Draft: 3/01/02

To supplement tree retention guidelines

Damage caused by pitch canker results first from the death of individual branch tips.  Over time, larger branches and even the main stem of the tree can also become infected.  At these later stages of disease development, little can be done to influence progress of the disease.  However, while symptoms remain restricted to branch tips, it is possible to remove the infected parts through pruning. 

The death of branch tips is caused by growth of the pitch canker pathogen, which girdles the branch and cuts off the flow of water and nutrients.  Although this results in death of the branch distal to the infection (i.e., between the infection site and the tip of the branch), below this point (i.e. closer to the trunk of the tree), the branch is unaffected.  Consequently, if the branch is removed by cutting it below the junction of living and dead needles, the pitch canker infection on that branch can be eliminated.  If a tree has a very small number of infected branches, it may be practicable to remove all of them.  If so, such a tree can be rendered disease-free, at least temporarily.  Unfortunately, in an area where pitch canker is well established (i.e., many trees are infected), it is likely that a tree with symptomatic branches also has infections that are not yet visible.  As a result, removal of branches showing symptoms is not likely to rid the tree of all active infections.  For this reason, several rounds of pruning may be necessary to remove all infections.  Even this may not be sufficient in areas where the disease is well established because new infections can continue to occur.  Consequently, there is no guarantee that attempts to rid a tree of pitch canker by pruning out infected branches will prove to be successful.

            Notwithstanding the above limitations, removal of infected branches may be worthwhile under some circumstances.  In areas where pitch canker is not common, it is possible that inoculum levels are low and new infections will not occur at a high rate.  In this case, pruning may actually slow the rate at which the disease develops in a tree.  Although new infections are likely to occur, pruning might succeed in extending the useful life of a tree.  If aesthetic considerations are of primary importance, such that removal of unsightly branches will allow a tree to be retained in the landscape, then the cost of pruning may be offset by a delay in removal and replacement of the tree.