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 […]

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.

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 […]

Does rain affect preventative phosphite (e.g. Agri-Fos®) treatments for oaks?

When treating oak trees with phosphites to help prevent SOD, it may be beneficial to apply the topical treatment to bark that is dry.  Rain occurring after the treatment (even immediately after) does not affect the application. If injecting phosphites, it may be better to avoid rainy days, as lower evapotranspiration is often documented for […]

How long can Phytophthora ramorum survive in wood chip mulch?

Survival of P. ramorum (SOD pathogen) in wood chips depends on a few factors: Were the chips allowed to become wet? What size are the chips? Is green waste present? What time of year was the wood chipped? Where in California are the chips located? Chips that are piled wet or tarped and include infected […]

How long can Phytophthora ramorum survive in soil moved from an infested area?

Survival of P. ramorum (SOD pathogen) in dead hosts or non-plant substrates is extremely variable and strongly affected by climatic factors. Although a comprehensive study on this topic has not conducted, extrapolating from several studies we can say the following: Soil becomes more infectious from late winter to early summer in the presence of rainfall, […]

What can cause leaf tip scorch on redwood trees?

Leaf tip scorch symptoms on redwood trees are found from the lower to upper canopy and include healthy leaves interspersed with brown and grey leaves or portions of leaves. Grey leaves typically have black margins into the healthy tissue. Such symptoms are typically caused by a fungus called Pestalotiopsis funerea. They are commonly associated with […]

Bark beetles are attacking my oak. Will they kill the tree? What should I do?

Once bark beetles attack the main stem (trunk) of an oak, the tree is on its way out.  Insecticide treatments will not save it. Oak beetles are attracted to trees that are severely compromised.  They cannot attack healthy trees. The correct approach to avoid bark beetle infestations is not to apply insecticides, but rather to […]

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 […]

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 […]

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