Fire blight of apple extension1/14/2024 The bacteria can colonize natural openings in the bark, such as lenticels, and areas where the bark has been wounded from pruning cuts, hail damage or mechanical damage or it can move systemically through the tissues of the plant from infected blossoms or shoots. ![]() Cankersįire blight cankers of various sizes can develop on twigs, limbs and even the trunks of trees. Spur infection of fire blight kills leaves and shoots. Tender shoots infected with fire blight have the typical "shepherd's crook" appearance. In either case, the dead leaves remain attached to the dried shoots. Apple leaves and shoots turn a rusty brown color in pears, these parts turn black (Figure 3). These infections often kill a foot or more of the terminal growth. When infected, the tender tips wilt, die and assume a characteristic shepherd’s-crook appearance (Figure 2). The succulent new shoot growth also is susceptible to bacterial infection in the spring and early summer. Infected blossoms turn brown and die, usually with the flower parts remaining attached. Bacteria multiply rapidly in the blossom nectar and infect the blossoms through natural openings called nectaries. This is partly because of their attractiveness to insects, which carry the bacteria from the cankers. The blossoms on susceptible trees are usually the first plant parts to become infected in the spring. ![]() Symptoms and plant parts attacked Blossom blight Careless pruning practices may also spread the bacteria. The bacteria are usually spread from the cankers by insects and by wind-blown rain. The bacteria commonly overwinter in cankers (sunken diseased areas) on the tree, which produce a sticky exudate in early spring (Figure 1). The arrow points to a fire blight canker on a large limb.įire blight is a bacterial disease affecting apple, crabapple, pear, hawthorn, pyracantha (firethorn) and related species.
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