Return to main tree page  AVTreeFarm   Fire Blight

 The bacteria spread down through the flowers into the twigs and branches, where cankers develop. In many cases, developing cankers encircle a shoot or branch by midsummer, causing conspicuous branch and twig dieback. Although fireblight is spread primarily through flower infection, leaves and twigs damaged by hail or wounded in some other manner are also susceptible. Tender, succulent shoots and sprouts are also vulnerable to infection. Although severely diseased trees may be killed, usually only the fruiting stems die. The result is greatly reduced fruit yield. Fireblight is most severe during wet weather from 65° to 85° F.


SOLUTION: After the infection has stopped spreading in the summer or fall, prune out and destroy infected twigs and branches at least 12 inches beyond visible decay. Sterilize pruning shears with rubbing alcohol after each cut. A protective spray of basic copper sulfate or streptomycin, applied before the blossoms open next spring, will help prevent infection. Respray at intervals of 5 to 7 days until the end of the blooming period. To prevent excess growth of shoots and suckers, avoid high-nitrogen fertilizers. Plant fireblight-resistant varieties.It's hard to even think it, but Spring sometimes can be a mixed blessing.

Fire blight thrives in warmer, wet weather when the disease-causing bacterium becomes active. Apple, pear, quince, crabapple and mountain ash, but NOT GREEN ASH, commonly are affected. The bacterium oozes out of cracks and crevices in the bark, and bees or other pollinating insects pick it up on their bodies.   

The disease spreads as these insects pollinate other flowers.If your trees are affected by fire blight, they will begin to show symptoms just before their flower petals fall. This is the blossom blight stage when flowers begin to turn brown and mushy and wilt. Eventually, the bacteria will move down into the branches and leaves of the tree. Leaves darken and wilt but remain attached to the tree (see above), giving it a scorched or burned look. Branch tips blacken and curl, causing a "shepherd's crook" symptom.

Fruit also can be affected. Bacteria often oozes out of the infected fruit and, as symptoms progress, fruits remain attached to the tree as shriveled "mummies" (see above). Cankers, which are sunken areas darker in color than the surrounding bark, form as the disease progresses. If present on the main trunk, cankers often are fatal, as they eventually will girdle the tree.

Canker  on trunk of mountain ash

fireblight infected blossoms

fireblight twig

Leaf Fireblight

Cankers also serve as the over wintering source of the bacterium. The following spring, bacteria will ooze from the cankers or cracks in bark. Insects may come in contact with the ooze and spread the disease to other trees.

Fire blight control can be a challenge. A variety of controls are available and success usually is greatest when we integrate all of them.

The use of resistant varieties is the first line of defense. Listed on the table below are apple and crabapple trees with certain degrees of resistance to the blight. Resistance doesn't necessarily mean immunity. A tree with resistance can become infected, but the problem won't be nearly as severe as if there were no degree of resistance.

Avoid over fertilization with nitrogen. Nitrogen stimulates new growth and the new growth is highly susceptible to fire blight infection.

Practice sanitation when pruning trees. Prune out and destroy all infected and dead plant tissue. Make pruning cuts 6 to 12 inches into healthy tissue. Always dip tools in a disinfectant solution, such as 10 percent household bleach, between each cut to minimize disease spread. Prune newly infected twigs as soon as possible in the spring. Do all other pruning during winter.

You may want to spray next spring to prevent the infection. Chemicals will have little or no effect on existing infections. Copper compounds, such as Bordeaux mixture, Kocide or lime sulfur, or streptomycin (Agristrep) are effective chemicals. Timing, however, is critical. If you use copper, you must apply during dormancy and bud break. Copper may burn leaves and fruit if it is applied later in the season. If you use streptomycin, apply when bloom is 50 percent and repeat twice at 4-to-5 day intervals.

Tree varieties with some degree of fire blight resistance*

* Resistance does not mean immunity.

On Crab Apple
PROBLEM: Blossoms and leaves of some twigs suddenly wilt and turn black as if scorched by fire. Leaves curl and hang downward. The bark at the base of a blighted twig becomes water-soaked, then dark, sunken, and dry; cracks may develop at the edge of the sunken area. In warm, moist spring weather drops of brown ooze appear on the sunken bark.

