![]() ![]() Disinfest tools regularly using bleach or ethanol. However, scouting and pruning must occur regularly to ensure the pathogen does not become well established in the canopy. Pruning out blighted stems and branches, at least 8–10″ away from symptomatic tissue (if possible), can effectively manage the disease in the landscape. Canopy dieback without a blackening of these tissues is unlikely to be caused by fire blight. The blackened appearance of infected plant parts will be uniform on leaves, petioles and stems. Proper identification is critical to managing fire blight. Noticeable blight symptoms arise approximately one to three weeks after infection, with symptoms appearing more rapidly during prolonged periods of wet and warm weather. Trees are most susceptible to infection when they are in bloom, with susceptibility dramatically decreasing before and after the bloom period. amylovora is often dispersed by splashing rain, wind and pollinating insects. ![]() Warm and wet weather facilitates pathogen development in the spring and E. The bacterium overwinters in diseased tissue, mostly at the edges of branch and stem cankers. Once plant parts are killed, they are typically colonized by other opportunistic cankering pathogens, making pathogen identification complicated as the growing season develops. However, bacterial ooze is often not visible or present in the field at the time of observation. The bacterial ooze is generally cream- to orange-colored and may extrude from branch/trunk cankers and lenticels or from young shoots. Signs of infection include oozing cankers and mummified fruits. Leaves, petioles, fruit and stems infected by Erwinia have a distinctly blackened appearance, which is why the disease is known as fire blight (blackened by fire). Infected shoot tips often curl, a symptom known as a "shepherd's crook". As the disease progresses, older stems and branches can become infected and die. The disease typically first appears as a blossom blight after wet and mild weather in May, but quickly spreads to infect fruit and current year's shoots and foliage. Cotoneaster, Crataegus and Sorbus), the disease is uncommon outside of apple and pear. While many other rosaceous plants can serve as hosts (e.g. Hostsįire blight is most common and severe on apple/crabapple ( Malus) and pear ( Pyrus). Use the search phrase “Streptomycin fire blight”.The bacterium Erwinia amylovora causes fire blight. Your best source is to look for suppliers on the Internet. Note: Streptomycin is rarely carried by garden centers. But when we have a long, mild spring, fire blight can be devastatingly obvious in many landscapes. Some years, fire blight is a minor problem. The ornamental ‘Bradford’ pear is somewhat resistant but other ornamental pears like ‘Aristocrat’ and ‘Capital’ are very susceptible. ‘Red Delicious’ apple and ‘Orient’ pear are resistant. ‘Bartlett’ pear, ‘Rome Beauty’ apple and ‘MacIntosh’ apple have no resistance to the disease and should not be planted by a homeowner. ![]() RESISTANT TREES Before planting an apple, crabapple or pear choose a variety resistant to fire blight. Collect all pruned branches and remove them from the premises. Submerge the pruner for five seconds after you make a cut. ![]() Make a solution of 1 part alcohol or chlorine bleach to 4 parts water and pour it into a shallow pan, such as a loaf pan. STERILIZE PRUNING SHEARS Your pruner may carry fire blight bacteria from wound to wound unless you sterilize it after each cut. The canker that oozes the harmful bacteria will be at the base of a dead twig, so make your pruning cuts 4-6 inches back from the black leaves into healthy wood on the branch. PRUNE BRANCHES Once you see the black leaves, pruning out and destroying the infected branches is the best course of action. Copper fungicides (click for sources) are bactericidal but they might cause russeting (freckles) on the fruit. Most f ungicides will not control this disease. SPRAY You can spray a bactericide like streptomycin (click for sources) during and after bloom to control the disease before it worsens. It is spread mainly by bees and flies that visit infected flowers when the tree is blooming and then take the disease to other parts of the tree. If many branches on a pear tree are infected, they may all turn black, like the tree was burned, leading to the name “fire blight”. The dead sprouts may be scattered on the tree or may only occur on one side. The most noticeable symptom is the sudden death of the new leaves at the end of a branch. Apples, crabapples and pears are susceptible in spring to a bacterial disease known as fire blight (fireblight). ![]()
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