Fire blight

What it is

A bacterial disease, Erwinia amylovora

Trees affected

Pear, apple, crabapple, quince, firethorn, hawthorn, cotoneaster, mountain ash

Where in our area

Fruit trees and ornamentals on lots at any elevation, about 4,000 to 6,500 feet

Key sign

Blackened blossoms and shoots, hooked shoot tips, leaves stuck on the twig

Spread

Insects, rain, wind, contaminated pruning tools

Fire blight is a disease of the rose family. Utah State University lists apple and pear as the main hosts and notes that crabapple, hawthorn, cotoneaster and pyracantha can be infected too. This page covers what to look for, which trees, what an arborist checks and when pruning or removal is the answer.

What does fire blight look like?

Blossoms, young shoots and fruit wilt and blacken, and the University of California describes pear flowers turning black and apple flowers turning brown. The shoot tip curls over into a shepherd's crook. Dead leaves and fruit cling to the branch and give a scorched look, and amber droplets of ooze can form on cankers. Under the bark of an infected limb, University of California notes pink to orange-red streaks, and cankers become sunken and cracked.

• Blackened, hooked shoot tips
• Dead leaves clinging to twigs
• Amber ooze on cankers
• Sunken, cracked cankers on limbs

Which trees and which elevations?

Utah State University says apple and pear are the most economically important hosts and lists crabapple, hawthorn, cotoneaster and pyracantha. The University of California adds quince as extremely susceptible and serviceberry and mountain ash as less commonly affected. In our area that means apple and fruit trees, flowering crabapple and Callery pear.

These are planted trees at any elevation. Valley lots at about 4,500 to 4,700 feet and Tahoe lots at 6,200 feet and up are both inside the range of hosts. Pears and apples are most susceptible at flowering, according to Utah State, so the trouble shows after bloom.

How does it spread, and why does it come back?

Utah State says insects, contaminated pruning or grafting tools, wind and rain splash all carry the bacteria, and sprinklers that wet foliage act like rain. The University of California notes that an infected plant carries the pathogen indefinitely.

That is why one visit does not always end the blight. Pruning heavily in early summer is discouraged because it stimulates soft, susceptible growth. See our fruit tree pruning guide.

What does an arborist check?

The arborist looks at how many shoots are blighted, whether cankers have formed on limbs and trunk and whether the bark under a limb shows reddish streaks. They check how far the disease has moved from the tip, and whether any single limb is girdled.

• Number of infected shoots and limbs
• Cankers on limbs or trunk
• Girdled limbs
• Overall structure of the tree
• Other trees of the same family nearby

When is pruning or removal the answer?

University of California says to prune in summer or winter when the bacteria are not actively spreading, with fast-advancing infections on very susceptible pear and some apples cut out as soon as they appear in spring. Utah State recommends cutting at least 8 to 12 inches below the visible infection and cleaning tools between cuts when working on active summer blight. Dormant-season cuts do not require that sterilizing, it adds.

Neither source gives a threshold for removing the whole tree. We remove when the trunk or main limbs carry cankers, when most of the crown is blighted, or when the tree is too far gone to hold its shape. University of California notes that a girdled limb must come off entirely.

What does Battle Born Tree Service do about fire blight?

Call 775.232.8243 or use the estimate form on this page. An ISA Certified Arborist looks at the tree on site, explains what is wrong and tells you whether the job is pruning out infected wood or removal. Credential WE-11728A is held by one of our two certified arborists. We identify the problem, prune out dead or hazardous wood and remove trees that cannot be saved; we do not spray, inject, fertilize or apply products.