Brown leaves often remain attached to branches
even after tree mortality (Source)The common name "Sudden Oak Death" may be misleading due to both
the words "sudden" and "oak". The common name was given
because of the apparent rapid decline in crowns of infected oak trees,
changing
from green to brown in sometimes a matter of just a few weeks. But researchers
do not yet know how long the disease actually progresses before death.
Also,
many infected hosts do not decline "suddenly", or even die at all.
The disease seems to manifest itself and progress differently depending
on
many factors including individual tree characteristics, site factors and
the species.
The term "oak" in Sudden Oak Death may be misleading because it
does not reflect the potential that this disease has for causing serious problems
in a wide variety of potential non-oak hosts.
SOD not only causes severe cankering and rapid death of oaks, but has been
found causing foliar and twig blights on numerous other trees and shrubs.
There are at least 14 different species of ligneous hosts known to be affected
by P. ramorum (for current list, see hosts).
Many of these hosts, such as those in the genera Quercus,
Arbutus, Acer,
and Rhododendron have valuable counterparts
in native and planted Texas landscapes.
Sudden Oak Death (SOD) is a newly discovered, highly infectious
disease caused by a fungus-like organism within the genus Phytophthora.
The
disease was first discovered in Northern California in 1995 where it has
since been implicated in large-scale oak mortality. It is estimated that
tens of
thousands of tan oaks, coast live oaks and black oaks have been killed on
the west coast so far.
The pathogen was isolated and identified in 2000 by researchers from the
University of California as Phytophthora ramorum.
This is an organism that has previously only been known to exist in Germany
and the Netherlands, where it was found infecting Rhododendrons and Viburnums.
There are many aspects of SOD that are poorly understood
For example, the origin of the California outbreak disease is still unknown.
There is no information on how long the disease has been on the West Coast,
but there is some speculation that it may have been there for quite awhile
and the damage is just now escalating due to the accordance of predisposing
stress. Changes in environmental conditions such as climatic change, fire
suppression, and alterations in land use patterns have all been implicated
in the epidemic.
Sudden Oak Death is changing the ecology
of some of California's landscapes (Source)
The array of symptoms observed on different hosts currently
cannot be explained and there is an unaccountable variable mortality rate
among infected plants.There is also some speculation that it originated in
Europe and perhaps transported on infected rhododendrons, but there is
no
direct evidence yet to support this claim. So far, there is no 'cure' yet
for SOD, although research is being conducted in this area.
Although SOD has not yet been identified in the United
States outside of California and Oregon, laboratory studies have shown that
many species outside the current distribution are potential hosts, including
eastern and northern red oak, and pin oaks. The spread of Sudden Oak Death
to other parts of the country must be considered, given that the pathogen
can be moved great distances by transport in nursery stock such as SOD infected
rhododendrons, or in soil and bark products.
For technical assistance with this page contact the Technology Assisted Learning Lab at (979) 862-3449 or via e-mail at prabha@neo.tamu.edu. For more information about Sudden Oak Death at Texas A & M University, contact Dr. David Appel at 979-845-8273 or by e-mail at appel@ppserver.tamu.edu; or Sara Service at 979-587-2701 or by e-mail s-service@neo.tamu.edu