprouts (root suckers) also are subject to infection. Dead, blackened leaves and fruit cling to branches throughout the season, giving the tree a scorched appearance, hence the name “fire blight.” Infections can extend into scaffold limbs, trunks, or root systems and can kill highly susceptible hosts. Less susceptible varieties might be severely disfigured. Once infected, the plant will harbor the pathogen indefinitely.

When the pathogen spreads from blossoms into wood, the newly infected wood underneath the bark has pink to orange-red streaks. The bacteria also spread into the wood surrounding overwintered cankers that have become active in spring. If the bark is cut away from the edge of an active canker, reddish flecking can be seen in the wood adjacent to the canker margin. This flecking represents new infections the bacteria cause as they invade healthy wood. As the canker expands, the infected wood dies, turns brown, and dries out; areas of dead tissue become sunken, and cracks often develop in the bark at the edges of the canker. The pathogen tends to move in trees from the infection site toward the roots. In fall, leaves on infected pear shoots often turn red and then black.

FAVORED ENVIRONMENT: The fire blight bacteria overwinters in infected bark and is spread by splashing rain, dew, wind and insects. It spreads rapidly in moist, warm weather, especially during bloom.

FIRE BLIGHT CONTROL: Copper products are the only materials available to homeowners for fire blight control, and they often don’t provide adequate control even with multiple applications. A very weak (about 0.5%) Bordeaux mixture or other copper product applied several times as blossoms open might reduce new infections but won’t eliminate all new infections or those already existing in wood. The spray must be applied to open blossoms; thus the number of applications needed depends on the length of the bloom period. Once blossoms begin to open, make the first application when the average temperature (average of the maximum and minimum temperatures for a 24-hour period) exceeds 60°F. Apply at four- to five-day intervals during periods of high humidity and until late bloom is over. For pear trees, this might mean five to 12 applications per season. Copper products also might cause russeting or scarring of the fruit surface. The risk of this damage begins during bloom and increases as fruits enlarge.

Products for Fire Blight Control