The worst epidemics always follow blossom infection. Secondary infections may continue to occur throughout the growing season. Infected shoots provide additional sources of fire blight bacteria, which can be spread by rain, (especially wind-blown rain), insects, and contaminated pruning tools. Blossom infections become visible as "strikes", or dying shoots in anywhere from 1 to 4 weeks, depending on the temperature. Once blossoms are infected, the bacteria can quickly spread into shoots and branches. This gives fire blight explosive potential if the conditions for blossom infection are met. Bacteria can then be spread very efficiently from blossom to blossom by honey bees. If weather conditions are warm and humid, the bacteria are able to multiply rapidly in the blossom nectar. This ooze, consisting of millions of bacterial cells, is easily transported to blossoms by insects such as flies, ants, and beetles. During spring and early summer, cankers that were not removed the previous season may reactivate and produce bacterial ooze, which may or may not be visible. Leaf discolouration in late summer caused by fire blight rootstock blightįire blight bacteria overwinter primarily in cankers on infected trees. Oozing bark may be observed near the base of the tree.įire blight rootstock blight. Trees may weaken and die beginning one to several months after planting. It is sometimes mistaken for crown rot due to brown discoloured tissue under the bark at the base of the tree. Rootstock blight may not exhibit typical fire blight symptoms. Cankers may also expand to girdle limbs.įire blight may also spread into the root area, leading to tree death. Invaded shoots wilt and die, and may be mistaken for early shoot blight. Bacteria that overwintered in holdover cankers begin to multiply and invade nearby shoots or water sprouts. Shoot blight caused by reactivating cankers in the spring is known as canker blight. Later in the season the bark often cracks around the margins of the canker. Reddish brown streaks may be seen in the cambium under the bark of diseased branches. Pear orchard heavily damaged by fire blightĬankers appear as slightly darker, water soaked areas in the wood, which may produce amber coloured bacterial ooze that runs down the bark. Note browning of leaves and shepherd's crook and at end of shoot.ĭroplets of amber coloured bacterial ooze on fire blight-affected pear shootįire blight-infected apple fruitlet, with bacterial ooze Note blackening of pedicels (flower stems) In susceptible hosts or young trees the disease may travel rapidly down branches causing girdling and death of the branches or sometimes the main trunk.īlossom blight on pear. When shoots attached to scaffold limbs or trunks are attacked, the pathogen may spread into the structural wood causing cankers. Blighted leaves may remain attached to the tree throughout the winter. During warm and humid or rainy weather drops of milky to amber coloured bacterial ooze frequently appear on the blighted shoots and fruit. Infected shoots (or "strikes") wilt rapidly, and often form a shepherd's crook at their tips. Fruitlets quickly turn brown to black and eventually shrivel up.īlighted pear shoots are black in colour, while infected apple shoots are usually a lighter shade of brown. Young fruitlets are also very susceptible and appear water soaked and slightly off-colour soon after infection. Blighted blossoms appear wilted, shriveled and brown. Treat for sucking insects such as aphids, leafhoppers, plant bugs, and pear psyllid that wound tissue, permitting entry of bacteria.Fire blight symptoms may appear on the blossoms, shoots, branches, trunk and rootstock.Apply slow-release fertilizers in early spring or late fall after growth has ceased.Do not toss clippings around as this spreads the bacteria. During the growing season, place pruned material in a container and cover it before leaving the area. Remove infected wood several inches below cankers during the dormant season, if applicable.Bacteria ooze from the blossoms and fruit during wet, humid weather.Small, slightly sunken, and brown cankers (Older cankers are dark brown and sunken with brown tissue under the bark.).Wilt and blackening of leaves and twigs which form a “Shepherd’s crook”.The pathogen travels down into the shoots and into fruit spurs. In the spring, during wet weather, the bacteria is splashed onto blossoms by rain or pollinating bees. Hosts:Ĭrabapple, apple, cotoneaster, firethorn, hawthorn, mountainash, pear, and quince are plants most commonly damaged. Under the right conditions, it can destroy an entire orchard in a single growing season. It is a serious concern to apple and pear producers. Fire Blight is a bacterial disease affecting apples, pears, and some other members of the family Rosaceae.
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