Severe cankers girdle and kill infected limbs. Bark covering the cankered area is sunken, rougher and separates from injured tissue. Cankers are at first water soaked, later brownish red, and ultimately dark brown or black. A tan-yellow bacterial exudate (ooze) often appears where infection occurs.Ĭankers develop on trunks, limbs, and the graft union. Infected blossoms frequently are distorted. They turn brown to black and rapidly wilt and die. Symptoms During moist periods in the bloom season, spurs, blossoms, and twigs may become infected, developing a darker, water-soaked appearance. In a "fire blight year," young trees, especially those trained to a central leader, can be severely damaged. It is not common in Oregon's Willamette Valley and may be confused there with Pseudomonas blight. Since the mid-1990s, the disease has become very important to apple growers because susceptible cultivars have been planted widely.
It is sporadic in Milton Freewater, Hood River, and Medford, OR and in Yakima and Wenatchee, WA. Fire blight may be very serious some years but appears hardly at all in others. Fire blight also severely attacks apple, cotoneaster, photinia, pyracantha, hawthorn, quince, and mountain ash. Although bees have been shown to be capable of transmission in controlled conditions, field-collected pollinating bees in New York did not test positive for the bacterium.Īll important pear cultivars are susceptible to fire blight, including Bosc. Bees do not feed on bacterial ooze but can visit infected flowers and spread bacteria to uninfected flowers. Flies and ants are attracted to the bacterial ooze and can then carry it to uninfected blossoms. Aphids, flies, ants, leafhoppers and tarnished plant bugs have been implicated in the spread of fire blight. Primary insect vectors include ants, flies, and wasps. Symptomless pears are not a source of the pathogen, which is rarely detected (1 out of 5,600 fruit) as an epiphyte on commercially-produced fruit. Entrance into healthy appearing leaves and shoots may be through the base of epidermal hairs. Vigorously growing shoot tips, young leaves, and wounds also can be infection sites. Flowers, which are open for up to 3 days, support rapid growth of the bacteria while older flowers do not.
#FIRE PEAR PLUS#
A temperature of 65☏ or higher in a 24-hour period plus a trace of rain or high humidity (greater than 65%) is necessary for infection. Bacteria enter healthy, main bloom or rattail blossoms through the stigma, nectary, anthers, and sepals. Insects, pruning tools, and splashing rains spread this bacterium. Risk of infection increases with the number of more active "holdover" cankers in an orchard. Cause Erwinia amylovora, a bacterium that overwinters in cankers on infected pear, apple, and some ornamental trees.
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