This spring my blue oak tree’s leaves are changing to reddish brown and falling off. What is happening?

Both prolonged drought and a leaf disease called anthracnose (highly infectious during very wet years) can cause early leaf drop, especially in blue oaks, but also in other oak species. So, a single year of early leaf drop is almost never problematic.  Leaves should reemerge next year.  You may observe some die back of a […]

Is it okay to cover the base of a tree with extra soil?

The buttress or basal portion of a tree should never be covered by soil as this practice increases the chance that the tree will suffer from root pathogen attacks in the submerged part of the trunk. The soil should be removed until root flares at the base of the tree are clearly visible. Attacks by […]

In Marin County, recent rains led to foliar infections on Pacific madrone, denuding leaves. These plants now have healthy new growth. What happened?

Pacific madrone foliar infections associated with rains are common throughout the West Coast. Typically, the spotted and necrotic leaves are ultimately substituted with healthy foliage and the plant fully recovers.

How susceptible are canyon live oaks to Phytophthora ramorum?

Canyon live oak is an intermediate oak, meaning it is between the red and white oak groups. P. ramorum/SOD primarily infects only red oaks; however, it does also affect the intermediary canyon live oak.  In northern California (Humboldt County), canyon live oak infected with P. ramorum leads to dieback of large branches. In the Bay […]

How do I know if my area has been evaluated for sudden oak death?

If you live in a California county that is known to have sudden oak death (SOD), you can check to see if your area has been evaluated for the presence of the pathogen that causes SOD (Phytophthora ramorum) by downloading the free SODMAP Mobile app.  Doing so will allow you to see if trees have […]

My redwood has severe dieback and is near a coast live oak with SOD. Could the redwood have SOD?

Most likely the redwood is experiencing symptoms related to cycles between drought and rainy periods. However, if there is a significant presence of California bay laurels intermixed with redwoods, there may be enough pressure from the SOD pathogen to also cause problems on redwoods, both native and exotic. Any SOD oak infections are likely directly connected to […]

Other than for copper-based sprays, what control methods are available for cypress canker?

There are several  products that have been tested for controlling cypress canker. The following paper maybe the most useful one to compare products. Della Rocca, G., Di Lonardo, V., Danti, R. 2011. Newly-assessed fungicides for the control of cypress canker caused by Seiridium cardinale. Phytopathologia Mediterranea. 50 (1), pp. 65-73. The most effective active ingredients […]

If reforesting an area impacted by SOD with local acorns, what can be done to prevent spreading the pathogen during planting?

Take the following precautions when using local acorns for oak reforestation projects in areas impacted by SOD to help minimize pathogen spread. Place acorns in a 10% dilution of bleach for 10 minutes then rinse twice with tap water. Make sure volunteers’ shoes are free of soil, mud, and organic material. Be sure tools being […]

How do I clean my tools well enough to ensure I’m not spreading sudden oak death?

The most important part of ensuring that tools will not spread sudden oak death is to be sure that no organic debris or soil is present on the tool. This applies to all portions of the tool, including parts that may not be visible (like the return of a chain in a chainsaw or the […]

How often do you administer phosphonate to oaks to help protect them from sudden oak death?

Phosphonate injection treatments to help prevent sudden oak death infection of susceptible oak species (coast live oak; California black oak, Shreve’s oak, and canyon live oak), if applied in the fall (after October 30th ), need only to be applied once every other year (biannual frequency). If your first phosphonate treatment is in the spring, then […]

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