ANALYSIS: Fire blight This plant disease is caused by a bacterium (Erwinia amylovora) that is extremely destructive to many trees and shrubs. Bacteria of this species spend the winter in the sunken areas (cankers) on the branches. In the spring, the bacteria ooze out of the cankers and are carried by insects to the plant blossoms. Flies and other insects are attracted to the sweet, sticky ooze and become smeared with it. When the insects visit a flower for nectar, they infect it with the bacteria. Bees visiting these infected blossoms carry bacterialaden nectar to healthy blossoms. Rain, wind, and tools may also spread the bacteria. Fireblight spreads rapidly through plant tissue in humid weather above 65 ° F.


SOLUTION: During spring and summer, prune out infected branches about 12 inches beyond any visible discoloration; destroy the branches. Sterilize the pruning tools with rubbing alcohol after each cut. Before bud break in the spring, spray with a pesticide containing basic copper sulfate or streptomycin; this will help prevent infection. Respray at intervals of 5 to 7 days until the end of bloom. In summer or fall, after the disease stops spreading, prune out infected branches.

Some plants susceptible to fireblight:

Botanical name                 Common name

TREES AND SHRUBS
Amelanchier                     Serviceberry
Chaenomeles                    Flowering quince
Cotoneaster
Crataegus                         Hawthorn
Eriobotrya                        Loquat
Malus Apple,                    crab apple
Photinia
Prunus                             Flowering almond, plum, and cherry
Rosa                                Rose
Sorbus                             Mountain ash
Spiraea

FRUIT TREES AND BERRIES
Apple
Pear
Quince
Raspberry

PYRACANTHA PROBLEM: Blossoms and leaves of some twigs suddenly wilt and turn black as if scorched by fire. The leaves curl and hang downward. The bark at the base of a blighted twig becomes watersoaked, then dark, sunken, and dry; cracks may develop at the edge of the sunken area. In warm, moist spring weather, drops of brown ooze appear on the sunken bark. Young plants may die. ANALYSIS: Fire blight This plant disease is caused by a bacterium (Erwinia amylovora) that is extremely destructive to many trees and shrubs. Bacteria of this species spend the winter in sunken areas (cankers) on the branches. In the spring, the bacteria ooze out of the cankers. Bees, flies, and other insects are attracted to the sweet, sticky ooze and become smeared with it. When the insects visit a flower for nectar, they infect it with the bacteria. Insects visiting these infected blossoms later carry bacteria-laden nectar to healthy blossoms. Fireblight spreads rapidly through plant tissue in humid weather above 65 ° F. Tender or damaged leaves may be infected in midsummer.

SOLUTION: During spring and mid- to late summer, prune out infected branches 12 to 15 inches beyond any visible discoloration; destroy the branches. A protective spray of a bactericide containing basic copper sulfate or streptomycin, applied before bud break in spring, will help prevent infection. Respray at intervals of 5 to 7 days until the end of bloom. In the fall, prune out infected branches. Sterilize pruning shears with rubbing alcohol after each cut.

Some species of pyracantha and hawthorn tolerant of fireblight:

Botanical name                     Common name
PYRACANTHA
P. coccinea 'Lalandei'             Laland's firethorn
P. fortuneana


HAWTHORN
Crataegus                             Washington
phaenopyrum                         hawthorn


Some avocado varieties for California and Florida, from most hardy to least hardy:
For California 
Bacon                     
Zutano 
Fuerte 
Hass 

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Fungicides for Fire blight

BASIC COPPER SULFATE, TRI-BASIC Mfg: 
Cities Services, Phelps Dodge, 
CP Chemical and others:
Alternaria leaf blight, angular leaf spot, Anthracnose, apple blotch, apple scab, bacterial blight, bacterial canker, bacterial leaf spot, bacterial wilt, bitter rot, black rot blight, blossom rot, blue mold, brown rot, brown rot blossom blight, Cercospora blight, Cercospora leaf spot, citrus scab, downy mildew, early blight, fire blight, greasy spot, gummy stem blight, late blight, leaf blight, leaf curl, leaf mold, leaf spot, melanose, nail head rust, peach blight, peach leaf curl, peacock spot, Phomopsis, pink pitting, powdery mildew, purple blotch, red alga, scab, Septoria leaf spot, Septoria rot, shot hole, smut, Stemphylium leaf spot, walnut blight, white rust, yellow rust.

