Fire Blight on Ornamental and Fruit Bearing Trees

Fire Blight
Fire Blight. University of Tennessee

Disease Description

Fire blight is a serious disease of apple, pear and plum quince. This disease occasionally damages cotoneaster, crab apple, hawthorn, mountain ash, ornamental pear, firethorn, spiraea and other pome fruited trees. Fire blight, caused by the blight bacterium Erwinia amylovora, can affect many parts of a susceptible plant but generally noticed first on damaged blighted leaves.

The bacterium, Erwinia amylovora, overwinters in trunk and branch cankers.

As spring temperatures increase when the weather is sufficiently warm and as moist-rooted trees resume growth, some cankers start to resume activity as the bacteria grows. This spring warm up triggers the bacteria to resume multiplication and when temperatures are above 65 F.

You can find oozings from branch or twig surfaces which are light tan in color. Splashing rains and traveling  insects transmit the bacteria to neighboring flower blossoms and susceptible succulent growing shoots. Once blossoms are contaminated with the bacteria, nectar-seeking bees become effective carriers of the pathogen.

Disease Symptoms

The name “fire blight” describes the most characteristic symptoms of this disease: a brown-to-black scorched appearance of twigs, flowers and foliage. It is, as I mention, usually seen first in spring when blossoms and fruit spurs appear water-soaked, wilted, shriveled and finally turn brown to black.

Shoot blight occurs when infections begin at shoot tips, moving rapidly down the shoots and then to limbs and trunk. Apple and crabapple leaves turn brown, pear leaves turn black. Frequently, the tip of the blighted shoot bends over and resembles a shepherd’s crook.

Dead, blackened leaves and fruit can persist on branches during the entire growing season.

This look gives the tree a scorched appearance where it gets the name “fire blight.”

Disease Control

A combination of pruning, reduced fertilization and chemicals can help control fire blight.

Prune and remove all stems showing symptoms. Cut back into the healthy portion of both stems and limbs. You will increase your success if the removal of fire blight infections is done in summer or winter when the bacteria no longer are spreading through the tree. You will also limit the spread if you limit pruning during the period of bacterial growth.

Over-fertilization will cause rapid new growth which is most susceptible to the blight. Moderate your fertilizer application to reduce rapid tree or shrub growth. Over-pruning can have the same effect of creating excessive growth so you should refrain from heavy spring pruning.

If you have seen fire blight on a tree in the past, chemicals could help on high-value trees.  Applying blossom sprays will help prevent new infections but won’t eliminate wood infections. Cankers must be pruned out. The antibiotic streptomycin is the most effective spray material for controlling fire blight. It will prevent but not control infections. Use streptomycin in spring during bloom.

Resistant Varieties

Apple, pear, crab apple, ornamental pear and pyracantha have resistant varieties to fire blight. You need to stick with these varieties when planting. Check your planting stock for fire blight resistance.