Are there any treatments available for an oak with Armillaria (oak root fungus)?

Once an oak has the oak root fungus Armillaria (often due to excessive watering),  most treatments will be ineffective. Be sure the base of the tree is free of mulch and other organic debris and slightly expose the root system at the root collar. While fertilizing may not help, try using one bark application of Agri-Fos + PentraBark. This application provides minimum nutrients, but strengthens the defense mechanisms of the tree. Of course, stop watering unless absolutely necessary. Water should never be administered from July-September.

My pear tree was looking great. Within a week one of the limbs died and now it looks like the whole tree is dying.

It sounds like your tree is having problems providing enough water to the canopy to keep the foliage and cambium alive. If you are not watering it, that may be the problem. If you are watering it, your tree may have contracted a root disease. In that case, it is important to clear all organic material at least 3 feet around the stem, slightly expose the root system next to the stump to the air, avoid fertilizers, and water minimally.

I have an oak tree that is leaking a dark substance 4′ up the trunk, but otherwise it looks healthy. I live in Alameda County. Do I need to be worried about sudden oak death?

Download sod map mobile and tap the risk button. If the risk shows up as high or moderate, call an arborist listed at http://www.suddenoakdeath.org/diagnosis-and-management/arborists-applicators/. If you get an insufficient data response, then see if you have any CA bay laurel trees within 20 yards of the oak. If you find any, do they have possible P. ramorum (pathogen that causes sudden oak death) symptoms (symptomatic photos: http://www.suddenoakdeath.org/library/photos/plant-symptom-photos/; host information: http://www.suddenoakdeath.org/diagnosis-and-management/hosts-and-symptoms/). If you do find questionable symptoms on bay, again, call an arborist listed at http://www.suddenoakdeath.org/diagnosis-and-management/arborists-applicators/ for a site visit.


Can coast live oak be used in a large-scale Bay Area tree planting project without exacerbating SOD?

My organization is considering launching a large-scale urban tree planting project in the Bay Area, with the goal of adding one million trees to the urban forest inventory within 15 years. We are interested in coast live oak (CLO) as a major component of the effort for a number of reasons, including the ease with which seed can be collected and planted, drought tolerance, habitat value, high potential for carbon sequestration and rainfall interception, and status as a “signature tree” of the local landscape.

The plan is to gather seed locally from many locations, and plant with minimal site preparation and no supplemental irrigation or other artificial life support systems. Trees will be monitored and cared for over time, and replanting will take place as needed to ensure that we continue to make progress toward our goal. Obviously we don’t want to exacerbate the sudden oak death problem. Our hope is that, on the contrary, widespread and large-scale planting with subsequent monitoring might help identify resistant trees. What recommendations do you have?

First of all, this is a really neat project and you are absolutely correct about the benefits of planting CLO. Based on the information provided, the following are recommendations for the project:

In addition to coast live oak, it would also be good to plant Oregon white oak in the northern greater Bay Area, valley oak in the middle portion of the Bay Area, and blue oak in the southern part of the Bay Area. The rationale for this is that diversity/biodiversity is always good and the three alternate oak species are immune to SOD. A good overall planting ratio would be 75% CLO and 25% other species.

The big issue is going to be when California bay laurel is present, as it helps to spread Phytophthora ramorum. CLO should never be planted within 20-25 yards of bay for this reason. Unfortunately, bay has become invasive and SOD is actually increasing its abundance, so where bay is at least 10% of the stand, plant the other oak species recommended above. In riparian areas, bay should be left untouched.

If the stump of a felled tree is left in place, can the roots to continue to grow?

A lot depends on when the tree is felled. If a tree is cut in winter, it is possible that the root system will experience an additional year of growth. What happens to the root system depends on many variables, including soil type and presence of other trees of the same species adjacent to the one being felled. If the same species is present and the root systems of neighboring trees are grafted, the roots may be kept alive by trees still standing.  Some species, like aspen, will actually sprout new shoots along the root system. Often a stump with roots that are alive will seal the cambium on the stump surface, resulting in a round bump along the entire circumference of the tree right over the cambial area (i.e. just inside the bark).



