However, at warmer temperatures in the range of 70 to 80 F, especially with high humidity, bacterial populations explode, and soon reach levels that can cause blight. Below 60 F there is little bacterial growth, and low populations of bacteria don't present a fire blight risk. Their growth on and in plants is driven primarily by temperature. The bacteria are also present on non-symptomatic plant surfaces. amylovora can move systemically in plants, without producing symptoms. More bacterial ooze on these shoots, inoculum that can cause new infections as long as shoots keep growing.Į. Blossoms wilt and die within one to two weeks of infection, producing bacterial ooze that can infect new shoots. Insects and rain move bacteria to shoots, and they infect through microscopic wounds caused by wind-whipping or possibly insect feeding, or large wounds caused by hail. Insects deposit bacteria on stigmas in flowers, where they can multiply but typically do not cause infection unless washed to the nectary openings at the base of the flower by rain or heavy dew. Insects play a critical role in flower infection, when apples are most likely to become infected with fire blight. From there, they can be carried to other plants by wind-driven rain or insects. With warm weather, around 65 F, the bacteria multiply and come to the canker surface as sticky ooze droplets. The bacteria overwinter in bark and wood at the edges of cankers formed in previous growing seasons. All of these plants may be a source of inoculum. amylovora infects many plants in addition to apples and pears, including hawthorn, quince, mountain ash and cotoneaster. Alternatively, rootstocks may be more directly infected if root suckers are present and develop blight. The pathogen may not cause visible damage to the scion before traveling to the rootstock, where senstive rootstocks will rapidly collapse, killing the tree. Rootstocks may be more susceptible to fire blight than scions. Nearby shoots can be infected, producing a symptom called canker blight, where shoots have a characteristic yellow-orange color in the wilting tips in the early weeks after petal fall. As weather warms in the spring, the margins around cankers become less defined as bacteria move into surrounding tissue. Once in the main trunk of smaller young trees, the whole tree may rapidly wilt, turning brown or black, as if scorched.įire blight cankers are a site where E. Shoot blight can expand into older wood, causing dark, sunken cankers. Again, if the weather is warm and humid, bacterial ooze droplets may form at the base of the shoot. This wilting and browning or blackening of young, vegetative shoots is a classic fire blight symptom, with the young shoot tips bending over into a hook, like the curved end of a cane. One or more weeks after petal fall, shoot blight can develop. After wilting, the tissue may show a sticky white to yellowish ooze produced by the bacteria. Temperature drives symptom development. The warmer the temperature, the sooner symptoms appear and the faster infections spread. Bacteria may spread quickly, first wilting the entire blossom cluster which then turns brown or black, then spreading to adjacent leaves and shoots. Applications of Apogee or Kudos for shoot blight may be made during active shoot growth.įire blight symptoms can show on blossoms, fruit, leaves, shoots, branches and limbs, and rootstocks, and generally are readily recognized.īlossoms are often the first tissue to show fire blight symptoms. Infected flowers first have a water-soaked appearance that quickly turns black or brown. Chemical control begins with a copper spray at silver tip to green tip. Monitor weather data and use a forecast model to determine the need for antibiotics and biopesticides at bloom.Sanitation is accomplished by removing blighted shoots and whole trees.Fire bight management is a combination of tactics applied every year.Bacteria then migrate through the vascular tissue to the growing shoots and rootstocks killing tissue and whole trees. Infection of blossoms occurs during warm weather in conjunction with wetting events.Outbreaks in New England are sporadic, but have become more common in recent years. Fire bight is caused by the bacterium Erwinia amylovora.
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