Sudden Oak Death

What is Sudden Oak Death?

Sudden oak death, Phytophthora ramorum, is the common name for a disease that has killed hundreds of thousands of trees in California and Oregon.  Although it is called sudden oak death, Phytophthora ramorum attacks a wide variety of species, including stately Douglas firs and coastal redwoods.  Originally confined to dominant tanoak, coast live oak, and California black oak forests, sudden oak death has spread to horticultural nurseries and garden centers, making sudden oak death among the most significant diseases of this decade.

Treatment Strategy

Sudden oak death is a water mold, not a fungus, which means that common systemic and contact fungicides do not effectively control this disease. Agri-Fos® is the only researched treatment for sudden oak death with consistently positive results.  It is recommended to prevent the disease in areas where sudden oak death has been found, but does not cure already infected trees.

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Sudden Oak Death Treatment Option 1

Agri-Fos® is a bark sprayed product that requires the addition of a product called Pentrabark to help it move into the tree.  Treat by spraying the trunk as high as possible down to the base of the tree twice in the first year.  Apply once in November and again in May.  Follow up with annual treatments to maintain protection.

Agri-Fos® is only effective on tanoak and true oak tree species (i.e., coast live oak,California black oak, and Shreve oak).  Agri-Fos® has not been effective or has not been tested on other tree species, such as Pacific madrone or California bay laurel.  Agri-Fos® has not been tested on canyon live oak.

Application TypeBark Spray

DIY Equipment Product Needed:

• Agri-Fos®

• Pentrabark

• Hand pump sprayer with wand

Sudden Oak Death DIY Kit

Application Type – Bark Spray

DIY Equipment Product Needed:

• Agri-Fos®

• Pentrabark

• Hand pump sprayer with wand

How Is It Spread?

Phytophthora Ramorum Life Cycle Biology

Phytophthora ramorum is a fungus-like water mold, spread by wind and wind driven rain.  Tanoak leaves are infected first in the upper canopy.  Once there, if wet weather occurs, spores can travel to twigs in water films on the leaves, infecting them.  Once on the twigs, cankers form on tanoak and coast live oak trees.  It is these cankers that ultimately cause the death of the tree.

Susceptible Trees

Tree species confirmed to be infected include oaks: tanoak, coast live oak, and California black oak.  Other hosts include Douglas fir, rhododendron, redwood, Pacific yew, evergreen huckleberry, bigleaf maple, several varieties of fern, California buckeye, California coffeeberry, cascara, toyon, honeysuckle, wood rose, western starflower, and California bay laurel.


Symptoms of sudden oak death vary among affected species.  Some suffer tip and shoot blight, which can be fatal, while in other species sudden oak death causes leaf blotches, which are primarily aesthetic.  In oak trees, sudden oak death causes bleeding cankers that girdle trunks, inviting secondary pests, such as Hypoxolon canker.  In other species – such as rhododendron and Douglas fir – leaf blight and shoot blight symptoms are seen.  Consequently, the disease is called P. ramorum shoot blight when infecting these trees.  Regardless of species, leaf spots are often visible, occurring where water collects on the leaves, especially on tender new foliage.


Spring and Fall



Risk of Spreading


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