Bacterial ooze appears on the new infections soon after the symptoms, providing additional sources of bacteria for new infections. At 75☏, blossom blight and shoot blight will be evident in four to five days. Shoots become infected through natural wounds, such as broken leaf hairs.

Bacteria need this natural opening to enter the plant they cannot directly penetrate plant tissue. Infections occur when the bacteria are washed off from the stigmas and move down into the nectarthodes of the blossom. If the average temperature is 60☏ or above and relative humidity is 60 percent or more, or there is rain, new infections can occur. Insects also transmit bacteria to growing shoots. The bacteria reside on the flower stigma where they do not cause disease, but replicate to high numbers when temperatures are favorable. Blossom-to-blossom transmission is carried out mainly by bees and other insects that visit the flowers. The bacteria are spread to blossoms primarily by wind and rain with some transmission by pollinators. Once the temperature reaches about 65☏, bacteria begin to multiply and appear on the outsides of the cankers in drops of clear to amber-colored ooze. Disease cycleīacteria overwinter in the margins of cankers on branches and trunks. Later the fruit becomes leathery, turns brown (apples) and black (pears and quince), shrivels, and usually remains attached to the fruit spur. Droplets of bacterial ooze appear on the surface.

The bacteria may also invade fruit, which becomes water-soaked. This is also referred to as 'canker blight.' They will ultimately move from the cankered regions to growing tissue, thereby causing shoot blight. During the growing season, the bacteria continue to replicate and move through the vascular system. If previous season cankers remain in the tree, shoot blight will arise from these cankers year to year. Active blight cankers are characterized by an amber or brown exudate on their surfaces or on the bark below. They often begin at the bases of blighted spurs, shoots, and suckers. This is true of susceptible pears, especially Bartlett, Bosc, and Red Clapp's, and certain apple rootstocks, especially M.26 and M.9.Ĭankers, slightly sunken areas of various sizes surrounded by irregular cracks, occur on small to large limbs, trunks, and even roots. Suckers at the base of trees are often invaded and may blight back to the trunk or rootstock, causing the loss of the entire tree in one season. Infected branches may be girdled, resulting in loss of the entire branch. Inside these droplets are millions of bacteria, which may cause new infections.įire blight bacteria can move from blighted spurs and shoots through the vascular system into larger limbs and tree trunks. Pearly or amber-colored droplets of bacterial ooze are often present on diseased blossoms, fruit, and leaf stems, on succulent shoot stems, and on the exterior of infected fruits.

A characteristic symptom of shoot blight is the bending of terminal growth into the shape of a shepherd's crook. The leaves wilt rapidly, turn dark, and remain attached as in the case of spur blight. It may occur any time during the season while the shoots are still growing and when environmental conditions are most favorable for the disease. Shoot blight begins with the infection of the young, succulent growing tip. Some remain even after normal leaf fall.įire blight's two main symptoms are shoot blight and cankers on limbs. The blighted flowers and leaves remain attached for much, if not all, of the growing season. The leaves wilt, turning brown on apples and quince and dark brown to black on pear. Here they follow the midrib and main veins, which soon darken. Bacteria may move through the pedicel to the fruit spur and out into the leaves. Infected blossoms wilt rapidly and turn light to dark brown. The disease gains entry to the tree through two main points, blossoms and new shoots, and often appears first in spring as blossom, fruit spur, and new shoot blight.

Some susceptible varieties include Braeburn, Crimson Crisp, Fuji, Gala, Granny Smith, Jonathan, Rome, Yellow Transparent, and Idared. Certain varieties of apples are more susceptible than others. In fruit trees, the disease can kill blossoms, fruit, shoots, limbs, and tree trunks. Fire blight also occurs frequently on pyracantha, spirea, hawthorn, and mountain ash.

Streptomycin fruit tree spray