P&PDL Picture of the Week for
November 29, 2004

When a major storm strikes...

Gail Ruhl, Senior Plant Disease Diagnostician, Interim P&PDL Director, Purdue University

When a storm strikes, some trees seem to be able to come through with only minor damage, while others suffer the loss of large limbs or sizable parts of their branching structure.

This willow tree (what’s left of it) lost several large branches during the windy, snowy weather last week. Located beneath utility lines, this tree has been repeatedly topped over the years. According to Dr. Alex Shigo, topping is the most serious injury one can inflict upon a tree.  Topping opens the tree up to an invasion of rotting organisms. Severe topping and repeat topping can set up internal columns of rotten wood. Rotted individual limbs, or the entire tree, may fail, often years later in conjunction with environmental stress factors such as excessive winds, ice storms and heavy snow. Usually a conk (see image below) or mushroom "fruiting" body is the first sign of infection.

Prevention: All deciduous trees can get heart rot. Heart rot fungi, however, do not invade living wood of healthy trees. Thus, as long as a tree is growing vigorously, rot will be confined to a small central core. This is called compartmentalization. If the tree is weakened and fresh wood exposed by severe pruning or storm damage, decay fungi can advance to more and more wood.

Control: Minimize pruning wounds that expose large areas of wood. Carefully remove broken branch stubs following storm damage. Have suspect heart rot trees checked by a certified arborist to determine if sufficient live wood is present for structural safety. Check trees every few years to be certain new growth is maintaining sound structure. Large trunks and main branches with extensive decay may have little sound wood to support the tree and may cause damage to surrounding buildings or, as in the case of this willow, power lines and nearby fence.

For more information on topping please see Don't Destroy Your Large Trees by Topping

Also check out Why Hire an Arborist? (pdf file) - Down the Garden Path Newsletter, March 1998

Click on image to enlarge

Rotted branch on fence

Internal rot of limb

Tree in power lines

Fungal conk

Wood rot on trunk

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service