BORDEAUX Mfg: Numerous
Angular leaf spot, Anthracnose, bacterial blight, bacterial wilt, bitter rot, black pit, black rot, blossom blight, blotch, brown rot, cane blight, canker gall, Cercospora leaf spot, crown gall, downy mildew, fire blight, frogeye leaf spot, green rot, gummosis, leaf blight, leaf mold, melanose, peach blight, peach leaf curl, rust, scab, shot hole, white mold, wildfire.

COPPER HYDROXIDE, BLUE-SHIELD, KOCIDE
Mfg: Kocide Chem., and Others:
Algae, Alternaria blight, angular leaf spot, Anthracnose, bacterial blast, bacterial blight, bacterial leaf blight, bacterial leaf streak, bacterial spot, ball moss, Botrytis blight, brown rot, carrot blight, Cercospora leaf spot, collar rot, common blight, common bunt, cornyeum blight, crown rot, dead bud, downy mildew, early blight, European canker, fire blight, greasy spot, halo blight, Helminthosporium spot blotch, 
iron spot, late blight, leaf blotch, leaf curl, leaf rust, leaf spot, melanose, peacock spot, phomopsis, pink disease, pink pitting, pseudomonos leaf spot, purple blotch, scab, seed rot, septoria leaf blotch, shot hole, sigatoka, Votutella leaf blight, walnut blight, water mold, xanthomonas leaf spot.

COPPER OXYCHLORIDE SULFATE, COCS
Mfg: FMC & Others:
Angular leaf spot, Anthracnose, bacterial spot, black rot, brown rot, bud blight, Cercospora leaf spot, cherry leaf spot, Coryneum blight, damping-off, downy mildew, early blight, fire blight, greasy spot, late blight, leaf blight, Macrosporum leaf spot, melanose, peach blight, peach leaf curl, pod spot, powdery mildew, scab, Septoria leaf spot, shot hole, tar leaf spot, twig blight, walnut blight, yellow rust.

MYCO-SHIELD Mfg: Pfizer
YTD in citrus, bacterial spot, fire blight, ice nucleating bacteria.

STREPTOMYCIN Mfg: Pfizer & Merck
Bacterial blight, bacterial spot, bacterial wilt, black leg, blue mold, fire blight, soft rot, 
wildfire.

TERRAMYCIN Mfg: Pfizer
Bacterial spot, fire blight, lethal decline, lethal yellowing disease, pear decline, 
X-disease.

ZINC COPOSIL, CUPRIC ZINC SULFATE COMPLEX
Mfg: Numerous
Anthracnose, brown rot, bunch rot, Cercospora leaf spot, downy mildew, early and late blights, fire blight, leaf curl, leaf spot, powdery mildew, scab, Septoria, shot hole, walnut blight.

ZINEB Mfg: Rohm & Haas
Alternaria leaf blight, Alternaria spp., Anthracnose, apple blotch, bitter rot, black rot, blue mold, Botrytis blight, Botryosphaeria fruit rot, Brooks spot, cedar rust, Cercospora early blight, Cercospora leaf spot, cobweb, Dactylium spp., damping-off, downy mildew, early blight, fading-out, fire blight, flyspeck, frogeye leaf spot, fruit rot, fruit russet, Fusarium seed decay, Fusarium seed piece decay, Fusarium spp., gray leaf spot, greasy spot, green mold, Helminthosporium blight, late blight, leaf rust, leaf spot, mildew, Mycogone (bubbles), Mycogone spp., peach leaf curl, pecan scab, petal blight, Phomopsis spp., Phytophthora, Phythium blight, quince rust, ripe rot, rust, scab, Septoria late blight, Septoria leaf spot, shot hole, slime mold, sooty blotch, soreshin, stem rust, Southwestern cotton rust, Trichoderma spp., Verticillium spp., white rust.