Fire blight is caused by a bacterium, Erwinia amylovora, and it only attacks trees in the rose family. In North Texas that means ornamental and fruiting pears, apples and crabapples, loquats, hawthorns, and pyracantha. Oaks, elms, and pecans do not get it.
What it looks like
The classic sign is the shepherd's crook. A shoot tip wilts, bends over into a hook, and turns black or dark brown, as if someone held a lighter to it. The dead leaves usually stay attached, which is what gives a badly hit tree that scorched look. Look closely and the blackening often starts at a flower cluster or a young shoot and runs downward. In warm, wet weather you may find amber ooze beading on the bark. That ooze carries the bacteria.
Timing tells you a lot. Fire blight shows up in spring and early summer, after bloom. A tree that blacks out in August after a dry spell is more likely heat and drought stress. One that blacks out in February after a freeze is freeze damage. Fire blight follows the bloom, because that is when the bacteria get in.
How it spreads in a North Texas spring
The bacteria overwinter in cankers on the bark, then ooze out in spring when the tree blooms. Pollinators carry the bacteria from flower to flower, and rain and hail splash it from tree to tree. Our springs are warm and often wet, which is exactly the weather fire blight likes: temperatures in the 70s and 80s with rain or heavy dew during bloom.
Soft, fast growth is the other half of the problem. A pear tree pushed hard with nitrogen fertilizer puts out long, tender shoots in spring. Those shoots are easy for the bacteria to colonize, and the infection runs through them fast. The Bradford pear problems guide covers the rest of that tree's baggage.
Pruning it out: the part that actually works
There is no spray that cures fire blight once it is in the wood. What works is cutting it out, and doing it right. Cut at least 8 to 12 inches below the lowest blackened wood, into wood that looks clean and healthy all the way around the branch. The bacteria travel ahead of the visible damage, so a cut made right at the black edge leaves infection behind and the shoot blacks out again below your cut.
Disinfect your tools between every cut. A 10 percent bleach solution, rubbing alcohol, or a household disinfectant spray all work. Dip or wipe, then cut. Skip this step and your saw becomes the vector, carrying bacteria from one branch to the next. Bag the cuttings or burn them where burning is allowed. Do not compost them, and do not leave them in a pile under the tree. The pruning timing guide covers the general seasonal rules, but fire blight adds one of its own: remove active strikes as soon as you see them, but only on a dry day. Pruning in rain or heavy dew spreads the bacteria you are trying to remove.
Save the heavy structural work for winter, when the tree is dormant and the bacteria are not active. That is also the time to take out old cankers on larger limbs, the sunken, darkened bark patches where the bacteria spent the winter. If you are not sure whether a dark patch is a canker or just rough bark, the diagnosis guide walks through telling common problems apart.
What does not work
Canopy sprays applied after the shoots turn black do nothing. The bacteria are inside the tissue, not on the surface. Wound paint on pruning cuts does not stop fire blight either, and it can trap moisture under the coating. The wound dressing guide explains why paint is usually a bad idea on any cut. Fertilizer pushed at a sick tree is the third waste of money: it forces the exact soft growth the bacteria exploit. A stressed pear needs water during drought and mulch over the roots, not a nitrogen blast.
Antibiotic sprays get mentioned online every spring. In commercial orchards, streptomycin applied during bloom can reduce new infections. For a homeowner with one yard pear, it is not a practical cure: it needs bloom-time timing and repeat applications, and it does nothing for wood that is already infected. If a company offers to spray your already-blackened pear back to health, that is a sales pitch, not a treatment plan.
When to stop pruning and take the tree down
Some trees are past the point where pruning helps. A young pear with cankers wrapping the trunk will not outgrow them. A tree that loses a third or more of its canopy to strikes in one season, then repeats the same performance the next spring, is on a downhill track. At that point the honest move is removal and planting something that does not spend every spring fighting the same bacterium. The fruit tree care guide covers variety choices for yards that want fruit without the annual fire blight battle.
For a mature tree with a few strikes, the math is different. Cut the strikes out, clean your tools, hold off on fertilizer, and watch the next bloom season. One bad spring does not condemn a tree. Three bad springs in a row, with cankers spreading down the limbs, usually does. Keep notes on which limbs were cut and when, so you can tell whether the problem is shrinking or spreading. If you need a second set of eyes on a tree that keeps striking, start from the Melissa tree service page or the trimming page.
What does fire blight look like on a pear tree?
The shoot tips bend over into a hook shape called a shepherd's crook, and the leaves and young shoots turn black or dark brown, as if scorched by fire. The blackened leaves usually stay attached instead of falling. In wet spring weather you may also see amber-colored ooze on the bark. The damage often shows up weeks after bloom, starting at the flowers and moving down the shoot.
Can fire blight be cured with a spray?
No. Once the bacteria are inside the wood, no spray cures the infection. Copper or antibiotic sprays applied at bloom time can reduce new infections in some orchard settings, but they are not a homeowner cure for a tree that already shows blackened shoots, and they do not rescue infected wood. Pruning out the infected wood and stopping the conditions that spread it are what actually help.
How far back do I prune a fire blight strike?
Cut at least 8 to 12 inches below the lowest visible blackening, into wood that looks clean and healthy all the way around. The bacteria travel ahead of the visible damage, so cutting right at the black edge leaves infection behind. Disinfect your saw or pruners between every cut, and bag or burn the cuttings rather than composting them or leaving them under the tree.
When should I prune out fire blight?
Remove active strikes as soon as you see them, but only on a dry day, since wet conditions and wet tools spread the bacteria. Do the heavy structural pruning in winter, when the tree is dormant and the bacteria are not active. Avoid pruning for shape during a wet spring bloom period, and skip heavy nitrogen fertilizer that pushes soft, fast growth the bacteria love.