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Press release

Frequently Asked Questions on Sudden Oak Death treatment

Q: How is this new treatment applied? Will it affect other trees nearby?

A: The phosphite compound, sold under the brand name Agri-Fos, is injected directly into the tree’s vascular system by a trained professional. When combined with an organosilicate, sold under the brand name Pentra-Bark, it can be applied topically to the bark of the tree.

Agri-Fos and the combination of Agri-Fos with Pentra-Bark are the only chemicals approved by the California Department of Pesticide Regulation for use to prevent or treat Sudden Oak Death infection.

Oak trees — coast live oak, Shreve’s oak, black oak and canyon live oak — can be treated by injection or bark application. Tanoaks can only be treated by injection.

Because the method of application is very targeted, the chances of the chemicals impacting the surrounding environment are very low.

Q: Which trees will be helped by this new treatment?

A: The treatment is only approved for use on oak and tanoak trees. There is no evidence that the chemicals are effective in other species of trees.

In addition, there is a range of susceptibility to the Sudden Oak Death pathogen within individual trees in the oak and tanoak species. For instance, the treatment may not help oak trees that are extremely susceptible to the pathogen.

The treatment is best used to prevent infection. However, it may be possible to prolong the life of an infected tree if it is treated quickly. The treatment should begin within 1-2 months of the first signs of an infection — usually viscous brown droplets on the intact bark of the tree. The treatment is not recommended for trees that have had symptoms for six months or longer.

Q: How can I tell how susceptible a tree is to Sudden Oak Death?

A: At present, there is no easy way to determine an individual tree’s susceptibility to infection by the Sudden Oak Death pathogen. Trees should thus be selected for preventive treatment based on the risk chart shown in Table 1 below. Treatment is only recommended for trees that fall within ratings 1 and 2 for risk.

Even then, trees with poor form or a spiral pattern of growth will often not respond to treatment. Injections have not been effective and are therefore not recommended for trees with decay pockets, punks or other malformations on the lower stem. Trees that are weakened by other diseases should not be treated.

Q: How long does it take for the treatment to work?

A: The treatments requires 3-6 weeks to be assimilated by the tree before it starts working.

Q: How can I get the treatment?

A: Agri-Fos and Pentra-Bark are sold through Agrichem, an Australian-based company with U.S. headquarters in Ohio. At present, the chemicals are only available to licensed professional pesticide applicators.

Training sessions will be made available to professional arborists through the UC Cooperative Extension in conjunction with Agrichem and the California Oak Mortality Task Force. For more details about the training program, contact Katie Palmieri at (916) 747-1924.


Table 1. Risk table for treatment of oak trees

Location Risk Rating by Tree Diameter
(1 = Most Severe Risk, 4 = Least Severe Risk)
Up to 10 cm Between 10-50 cm Greater than 50 cm
A 3 1 1
B 4 2 1
C 4 3 3
D 4 4 4

A: The oak or tanoak is

  • 30 meters or less from a California bay laurel tree known to be infected by P. ramorum
  • OR 50 meters or less downwind or downhill from an infected California bay laurel tree
  • OR 10 meters or less from an oak or any other tree known to be infected

B: The oak or tanoak is

  • 30 meters or less from any California bay laurel tree
  • OR 50 meters or less downwind or downhill from any California bay laurel tree
  • AND there are known infections within 300 meters in any known Sudden Oak Death pathogen host

C: The oak or tanoak is

  • 30 meters or less from any California bay laurel tree
  • OR 50 meters downwind or downhill from any California bay laurel tree
  • AND there are known infections within a 4-mile radius in any known Sudden Oak Death pathogen host

D: The oak or tanoak is in a region where there are no known infections within a 4-mile radius and there are no California bay laurel trees in the vicinity