Why Does My Pear Tree Have Fire Blight?

Fire blight is one of the most destructive diseases that can affect a pear tree, and it moves fast. Within a few weeks of infection, entire branches can die, and in severe cases the disease can kill a tree. Recognising fire blight quickly and responding immediately is the difference between losing a branch and losing the tree.

How fire blight spreads and enters the tree

Fire blight is caused by the bacterium Erwinia amylovora. It overwinters in cankers on infected wood and in early spring produces a bacterial ooze that smells faintly of fermentation. Insects, birds, rain splash and pruning tools carry the bacteria from cankers to open blossom. Once inside the flower, the bacteria multiply rapidly and move down through the blossom stem into the spur, branch and eventually the main trunk. Warm, humid conditions around petal fall — temperatures above 18°C with rain or heavy dew — create the highest infection risk.

Identifying the symptoms

Infected blossom turns brown and remains hanging on the branch. Shoot tips wilt and curve over. Leaves on infected shoots turn brown or black but do not fall — a distinctive "blighted" appearance that gives the disease its name, as if the shoot has been burned. Cut back into an infected branch and the wood shows a characteristic reddish-brown streaking in the vascular tissue that continues back beyond the visible symptoms. In wet weather, small droplets of cream-coloured bacterial ooze may appear on cankers.

Pruning out infection

Cut all infected wood at least 30 cm back into clean, unaffected wood — more if the reddish staining extends further. Make cuts at a slanted angle on a dry day. Sterilise cutting tools between every single cut using a 10% bleach solution or methylated spirits — fire blight is easily carried from one cut to the next on contaminated blades. Bag all removed material and burn or dispose of it in household waste. Do not compost it under any circumstances.

Prevention through variety and management

Some pear varieties have better fire blight resistance than others. Highly susceptible varieties include Williams and Conference in certain conditions. Avoid feeding trees with high nitrogen, which produces the soft, fast-growing shoots that fire blight colonises most easily. Avoid working in the tree in wet weather when bacterial ooze is active. In orchards where fire blight is a persistent annual problem, removing alternative hosts (crab apples, hawthorn, rowans) from the immediate area reduces the overall inoculum load.