Click on any
image for a more
detailed view

Symptoms and Signs

Symptoms of fire blight can be observed on all above ground tissues including blossoms, fruits, shoots, branches and limbs, and in the rootstock near the graft union on the lower trunk. Generally, symptoms of fire blight are easy to recognize and distinguishable from other diseases.

Blossom clusters and young shoots

Blossom symptoms are first observed 1-2 weeks after petal fall. The floral receptacle, ovary, and peduncles become water soaked and dull, grayish green in appearance. Later these tissues shrivel and turn brown to black. Similar symptoms often develop in the base of the blossom cluster and young fruitlets as the infection spreads internally (Figure 2). During periods of high humidity, small droplets of bacterial ooze form on watersoaked and discolored tissues (see example on fruit, Figure 7). Ooze droplets are initially creamy white, becoming amber tinted as they age.

Figure 2

Figure 7

Shoot symptoms

Shoot symptoms are similar to those in blossoms but develop more rapidly. Tips of shoots may wilt rapidly to form a "shepherd's crook" (Figures 1 and 3). Leaves on diseased shoots often show blackening along the midrib and veins before becoming fully necrotic. Numerous diseased shoots give a tree a burnt, blighted appearance, hence the disease name (Figure 4).

Figure 1

Figure 3

Figure 4

Advanced foliar symptoms

Infections initiated in blossoms and shoots can continue to expand both up and down larger branches and limbs. Bark on younger branches becomes darkened and water-soaked (Figure 5). At advanced stages, cracks will develop in the bark, and the surface will be sunken slightly (Figure 6). Amber-colored bacterial ooze mixed with plant sap may be present on bark. Wood under the bark will show streaked discolorations.

Figure 5

Figure 6

Pear and apple fruits

Indeterminate, water-soaked lesions form on fruit surface and later turn brown to black. Droplets of bacterial ooze may form on lesions, usually in association with lenticels (Figure 7). Severely diseased fruits blacken completely and shrivel.

Apple rootstocks

Rootstock infections usually develop near the graft union as a result of internal movement of the pathogen through the tree or from infections through water sprouts or burr knots. The bark of infected rootstocks may show water-soaking, a purplish to black discoloration, cracking, and signs of bacterial ooze. Red-brown to black streaking may be apparent in wood just under the bark (Figure 8). Symptoms of rootstock blight can be confused with Phytophthora collar rot. Malling 26 and 9 rootstocks are highly susceptible to fire blight.

Figure 8

RETURN TO TOP