Leaves, branches and flower clusters turn a distinctive reddish-brown, as though scorched, and infected stem tips curl over into a shepherd’s hook: this is fire blight (Erwinia amylovora), the bacterial disease that can decimate an apple or pear orchard in months. No cure exists, so everything rests on cutting well beyond the infection and disinfecting tools between cuts.
| Botanical name | Erwinia amylovora |
|---|---|
| Common name | Fire blight bacterial disease |
| Symptoms | Wilting flowers, cankers, sticky goo |
A terrifying disease in orchards where it attacks apple trees, pear trees and other species of the same family, fire blight can quickly decimate an entire plot if you don’t deal with it fast enough.
The Erwinia amylovora bacteria is what causes fire blight. This particular disease will only infect plants that are part of the Rosaceae family: apple tree, pear tree, cotoneaster, rowan or mountain ash (Sorbus), hawthorn (Crataegus), photinia (Photinia or Stranvaesia) and firethorn (Pyracantha).
Note that some Rosaceae plants seem invulnerable to fireblight, especially stone fruit trees such as plum, cherry, peach and nectarine trees.
The disease probably originated in North America nearly 200 years ago, then spread to Europe in the mid-1900s. Ever since, local agriculture offices constantly monitor its spread. In some countries, fire blight is the reason there’s a ban on import, planting and trade of specific plant species. Indeed, such species facilitate fire blight contamination and spread.
First of all, to control fire blight, it’s important to recognize symptoms of the disease:
The key characteristic of bacterial fire blight is that it spreads extremely fast. A branch is a goner within days, and an entire tree might only survive a couple months.
Fire blight shows itself in several different ways, and spotting the right one early decides whether you save the tree. Use the table below to match what you see to the part of the plant affected.
| Symptom | Where it appears | What you see |
|---|---|---|
| Cankers | Branches and trunk | Bulges of dying bark |
| Sticky ooze | Out of the cankers, mostly in rainy weather | White droplets seeping out |
| Wilting bloom | Flowers, during the blooming season | Flowers wilt then die off entirely |
| Aborted shoots | Young shoots, via the inner bark (phloem) | Shoots stop growing and abort |
| Burned look | Leaves, branches and flower clusters | A very distinctive reddish-brown |
| Shepherd’s hook | Stem tips on some species | Tip curled like a candy cane |
Whatever the symptom, the response is the same: cut well back into healthy wood and burn what you remove.
Similarly to other fungal and bacterial diseases, conditions that most trigger the spread of fire blight are warm temperatures and moisture in the air. That’s when cankers produce the most ooze. This in turn speeds spread of the bacteria, Erwinia amylovora, carried away by birds, rain, wind, insects, etc.
The disease is active from Spring to Fall, and flares up during vegetation phases. Fireblight spreads particularly fast after the blooming since the bacteria enters plants through tiny wounds left on flower stems as the wilting petals break off. Of course, when pruning and trimming, each cut is like an open door through which the invader can come charging in.
To this day, there isn’t any curative treatment against fire blight, either natural or chemical. The only way forward is prevention. Through certain practices, you can protect plants and safeguard your orchard from contamination.
Important: the only effective way to destroy plant material infected with fire blight is to burn it. Also, take great care to disinfect all your tools, gloves, and clothes, even if you feel you haven’t used them. This is actually a good habit to take even when you’re not trying to fight off an infection.
