Quick answer: Cypress Canker in Cayucos — The tree that thrives here is the one chosen for this coast: fog, salt, wind and shallow soil are the local constraints, and mature size is the constraint most often ignored. Planting is a matter of putting the right species in a site that can hold it, then keeping the root flare visible and the first summers watered.
Field note. What we see is that the coast is forgiving to the right species and unforgiving to the wrong one: the same tree that looks comfortable four streets in will burn on the windward side of a Cambria lot.
On the other hand, natives are not automatically the answer at every address — a species that belongs in the watershed can still be the wrong size for the garden it is standing in.
On the cypress that face the water in Cayucos, dieback usually starts on one side. A few branches go dull, then straw, while the rest of the tree keeps its colour. It looks like wind burn, and for a season or two it is easy to believe that is all it is. Then the dead patch widens toward the trunk and the tree’s shape begins to lean out of the wind.
The fungus behind it
Cypress canker is caused by Seiridium species, which enter through bark wounds and grow in the cambium, killing the tissue in a band that girdles the branch from the inside. The first external sign is often a slight swelling or a dark streak on the bark, well before the foliage turns.
What makes it so effective in a garden is that the wounds it needs are the ones people make. Hedge shears, a ladder scraped against a trunk, a string trimmer at the base — every one is a door. A sheared cypress hedge on this coast is a canker nursery, and the damage is cumulative in a way that is invisible until the hedge goes brown in patches.
Why topping makes it worse
A topped cypress cannot regrow from the cut. The stubs die back, and each stub is an open wound at the top of the tree where rain and salt sit. Canker moves into those stubs and down. Trees that have been hard-pruned into a shape are consistently the ones that fail first in a wind event, because the structural wood that held the crown has been replaced by a shell of dead stubs.
If a cypress has outgrown its space, the honest options are removal and replanting, or a considered reduction that takes no more than a quarter of the live crown in a single year, cut back to side branches rather than to stubs. The second option costs more and takes longer, and it is the only one that leaves a tree.
The hedge is a special case
Cypress planted as a screen is a different problem from cypress planted as a specimen. A hedge is cut on a schedule, every cut face is a wound, and the density that makes it a good screen also holds moisture against the bark through the fog months. Once canker is inside a hedge it moves along the row, because the trees are close enough for rain splash and shared tools to carry it.
The usual result is a hedge that goes brown in one section, is cut back hard, goes brown in the next section, and is eventually replaced. Replacing it with the same species in the same place tends to produce the same outcome, which is why the more durable screens on this coast are mixed — a cypress for height, something else for the lower band.
Telling canker from root disease
Both look like dieback from the top, and they call for opposite responses. Canker kills in one direction along a branch; root disease kills the whole crown at once and usually shows as a thinning that begins across the entire tree rather than on one side. If the soil at the base stays wet, if the tree sits in a lawn or below a downspout, suspect the roots first.
A quick test: peel a strip of bark from a recently dead branch. Canker shows as a brown or reddish stain in the wood under the bark, running lengthwise. Root disease shows as dark, soft tissue at the base of the trunk instead.
What to do with an infected tree
Remove the affected limbs back into clean wood, sterilise the saw between every cut with alcohol, and dispose of the cuttings away from other cypress. Do not chip them onto the same property. Then leave the tree alone for a season and watch the boundary.
Where the canker has reached the main stem, or where the tree leans over a structure with a compromised base, the decision is no longer horticultural. That is a risk assessment and, if the finding is bad, a hazardous removal. On a bluff lot the arithmetic gets simpler than people expect: a cypress is replaceable, a roof is not.