We have bays 100 feet downwind from a coast live oak that seems to be dying of SOD. How do we have our oak tested and how do we determine if the bays are carriers?

Oak testing is routinely done by arborists. It is a rather involved and tedious process that requires a fair amount of finesse and know how as it entails wounding the tree by shaving off the outer layer of bark to collect infected tissue. If you decide to have your oaks tested for SOD, consider going to the Trained Professionals List for arborists that have recently attended an official SOD seminar (Not intended to be a list of recommended professionals, this list does serve as an additional filter when trying to identify arborists that are up-to-date on the latest science-based SOD information.).

Alternatively, a less invasive method of determining the presence or absence of SOD on your property is to sample symptomatic bay leaves (See Hosts and Symptoms for SOD symptoms.). Keep in mind that any infested bay in the general vicinity (typically within 200 ft of an infected oak) may be the inoculum source for infection of your coast live oak. If bay sampling is your preferred method for pathogen detection, you can call your local UC Cooperative Extension office to find out if the California Department of Food and Agriculture is processing leaves from your county and, if so, what the protocol is for sample submissions. In lieu of submitting samples through your county, you can go to www.sodblitz.org to find out when a SOD Blitz will be held in your region (Dates for each year are posted by January 30th. Blitzes typically occur from March to June). Attending a blitz will afford you the opportunity to learn more about SOD, including the latest disease control strategies, during a 1-hour training session. At the end of the session you will be given all sampling materials and instructions for submissions. Blitz participants are free to submit as many leaves as necessary, meaning that you can send in all suspicious leaves from your property as well as from the neighborhood or nearby local parks. All leaves are processed at UC Berkeley and all sampling results are published in a database available at www.sodmap.org or through the free App SODmap mobile.

Armillaria is slowly killing my Thuja hedge. What is a comparable replacement hedge that will give me the same amount of privacy and be resistant to this fungus?

The first question to ask is what type of irrigation is being used currently on the hedge. Most landscape oak root fungus problems are due to overwatering in summer months. However, Thuja orientalis (=Platycladus orientalis) is quite susceptible to Armillaria even without heavy irrigation as highly susceptible species do not require excessively high soil moisture to be killed.

Prior to any new planting, as much of the old hedge (including roots) should be removed. In addition, any other decaying wood should be removed. Replanting with plants that do not require supplemental watering is best. Some CA natives that make good hedges include: ceanothus, island mountain mahogany, manzanita, and toyon. Non-native possibilities include Leyland cypress and Japanese privet. Keep in mind though that even plant species listed as resistant to oak root fungus will die if overwatered.

Is it okay to prune coast live oaks in the winter if there is no SOD inoculum in the area? Are there other pests that are active in the winter that are of concern?

Although there may be few insects flying in the winter, the wet winter season (actually fall through spring) is a prime time for production of fruiting bodies by many wood decay fungi. The combination of fresh pruning wounds (especially large wounds), high spore densities of wood decay fungi, and moist conditions (favoring spore germination) can favor new infections by these fungi. From the standpoint of reducing risk of infection by wood decay fungi, pruning in late spring or early summer is probably preferable.

In general, pruning live branches from mature oaks should be kept to a minimum. However, if it is necessary to prune coast live oak branches, as long as they are less than 4″ in diameter, the presence of SOD is not a concern. Though, it is important to prune the oak correctly.

• Make sure you prune right where the tapering of the branch ends from the main stem or even slightly closer to the stem (1/2 in. from the end of the tapering towards the stem).

• Make sure the cut is clean and allows for water to drip without accumulating.

After taking down a P. ramorum-infested bay tree, can the foliage be left onsite to decompose?

Once down, spores from bay foliage will not travel nearly as far as they do in the canopy. The concern on the ground is that infested leaves, while still fresh, could have spores picked up during a wet event from soil splash onto the trunk of the tree. So, spread bay foliage in a thin layer in a sunny area that will promote drying. Be sure to not have foliage near the base of oak or tanoak trunks where soil splash/infection could occur.