Language English Fire blight on crabapple Photo: Jardin botanique de Montréal (Pascale Maynard) Fire blight - Sorbus. Photo: Jardin botanique de Montréal (Pascale Maynard) OngletsDescriptionSummaryThis bacterial disease, which frequently strikes various species in the Rosaceae family, progresses very quickly and can be fatal. An infection spreads like wildfire, particularly during warm, damp and rainy springs. Damaged tissue appears scorched: flowers and young shoots suddenly wilt, dry up and turn black, but remain attached to the plant. The bark on infected branches turns reddish brown, making it easy to distinguish from healthy wood. Young trees are more vulnerable and can be killed in just a few weeks. Mature trees may lose a few branches and either recover or succumb within one or two growing seasons. Signs and symptomsThe first signs of damage generally appear in spring, shortly after blooming. The flowers appear water-logged, then shrivel and quickly turn black. The damage spreads rapidly to new shoots, which shrivel in turn and bend in a shepherd's crook. Infected fruit turns dark and hardens. The infected parts often remain clinging to the plant. The dried flowers and leaves are leather-like. The disease moves through conductive vessels to secondary branches and main branches, eventually reaching the trunk. The collar and rootstock may also be affected. The bark on newly infected branches swells and lifts; under the bark, the tissues become dark, damp and shiny. Later, the bark becomes dry and cracks; the infected portion of the branch turns reddish brown, making it easy to distinguish from healthy wood. Amber-coloured sticky liquid flows from all the infected parts; this sweet liquid, which is full of bacteria, attracts insects that disperse the infection throughout the summer. In late summer, sunken cankers appear on the branches and trunk; plant parts above the cankers die back. The disease can be fatal to young trees in just a few weeks. Mature trees may lose a few branches and either recover or succumb within one or two growing seasons. Latin name (genus)Erwinia amylovoraHost plantsVarious species of ornamental and fruit plants and trees in the Rosaceae family, including apple, burning bush, cherry, chokeberry, cinquefoil, cotoneaster, crabapple, false spirea, hawthorn, kerria, mountain ash, ninebark, pear, quince, plum, raspberry, rose, serviceberry and spirea. Name of host plants Development cycleDescription and life cycleErwinia bacteria are flagellated and rod-shaped. They are capable of surviving and thriving with or without oxygen. These micro-organisms overwinter on infected plants, on the margins of cankers formed in the previous year and possibly in buds and branches over 1 cm in diameter. The following spring, during warm, humid spells, the bacteria become active and multiply very rapidly: cell division may occur every thirty minutes. Masses of bacteria form, swelling tissues under the bark, which cracks and oozes a sticky liquid containing sap and bacteria. This sweet ooze attracts insects, which transfer the bacteria to other plants or other parts of the same plant. The bacteria enter plants through flowers, wounds and even the smallest openings in plant tissue. Once inside, they move through the vascular system, rapidly blocking vessels and causing young shoots to wilt in the characteristic shepherd's crook. During the growing system, the bacteria can also be spread by wind, rain, watering and handling by gardeners. In late summer, the bacteria gradually become inactive and remain dormant until the following spring. Prevention and controlFavourable conditionsThese bacteria multiply in damp, rainy weather at temperatures of 18 to 25°C, particularly at blooming time and when the young shoots are growing and sap is flowing abundantly. The risk of infection is higher when there are diseased wild plants in the Rosaceae family nearby. Heavy feeding with high-nitrogen fertilizer and drastic or late-season pruning predispose plants to the infection. IdentificationIn early spring, before leafing, inspect branches for any discoloured bark. At blooming time, inspect flowers and young shoots, because that is when the disease spreads fastest. Continue your inspections until mid-summer. PreventionChoose species or cultivars that are resistant to this disease, including: Crabapple: 'Cardinal', 'Coralburst', 'Dolgo', 'Flame', 'Harvest Gold, 'Lollipop', 'Maybride', 'Molten Lava', 'Morning Princess', 'Ormiston Roy', 'Pink Spires', 'Prairie Fire', 'Ralph Shay', 'Red Jewel', 'Royal Beauty', M. sargentii 'Tina', 'Sir Lancelot', 'White Angel' and 'Winter Gold'. Apple: 'Enterprise', 'Freedom', 'Liberty' and 'Williams Pride'. Pear: 'Golden Spice', 'Moonglow', 'Nova', 'Seckel', 'Summercrisp' and 'Ure'. Keep plants vigorous by fertilizing them adequately, pruning them properly and watering them during dry spells; never damage plants unnecessarily. Avoid planting in heavy, poorly drained soil; never water plants by spraying them and never prune in humid weather. Avoid heavy feeding with high-nitrogen fertilizer and drastic or late-season pruning, which predispose plants to the infection. Physical controlImmediately remove any infected branches; cut into healthy wood at least 30 to 50 cm (12 to 20 inches) below any visible discolouration on the bark; always prune in dry weather. Sterilize pruning tools between each cut with a 70% isopropyl (rubbing) alcohol solution. Rake up and destroy infected leaves and fruit; dispose of all infected parts that you remove and all plant litter. If the disease has affected main branches and the trunk, cut the tree down, being sure to remove all roots; dispose of all diseased plant parts. Biological controlNone available. Chemical controlThe Montréal Botanical Garden does not recommend the use of pesticides to control this disease.