I get calls from people who are concerned about the health of valued, older trees. Sometimes it is a plea for advice to save a declining tree. And sometimes they feel certain it is done for and they need an authoritative opinion, the equivalent of a death certificate.
These are treacherous waters for tree owners and experienced arborists. One example occurred long ago. Someone asked if their redwood tree had died. As it turned out, it was a dawn redwood (Metasequoia). The species is closely related to the evergreen coast redwood but it is deciduous. In winter, it looks like a dead redwood.
Another incident involved a large specimen, transplanted olive tree. One of several in a landscape, it had dropped all of its leaves while the others were vigorous. Probing revealed saturated soil where runoff from an adjacent irrigated landscape, upslope, was collecting in the root zone.
After some earthwork to divert the excess water, the root zone dried out. The tree looked virtually dead all summer. Then in September, when the owner had called the crane service to pull the tree, new leaves began to sprout from the limbs. A living tree was saved, and the landscape contractor was saved from paying thousands of dollars for a replacement under contract terms.
Two more examples: One was a large eucalyptus—a broadleaf evergreen- that dropped all of its leaves one spring. A close look at the fallen leaves revealed signs of a foliar disease, yet the trunk and branches appeared healthy. I advised irrigating the tree and waiting. It leafed out in good health later that summer. And the owner praised me almost as a miracle worker.
This happened again with another huge eucalyptus. Except this time, I poked and prodded and found no signs of life in the tree. I recommended removal. I was glad the owner ignored my advice. The following spring, the tree leafed out and still stands, healthy as ever.
Eucalyptus are tricky!
The native oaks are a bit easier to work with. One recent example was a coast live oak that had been subjected to flooding from a landscape water leak. All of the leaves were dead, the trunk was covered with fine, tan powder (the frass from ambrosia beetle infestation), and even though there was still a bit of green tissue in the branches, light excavation of the root collar – the base of the trunk — showed all dead brown tissue. To me, that is conclusive. The tree is a goner.
Here is one that happened this year and it is a common concern. A property owner was worried about a large old blue oak, which was looking nearly dead. Even though many leaves had died and fallen in late summer, a close look revealed the remaining leaves had varying degrees of dead patches caused by anthracnose — a group of fungal diseases — and lower leaf surfaces covered with powdery mildew. The good news is the twigs were generally supple, with bright green inner tissue and the buds were plump and ready for sprouting next spring.
My take on this disease problem is that the past two years have brought more spring moisture, and humidity than our native oaks are adapted to. Conditions favor the diseases. We have been seeing a terrible outbreak, notably with powdery mildew on blue oaks in the Montecito area in Napa.
Blue oaks (Quercus douglasii), which are dominant in the high and relatively dry areas in Napa County, have this ability to survive with a brief period of growth in spring and early summer. They often drop their leaves in late summer. It is an adaptation for avoiding drought stress. And, hopefully, a way to shed disease and recover when conditions favor the trees.
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