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Western Washington’s wet, mild spring is close to ideal for fungal and bacterial tree disease. Most of what we are called out to look at is not one dramatic infection but a pattern — the same tree losing leaves early every July, cankers reappearing on the same limbs, a conifer thinning from the inside out. Our ISA Certified Arborists diagnose the specific pathogen first, then tell you whether it can be treated, managed, or only planned around.
Free on-site diagnosis · We tell you when a disease is not treatable
Every disease has a different answer. Some are controllable on a schedule, some are only suppressed, and some have no chemical control at all.
Symptoms overlap heavily. Early leaf drop can be a leaf pathogen, a root pathogen, drought stress or girdling roots, and the treatment for each is completely different. We identify the cause before anything is applied.
For diseases with a known annual cycle — scab on apple and crabapple, anthracnose on dogwood and sycamore, needle cast on Douglas-fir — treatment works by being in place before infection, on timing tied to bud break and wet weather.
Pathogens that move inside the water-conducting tissue are reached by injection rather than by spray. This is the approach on high-value elms and on repeat-infection ornamentals.
For a large share of disease problems the most effective intervention is not chemical at all. Removing infected wood, opening the canopy so it dries faster, and correcting past bad cuts often does more than any spray — see tree pruning.
Open either list below. The first is what responds to treatment. The second is what does not — and we would rather you hear it from us before you spend money.
| Disease | Hosts here | How it is handled |
|---|---|---|
| Apple and crabapple scab | Apple, crabapple | Timed preventative program starting at bud break; sanitation of fallen leaves |
| Dogwood anthracnose | Flowering and native dogwood | Preventative treatment plus canopy pruning to reduce leaf wetness |
| Sycamore anthracnose | London plane, sycamore | Preventative treatment; removal of infected twigs |
| Swiss needle cast | Douglas-fir only | Treatment timed to needle emergence; not curable in one season |
| Bacterial blight and canker | Cherry, plum | Common west of the Cascades. Managed by dormant-season timing, pruning in dry weather, and copper-based treatment |
| Brown rot blossom blight | Cherry, plum, peach | More of a problem west of the Cascades. Treated on bloom timing |
| Pear trellis rust | Pear | Commonly reported on pear leaves in western Washington. Managed by timed treatment and removing nearby alternate hosts |
| Powdery mildew | Maple, oak, ornamentals | Rarely fatal. Treated where appearance or repeated defoliation matters |
| Tar spot | Bigleaf maple | Common on the Pacific Coast and cosmetic in most cases. Leaf clean-up is usually the only action needed |
| Verticillium wilt | Maple and others | No cure. Managed by pruning out affected limbs and reducing stress on the rest of the tree |
| Dutch elm disease | Elm | Preventative injection on high-value trees; prompt removal of infected wood |
Diagnosis drives everything on this table. We do not put a tree on a fungicide program without identifying what we are treating.
Three of the most damaging tree diseases in the Puget Sound region cannot be cured or controlled with any product, and any company telling you otherwise is selling you something that will not work.
Armillaria root rot and laminated root rot have no chemical control. Management is structural: assess whether the tree is still safe to stand, reduce other stresses, plan replacement with a species that resists the pathogen, and remove infected root material where practical.
Phytophthora root rot can be suppressed preventatively on trees that are not yet badly affected, but treatment does not kill an established infection. The real fix is drainage and planting depth.
When a root disease has compromised the structural roots the question stops being a health question and becomes a risk question. That is when an arborist report or a removal quote is the honest recommendation.
An ISA Certified Arborist inspects the tree on site. Photographs of the progression over previous seasons are genuinely useful if you have them.
We identify the pathogen, or rule disease out. A surprising number of ‘disease’ calls turn out to be root damage, buried root flares or drought stress from a dry August.
If it is treatable you get a program with timing. If it is not, you get told that, along with what management or removal would cost.
Disease treatment only works on the right calendar window. We schedule to the infection cycle, not to whenever the truck is free.
We check the response the following season and adjust. Most disease programs are multi-year, and we will tell you when a tree no longer needs to be on one.
You often cannot tell from symptoms alone, which is the whole reason diagnosis comes first. Early leaf drop, thin canopy and dieback are produced by disease, by drought, by root damage from construction, and by a root flare buried under too much soil or mulch. Treating the wrong one wastes the season.
Frequently, if it is caught before major canopy loss and if the disease is one that responds to treatment. Leaf and needle diseases are usually manageable. Root diseases such as Armillaria and laminated root rot have no chemical control, and in those cases the honest question is whether the tree is still structurally safe rather than whether it can be cured.
Almost always before symptoms appear. Preventative fungicide programs are timed to bud break and to wet-weather infection periods in spring, and dormant-season applications are used for cherry and plum canker. By the time leaves are visibly spotted in July, that season’s infection has already happened — treatment then is protecting next year.
Rarely. Most disease management is a multi-year program because the pathogen persists in the surrounding environment, in fallen leaves, or in infected wood. What changes year to year is how much intervention the tree still needs, and we will tell you when it can come off the program.
Many are host-specific — Swiss needle cast only affects Douglas-fir, pear trellis rust needs pear. Others spread readily between susceptible hosts on the same property, particularly the anthracnose group and bacterial canker of cherry and plum. Part of the inspection is identifying which of your other trees are actually at risk.
Wood chip mulch applied as a surface topdressing has not been shown to transmit tree pathogens, and Washington State University research supports using arborist chips this way. What matters is that chips are never dug in as backfill or a soil amendment around a new planting, and that infected root material from a root-rot tree is removed rather than chipped and spread back over the same area.
Sometimes. If a diseased tree has to come down, several jurisdictions want the condition documented, and insurers frequently ask for it after a failure. We write arborist reports for exactly this, starting at $400 for residential and right-of-way work. A report is not a permit and does not guarantee approval.
Treatment is quoted per tree after an on-site inspection — species, trunk diameter, the number of trees, and access all change the number. The consultation and the written quote are free.
Disease programs are usually multi-visit because timing matters more than volume, and the number of trees on the program drives the price more than anything else. If a diagnosis shows the tree is beyond treatment we quote removal instead. For seasonal care you can do yourself, our tree after-care guides cover maples, conifers, fruit trees and hedges.
Every certification number below links to that arborist’s credential record with the International Society of Arboriculture, so you can verify it before anyone sets foot on your property.
Washington L&I Contractor License PACIFA*813KG · WSDA Pesticide Applicator #109480 · $1M liability insured
Describe what you are seeing and when it started, and attach photos if you have them. An ISA Certified Arborist will inspect it and tell you plainly whether it is treatable.
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