Branch cankers are often on the underside of the branch. Infection of large branches and/or the main trunk occurs through natural openings and wounds like hail damage or pruning cuts. Apple leaves and shoots turn a rusty-brown color, while infected pear leaves and shoots turn black. Dead branches often develop a characteristic shepherd’s-crook hook at the tip and look like they have been scorched by fire. Typically, leaves killed by fire blight remain attached to the twigs for long periods. Affected portions turn various shades of brown and die. Usually infected leaves are killed entirely, but occasionally only a portion will show infection. Infected flowers wilt, turn brown and die, but the bacteria continue to multiply and infect new tissues moving into underlying twigs or branches.Īside from killing flowers, fire blight attacks leaves, twigs, branches, the main trunk and fruits. Infection of blossoms frequently happens first, after insects bring the bacteria into the flowers. Heavy infections occur when soil moisture is high, bud and shoot growth is rapid, and rainy periods are prolonged. Moisture is necessary for the bacteria to survive and initiate infection, along with moderate temperatures of 60 to 75☏. The amount and length of cool, rainy spring weather greatly influences how much fire blight we see each year. Then the bacteria are dispersed to new hosts by wind, rain, and insects. In spring bacteria begin multiplying rapidly and ooze to the surface of previous year’s cankers through cracks or natural openings as a clear, milky or amber-colored liquid. It’s caused by the bacteria Erwinia amylovora, which lives from one season to the next in cankers (dead sections of bark killed by the disease) on infected twigs, branches, or the main trunk. It’s one of the most serious diseases of apple and pear, both fruiting types and ornamentals, but also affects quince, chokeberry, cotoneaster, crabapple, hawthorn, raspberry, rose and spirea. Pruning and sanitation are important control strategies, but improper cleaning of pruning equipment between cuts can easily spread the disease.įire blight is a common and destructive bacterial disease of plants in the rose family. As pruning begins, it's important to have a good skills at identifying fire blight symptoms and have a multi-pronged approach for control, especially in very susceptible trees. It will be time to start pruning fruit trees later this month.
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