Fire blight is the disease pear growers worry about most, and for good reason. It is caused by a bacterium, Erwinia amylovora, that can run from a blossom or a shoot tip down into the branch and, on a susceptible tree, all the way to the trunk. The good news is that you can usually stop it with careful, well-timed pruning and a few changes in how you care for the tree.

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The short answer: if shoot tips on your pear wilt, turn black and bend over like a shepherd’s crook, with dead leaves still hanging on, it is almost certainly fire blight. Cut infected shoots at least 12 inches below the visible damage in dry weather, get the cuttings out of the yard, avoid heavy pruning and high-nitrogen fertilizer, and plant resistant varieties next time.

How to recognize fire blight

The University of Minnesota Extension lists the signs to look for:

Blossoms that look water-soaked, then wilt and turn brown or black, often staying on the tree.
Young shoots that wilt and bend at the tip into a hook, a shape often called a shepherd’s crook.
Leaves that turn brown to black and stay attached to the twig, sometimes into winter. A badly hit tree looks scorched by fire, which is where the name comes from.
Sunken, dark, cracked bark (cankers) on branches or the trunk, sometimes with cream to amber droplets of ooze in humid weather.
Fruit that turns dark and shrivels on the branch.

Sign	Fire blight	Look-alike
Shoot tip bent into a hook, blackened	Yes, classic sign	Drought wilt does not usually blacken
Dead leaves stay attached	Yes	Frost-killed leaves often drop
Orange spots on leaves	No	Pear trellis rust
Oozing droplets from bark in warm, wet weather	Often	Cankers from other causes

How it spreads

The bacteria spend the winter at the edges of old cankers. In warm, wet spring weather, generally above 65°F, they multiply and seep out as sticky ooze. Insects, including pollinators, carry them to open blossoms, and rain splash and pruning tools move them around too. Once inside, the bacteria can travel through the tree’s vascular system into larger branches.

That is why fire blight tends to be worse in years with warm, rainy weather at bloom, and why fast, soft new growth is especially vulnerable.

Pruning fire blight out

Pruning is the main tool for home gardeners. The guidance from the University of Minnesota Extension is specific:

During the growing season, cut infected shoots at least 12 inches below the last visible sign of infection, in dry weather.
For cankers on larger limbs, prune in late winter while the tree and the bacteria are dormant, cutting through healthy wood at least 8 inches below the discolored bark.
If every cut is in clearly healthy wood, the tools only touch clean tissue. If you are unsure, dip or wipe the blades in rubbing alcohol or a household disinfectant between cuts.
Bag or remove all prunings from the property. Do not leave them in a pile near the tree.

If the infection has reached the main trunk, the disease is unlikely to be stopped. The Minnesota guidance is that the tree will eventually die, and removing it helps protect nearby susceptible trees.

Prevention that works

Go easy on nitrogen. Heavy fertilizing pushes out lush, soft shoots, which are the easiest targets. Use a soil test before feeding a pear at all.

Avoid heavy pruning. Large cuts in one year trigger a flush of vigorous water sprouts. Penn State Extension’s fruit-pruning advice is to make the main structural cuts while the tree is dormant and to keep annual pruning moderate.

Remove old cankers in winter. Each canker is a source of next spring’s bacteria.

Choose resistant varieties. No pear is immune, but some are much more tolerant than others. ‘Bartlett’ is known to be susceptible. Ask a local nursery or your extension office which resistant varieties do well in your area before you plant.

About sprays. Some products labeled for fire blight can reduce blossom infection when timed to bloom, and they are mostly used in commercial orchards. They do nothing for existing cankers. For a backyard tree, pruning and cultural care are the core of control. Always follow the label exactly if you use one.

Is it fire blight or something else?

Bright orange spots on the leaves point to pear trellis rust, a fungal disease linked to junipers. Brown leaf edges and blotches can be scorch, a leaf spot or a mite problem; see why pear leaves turn brown. Amber gum on the trunk of a peach or cherry is a different set of problems, covered in why a peach tree oozes sap.

When to call a certified arborist

Call a certified arborist if the infection has reached large limbs or the trunk, if the tree is too tall to prune safely from the ground, or if several trees in the yard are affected. For a sample diagnosis, your county extension office can help. To find a certified professional, use the ISA Find an Arborist directory.

More fruit tree guides are in the Fruit Trees hub.

Sources

Fire Blight, University of Minnesota Extension
Fire Blight, The Morton Arboretum
Pruning Fruit Trees, Penn State Extension

Top photo: Ninjatacoshell, CC BY-SA 3.0, via Wikimedia Commons

Fire Blight on Pear Trees: How to Prune It Out and Prevent It