Sequoia sempervirens, the coastal redwood, is one of the most beloved and successful trees in landscapes in the Napa area in terms of beauty, rapid growth and resistance to pests, diseases and decay. Perhaps it is too successful, considering its monumental size.
All too often, I see them out-growing the limited space in suburban gardens, their trunks and buttress root mounds lifting walkways and other infrastructure and their roots invading drain lines.
Those are instances of — call it what you prefer — wishful thinking or just plain bad planning.
Redwoods almost always thrive here as long as they have moisture, good drainage, sunlight, and decent soil.
Occasionally they have individual whole branches or tops that die as a result of redwood canker, an opportunistic fungal infection typically resulting from drought stress.
A recent case raised another redwood health issue. The owner was concerned because one redwood in a close grouping of good size trees looked like it was dying.
He thought it might be Sudden Oak Death (SOD). Yes, they can be infected, but they do not die of it. In redwoods it only infects needles and mostly in the lower canopies.
This tree had dead needles throughout the canopy, right up to the top. On close inspection, it became clear that the affected branches were still alive and the adjacent redwoods in the grove all showed varying degrees of the same symptoms. The needles showed brown and gray tip dieback that tended to be fairly uniform on any given branchlet. SOD symptoms in coast redwoods are reddish brown dead whole needles irregularly scattered on branchlets.
The symptoms just did not fit. In addition, I knew that the SOD mapping effort shows no cases of SOD near this site. Infection requires a foliar host, typically California bay laurel within about 60 feet. Later, checking the SOD map (see: https://nature.berkeley.edu/matteolab/?page_id=4262) I found the site and measured the distance to the nearest confirmed SOD find. It is .92 miles away.
Ruling out SOD, I turned to a more obvious and likely cause: Salt burn. Coast redwoods are susceptible and the region where this site is located is notorious for bad well water, in particular, high concentrations of boron. In addition to that our conversation led to the fact that the septic tank, located adjacent to the worst-affected tree, was ruptured.
Making things worse, the site sits low in the neighborhood and drainage is poor.
In June 2015, during a one-day seminar on trees, drought and using water wisely, arborist Nelda Matheny had spoken on the subject of recycled water for landscaping.
I spoke with her that day and she mentioned that the quality of Napa’s recycled water is good and actually better than the well water in Coombsville, the region I’m discussing here.
The trees on this site had not been irrigated with recycled water so the most probable cause boiled down to salt toxicity.
The trees could be absorbing excessive boron from groundwater and, probably, household chemicals such a sodium and chlorides.
Until soil, water and tree tissue analysis are done, a good starting point is to repair the septic tank, improve site drainage if possible and try to leach excess salts from the root zone with good quality water.
Abundant rainfall could help as long as drainage is good.
The next alternative, assuming the well water is too high in boron, would be to buy potable water, store it on site and use it to flush salts out of the root zone.
Come and join the Napa branch of the 2019 Sudden Oak Death Blitz. It starts Friday, April 26, at 6:30 p.m. at the UC Extension classroom, 1710 Soscol Ave.
It is a collaboration of the UC Berkeley Forest Pathology Lab and volunteers to search for the disease in local bay laurel tree leaves, collect samples and submit them to the lab for analysis and mapping.
First, there is a brief informational session. Participants then have the option to go out and collect samples on Saturday and Sunday and return them to the classroom where they will be picked up and and taken to the Berkeley lab for analysis.
Results are posted on the Lab’s website in October.
It is fun, educational, and provides volunteers with the opportunity to take part in a concerted effort to map and manage Sudden Oak Death.
The event is free, and there is no advance registration.