Fire blight: A devastating disease of rosaceous plants
Fire blight is a bacterial disease that affects many plants in the rose family (Rosaceae), such as apples, pears, quinces, loquats, crabapples, hawthorns and roses. The disease is caused by the bacterium Erwinia amylovora, which can infect blossoms, shoots, branches, fruits and roots of susceptible plants. Fire blight can cause severe losses in orchards and ornamental plantings, especially in warm and humid weather conditions.
Symptoms and signs
The most characteristic symptom of fire blight is the wilting and browning of young leaves and shoots, which bend downward forming a hook-like shape. The infected tissues appear as if scorched by fire, hence the name of the disease. The infection can spread rapidly through the vascular system of the plant, causing dieback of branches and cankers on the bark. Cankers are dark brown to black lesions that may ooze a sticky liquid containing millions of bacteria. The ooze can be dispersed by insects, wind or rain to infect new plants or tissues. Infected fruits become water-soaked, shrivelled and brown or black.
Fire blight is difficult to control once it is established in a plant or an area. The best strategy is to prevent the introduction and spread of the disease by using resistant varieties, removing infected plants or plant parts, avoiding excessive fertilization and pruning, and applying protective sprays of copper or antibiotics before flowering. However, these measures may not be completely effective and may have negative impacts on the environment or human health. Therefore, more research is needed to develop new methods of fire blight management that are safe, sustainable and effective.
Fire blight | Description, Symptoms, & Treatment | Britannica
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Fire blight | UMN Extension
Causes and transmission
Fire blight is caused by the bacterium Erwinia amylovora, which belongs to the same group of bacteria that cause diseases in humans and animals, such as salmonella and E. coli. The bacterium can survive in plant debris, soil or water, but it needs a wound or a natural opening to enter the plant. The most common entry point is the flower stigma, where the bacterium can multiply and move down the style to the ovary and then to the rest of the plant. The bacterium can also enter through wounds caused by insects, hail, pruning or other mechanical damage.
The transmission of fire blight occurs mainly through the movement of the bacterial ooze that forms on infected tissues. The ooze can be carried by insects, especially bees that visit flowers, or by wind-blown rain that splashes the ooze onto nearby plants. The ooze can also contaminate tools, equipment, clothing or hands of people who handle infected plants. The bacterium can remain viable for several months on these surfaces and infect new plants when conditions are favorable.
Prevention and control
The prevention and control of fire blight depend on a combination of cultural, biological and chemical methods. Some of the most important practices are:
Using resistant or tolerant varieties of plants. Some cultivars of apples, pears and other rosaceous plants have been bred or selected for their ability to resist or tolerate fire blight infection.
Removing and destroying infected plants or plant parts as soon as possible. This reduces the source of inoculum and prevents further spread of the disease. Infected material should be burned, buried or disposed of in a sanitary landfill.
Avoiding excessive fertilization and pruning. These practices can stimulate the growth of succulent shoots that are more susceptible to fire blight infection. Pruning should be done in late winter or early spring when the risk of infection is low.
Applying protective sprays of copper or antibiotics before flowering. These chemicals can reduce the number of bacteria on the flower stigmas and prevent infection. However, they have to be applied at the right time and frequency, and they may have negative impacts on beneficial insects, human health or the environment.
Using biological control agents. These are natural enemies of fire blight bacteria, such as other bacteria, fungi or viruses that can compete with or inhibit them. Some examples are Pantoea agglomerans, Bacillus subtilis and Bacteriophage. These agents can be applied to flowers or wounds to prevent or reduce infection.