Fire Blight

Fire Blight

Signs of Fire Blight on a Pear tree.

What is it?

Fire Blight is a disease that usually attacks Apples and Pears. It's caused by a bacteria that survives the winters in branch and trunk cankers(1). Once springtime rolls around, the bacteria begins multiplying once the temperature is above 65 degrees.

Infected trunk of an Apple tree

Do you have it?

You can sometimes see the white, liquid bacteria oozing out of cankers on the tree. It is called Fire Blight because of the symptoms it causes. It will look like the leaves, flowers, and small twigs have been scorched away. You'll usually notice the symptoms rather early in the year.

What does it do?

The infection starts in tip shoot tips and moves downward all the way to the trunk. The leaves will start turning brown or black, depending on the type of tree it is. (apples and crab apples usually turn brown, pear trees look black.) The disease will also infect fruit. This next picture is an apple infected with fire blight.

That's bacteria seeping out of it... gross.

The areas most commonly affected are the open flowers in the spring. It sometimes stays local to a certain part of the tree, but sometimes will spread to other areas. It can kill susceptible trees and even if it doesn't kill it, it can severely disfigure it. Once the tree has fire blight, it stays forever.

How to manage it:

Fire Blight can be avoided by planting certain types of trees that aren't affected by it. For example, if you want to plant a pear tree, you would want to avoid Asian and Red pears as they are the most susceptible.

If you've already got the trees then there are some tips to preventing the infection from spreading.

• Do not use excess nitrogen fertilization
• Do not prune if you can help it
• The tree should not be irrigated during the bloom cycle
• If you see an area that is showing symptoms of blight, remove and destroy it immediately
• With no cure known yet, the recommended spray to help would be a Copper blossom spray. It stops new infections, but it's detrimental that you cut the old infections out as best as you can.
• These sprays should be applied the entire time the tree is in the blossom stage, and should be applied when the temperature is above 60 degrees. Do this every 4 to 5 days until the bloom is over. This could mean as many as 12 treatments in one year.
• When trimming out infected areas, make SURE you clean your clippers after every snip. A bucket with 10% bleach in it will be fine.
• The best times to trim is in the summer and winter. During these seasons the infection has stopped reproducing and is dormant, thus making it easier to find the infection and destroy it.

(1) A canker on a tree is a small or large portion of dead bark that was killed during the previous years' infection.