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What is Fire Blight? One of the worst pear and apple tree diseases

By: Lacey Russell, PhD | May 18th, 2018

Is something not quite right with your pear or apple tree? Do the flowers looks water soaked? Have the twigs turned black, shriveled up, and formed the shape of a shepherd’s crook? Do your once green leaves look like they’ve been burnt at the tips? If so, your tree may be the victim of a disease called fire blight.

What is fire blight?

Fire blight, one of many tree diseases, is a disease that begins when bacteria called Erwinia amylovora enters the plant and begins to move through its water conducting system. As it spreads through the tree, it clogs up the plant and prevents the flow of water and nutrients. It can destroy shrubs, tree limbs, or entire trees.

Learn how to identify Texas tree diseases on your own

What kind of trees get fire blight?

The disease is mostly found in trees and shrubs of the botanical family Rosaceae (the rose family). This includes pear trees, apple trees, flowering quince, hawthorns, firethorn (pyracantha,) and of-course, rose bushes. Shrubs, herbs, strawberries, figs, and mulberries are also in the rose family. But of all the family members, pear and apple tree fire blight tends to be most common and severe.

Fire blight is one of the biggest killers of commercial apples and pears. An entire orchard can look like it was literally scorched by fire.

In ornamental pear trees it's a problem as well—including the Bradford pear. It's less common on hawthorn, spirea, cotoneaster, red-tip photinia, loquat, mountain ash and other related plants.

How does fire blight spread?

Fire blight enters plants and trees through flowers—when bees or other pollinating insects visit for a sip of nectar. It can also enter through wounded areas of a tree.

The bacteria that causes fire blight loves warm and humid temperatures. It multiplies and spreads when conditions are right. These bacteria thrive in warm and wet springs because the flowers of their favorite plants and trees are open and begging for infection.

Fire blight spends the winter in bud scars, branches, and cankers formed by the bacteria. From the cankers, the bacteria creates an amber-colored ooze that attracts insects that then spreads the bacteria to more flowers.

Rain also spreads fire blight by splashing onto the bacterial ooze and causing new infections.

what does fire blight look like?

LEARN TO IDENTIFY  TEXAS TREE DISEASES DOWNLOAD THE FREE GUIDERemember that the bacteria most often enters the plant through the flowers (more specifically the nectar producing glands, or nectaries). Once infected the flowers will start turning brown and die. They will hang limp from the tree and appear water soaked.

Next the disease spreads to the limbs, twigs, and leaves of the tree. The infected parts of the tree will eventually turn black or brown and die. Sometimes the middle vein on a leaf will turn black before it shrivels and dies. The leaves will remain on the tree after dying.

New growth shoots will turn black and curl, giving the appearance of a “shepherd’s crook.” These new shoots become infected a week or so later than the flowers. What's weird is that some shoots stay completely unharmed by the disease.

And last, but not least, developing fruits will wither and die.

Click here to see some symptoms of fire blight.

Bacterial ooze. If weather is warm and wet the affected shoots begin to weep and ooze sticky, amber-colored goo, which is full of the bad bacteria. The wood under this ooze will become discolored and develop large sunken cankers that will eventually enlarge and girdle the branches, killing the branch.

fire blight treatment

The one positive of fire blight disease is that it moves slowly and can be controlled if detected early enough.

Contact a tree health specialist if you want help determining if your trees have fire blight. They can keep it under control and prevent it from spreading to the rest of the tree, or infecting other trees. If a tree is not treated, the infection will spread to wood from the previous year’s growth. At this stage, the tree will almost certainly die.

Prune in the winter

Because the disease moves slowly, it's possible to remove infected branches and save the rest of the tree. During the winter when the trees are dormant, prune the diseased limbs to remove infected wood. Prune the branches at least 8 inches below the damage. When you remove a diseased shoot, remove them as close to the branch as possible.

Inspect them for cankers. These are darkened, shriveled, sunken areas of the stems. The bacteria will be hiding below the cankers, which is why you’ll want to prune below the obvious cankers.

Avoid pruning when the plants are wet as this may spread the disease. It is also very important that you dip your pruners in a solution of 70 percent isopropyl alcohol (rubbing alcohol) or a 10 percent bleach solution between each cut. If you don’t take this precaution you risk spreading the disease to unaffected parts of the plant.

Reduce water and ferilization

This may seem counterintuitive, but reduce water and fertilization to the plant. You don’t want to encourage new growth, as the bacteria love succulent and tender shoots.

fire blight spray

Reduce new infections by spraying an antibiotic on flowers or shoots before the bacteria infect them.

A product that includes streptomycin sulfate has been shown to prevent fire blight infections.

Copper sulfate fungicide is also an option for preventing infections but requires you to spray weekly through the spring (while the blooms are open).

How can I prevent fire blight from infecting my trees?

Find out from your neighbors if fire blight has been a problem in your area.

The best way to fight tree disease is for neighborhoods to join forces. Educate your neighbors about fire blight if they are growing apples, pears, or flowering quince.

Preventative sprays

If you are growing apple, pear, or flowering quince, you may want to consider antibiotic sprays during warm and wet springs to prevent infection.

Proactive disease removal

Be on the lookout for the symptoms, so you can quickly remove any diseased parts of the tree.

Plant moderately resistant varieties.

No pear or apple trees are 100% resistant to fire blight, but some varieties have shown stronger resistance than others. The agrilife extension service recommends several pear trees for Texas growers. Click here to learn more about edible pear varieties for Texas.

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