Twig blights and cankers
Twig blights and cankers are general terms for a condition where the sapwood
of a twig or a shoot (twig blight) or a larger limb, branch or trunk (canker)
has been killed. Twig blights and cankers are caused by a variety of fungal organisms
and a few bacterial ones in either a secondary or primary manner.
Most organisms that cause twig blights and cankers are opportunistic pathogens.
They are secondary; invading and infecting tissue only after it has first been
stressed or injured by other organisms or conditions. Twig blights and cankers
are commonly observed after late spring freezes, on recent transplants, on declining
trees and shrubs, and on plants placed on unsuitable sites. Cankers at the base
of trunks of trees and shrubs are common after injury by string trimmers.
Pathogens that cause twig blights and cankers in a primary manner are able
to invade healthy, uninjured tissue. Diseases such as fire blight, Sphaeropsis
tip blight and sycamore anthracnose are examples of twig blight and canker inducing
diseases caused by primary pathogens.
Primary hosts
in Missouri
No host is immune to twig blights and cankers caused by opportunistic pathogens
that invade stressed or damaged tissue. Certain hosts are susceptible to primary
pathogens that cause twig blights and cankers.
Symptoms
and diagnosis
Figure
1
A canker caused by Cytospora sp. on a small tree limb. The black spots
with in the canker are the fruiting structures of the fungus.
Sunken, discolored or different textured tissue from surrounding areas may
indicate a canker. See
figure 1. Sometimes cankered areas have abundant resin or sap flow. Often
if this area is viewed closely, fungal structures may be observed. The exact fungal
identity often depends upon microscopic observation.
Integrated
management strategies
There are no chemical controls for twig blights and cankers caused by opportunistic
pathogens. These are managed by keeping the plant in vigorous condition. Affected
areas should be pruning out whenever possible. Diseases such as fire blight, Sphaeropsis
tip blight and sycamore anthracnose, which are caused by primary pathogens, sometimes
may be managed by using appropriate cultural and/or chemical methods. The presence
of twig blights does not necessarily indicate a serious problem. Some hosts such
as river birch and willow are prone to twig blights even when vigorous. If a host
is growing well and not unduly disfigured these should not be cause for concern.
Updated 6/9/09