News release: Fireblight, Part I

Tim Baker, MU Extension Horticulture Specialist
102 N. Main, Suite 1, Gallatin, MO 64640
660-663-3232, bakert@missouri.edu

Release Date: July 24, 2014

Headline: Fireblight, Part I

Four years ago, I wrote a couple of columns on fireblight, a bacterial disease of apples, pears, and related species. While the disease is usually around to some degree, some years are worse than others.  This year fireblight has been a major problem all over the state.  I saw some pretty bad cases of the disease in Lafayette and Saline counties… and it has been reported elsewhere as well. So I thought that I better get the word out again on how to deal with this problem.  If left untreated, fireblight can devastate your trees. 

Fireblight overwinters in cankers in the tree, and is spread in the spring by insects which come into contact with the ooze coming from the cankers and windblown rain which scatters it.

The blossoms in early spring usually become infected first.  Pollinating insects carry the disease from flower to flower, after which the blossom turns brown and dies.  The petals and other flower parts usually remain attached.  New shoot growth in spring is also susceptible to infection.  Leaves at the shoot tips wilt and die, with the shoot curling back, forming a "shepherd's crook.”  Often a foot or more of the limb may be affected.  The leaves turn brown or black, and look as if they were scorched by fire, which is where the name "fireblight" comes from.

Other parts of the tree may become infected as well, including mature leaves and fruit.  Cankers can form on twigs, limbs, and the main trunks of trees.  If the bark has been wounded, bacteria can colonize the wounded area, causing a discolored and sunken appearance.  A sticky ooze will develop, which attracts insects and secondary fungi because of the high sugar content.

Fireblight can also affect the collar or the base of the tree at ground level.  Here it can move into the roots if given the opportunity.  In either area, it can easily kill the tree or cause severe structural damage.

The disease develops most quickly under conditions of frequent rains, when buds and shoots are developing rapidly, and when temperatures range from 60 to 75 degrees.  Infection can occur rapidly, and frequent scouting of susceptible trees is a must.

In my next column, I will discuss control measures for fireblight.

If you would like to see a video about fireblight that was produced by another MU Extension Horticulture Specialist, you can find it on the web at: http://vimeo.com/98732725