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Fire blight crabapple tree9/12/2023 ![]() ![]() Pruning tools must be disinfected between cuts to reduce the spread of the bacterium on tools. Active infections must be removed at least 12 to 15 inches below the margin of visible infection because the bacterium moves inside the plant ahead of visible symptom development. Removing active infection sites as they appear is important in reducing secondary inoculum. An application of a copper bactericide at bud break helps to reduce additional inoculum, which may be produced in cankers missed during pruning. The primary inoculum is reduced by pruning overwintering cankers during the dormant season. ![]() This management program is designed to reduce losses associated with the disease by reducing the amount of inoculum in the area, reducing the susceptibility of the plants with horticultural practices, and preventing new infections during favorable periods. In areas where fire blight is established, use a three-pronged approach to disease management. Hot, dry weather (over 90☏) slows or stops disease development, but does not cure the disease. This reddening can help to distinguish fire blight cankers from freeze injury.Įnvironmental conditions favorable for fire blight are rainy or humid weather with daytime temperatures in the range of 75° to 85☏, especially when night temperatures stay above 55☏. When the bacterium is active, the inner tissue (under infected bark areas) is water-soaked with reddish streaks. Symptoms include sunken and discolored areas (cankers), cracks, and bark splitting or peeling. Symptoms on mature woody tissue are somewhat difficult to discern from other types of injury, such as those caused by low- or high-temperature injury. 2 Young, succulent shoots infected with fire blight often develop "Shepher's crook". 1 Fire blight causes affected plant part to appear scorched.įig. The infected tissue turns gray-green, and eventually black.įig. Young, succulent shoots infected with fire blight often develop a characteristic "shepherd's-crook" symptom-the bending of the shoot tip to approximately 180° (fig. Infected fruits may exude large amounts of bacterial ooze. Fruits infected following injury by hail or insects develop red, brown, or black lesions. Fruits infected later in development do not shrivel as much or become as discolored as immature fruits. When infected early, the fruits remain small, become discolored, shrivel, and remain attached to the tree. On fruit, the symptoms depend on the stage at which the fruit was infected. On apple, it is common for the affected blossoms to cling to the spurs. The necrotic (dead) blossoms may or may not remain attached to the tree. One of the earliest symptoms of the disease occurs on flowers and is "blossom blight." The blossoms appear discolored (water soaked, gray-green color progressing to black). Secondary infections on young shoots are common following injury caused by hail, wind-blown dust, or insects. Infected tissue turns brown to black, shrivels and droops, but remains attached to the tree. The infection moves from blossoms to young fruit and then to adjacent leaves. The bacterium enters the plant through blossoms, wounds, and natural openings (such as stomata, hydathodes, lenticels, and nectaries). In spring when the bacterium becomes active, wind-blown rain or insects spread it from oozing cankers to blossoms. During periods of high humidity, infected tissue may produce a characteristic ooze. Fire blight can infect blossoms, fruit, stems, leaves, and woody branches. The characteristic symptom of fire blight is that affected plant parts (most notably the branch terminals) appear to have been scorched by fire (fig 1). Other hosts include rose, quince, hawthorn, loquat, almond, apricot, plum, cherry, chokecherry, mountain ash, raspberry, blackberry, and strawberry. In New Mexico, the disease is most common on apple, pear, crabapple, pyracantha, photinia, and cotoneaster. Within this plant family, the bacterium infects at least 39 different genera. It affects only plants in the rose family (Rosaceae). In commercial orchards, spray with bactericide.įire blight, caused by the bacterium Erwinia amylovora, is one of the oldest known bacterial diseases of plants.Sign: Watery ooze produced from infected plant tissue. Key symptom: Branch tips turn black as if scorched by fire. Hosts: Plants in the rosaceae family, notably apple, pear, pyracantha, cotoneaster, and photinia. This publication is scheduled to be updated and reissued 2/04.Ĭausal agent: Erwinia amylovora, a bacterium. Goldberg, Extension Plant PathologistĬollege of Agricultural, Consumer and Environmental Sciences New Mexico State University. ![]()
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