The Short Answer
Six problems cause most of the tree disease calls we run in the Sacramento area: anthracnose in sycamores, London planes, and Modesto ash; Armillaria (oak root fungus) in native oaks; fire blight in pears and other rose-family trees; broadleaf mistletoe; aphid and scale honeydew; and bark beetles in drought-stressed pines and redwoods. Most are manageable if caught early. The pattern to watch for is decline that repeats or worsens each year — dieback in the same part of the crown, mushrooms at the base, bark coming loose, or a canopy that thins while the neighbors' trees stay full. When you see that pattern, a tree health assessment beats guessing.
Anthracnose: The Spring Leaf Drop in Sycamores and Ash
Anthracnose is a group of fungal diseases that hit Sacramento hard in wet springs. Sycamores, London planes, and Modesto ash are the main victims — the fungus kills new leaves and twigs as they emerge, and by May the tree can look half-dead.
If your sycamore or ash gets hammered every spring, the long-term fix is structural: reduce the fungus load with sanitation pruning and improve airflow, rather than trying to protect every leaf. A tree that also shows major deadwood should be assessed before the next windstorm.
- What it looks like: brown, blotchy dead areas along leaf veins, distorted or curled new leaves, heavy leaf drop in April and May, and dead twigs at branch tips. London planes in Midtown and East Sac often drop so many leaves it looks like autumn in spring.
- Why it happens here: the fungus thrives when spring stays cool and wet during leaf-out. Dry springs mean light anthracnose years; a rainy March and April mean a bad one.
- The good news: established trees almost always releaf by June. A single bad year is cosmetic.
- The real risk: repeated defoliation year after year drains the tree's energy reserves, and the accumulating twig dieback creates deadwood that breaks in the Delta breeze and winter storms.
- Management: prune out dead twigs and branches during the dry season, thin the canopy for airflow so leaves dry faster, rake and remove fallen leaves that harbor the fungus, and keep the tree vigorous with proper summer watering.
Armillaria: Oak Root Fungus in Native Oaks
Armillaria mellea — oak root fungus — is the most serious disease on this list because it kills the roots that hold the tree up. It is native to our area and lives in the root systems of valley oaks, interior live oaks, and blue oaks, often for decades before symptoms show.
If you see mushrooms at the base of a mature oak — especially one with a lawn or irrigated bed planted over its roots — do not just kick them over and move on. Get the tree assessed. Native oaks are protected in the City of Sacramento and in unincorporated Sacramento County, so if removal turns out to be warranted, the assessment documentation also supports the permit application.
- What it looks like: clusters of honey-colored mushrooms at the base of the trunk in fall and winter, white fan-shaped fungal mats under the bark near the soil line, thinning canopy, undersized leaves, and branch dieback that spreads over several seasons.
- The trigger: summer irrigation against the trunk. Native oaks evolved with bone-dry summers; lawns, drip lines, and raised planters around the root crown keep the base wet in July and give Armillaria exactly the conditions it needs.
- There is no cure. Management means keeping water and soil off the root crown, not trenching or compacting the root zone, and monitoring the tree's stability.
- The safety question: an Armillaria-infected oak can look reasonably green up top while its anchoring roots rot. Root failure is how large oaks end up flat on houses without warning.
Fire Blight in Pears, Apples, and Ornamental Plums
Fire blight is a bacterial disease of rose-family trees — ornamental and fruiting pears, apples, quince, pyracantha, and hawthorn. It spreads fast in warm, wet spring weather during bloom, and the name describes the result: branches that look scorched by fire.
Caught early, fire blight is a pruning problem. Ignored for a few seasons, it can move from branch tips into main scaffolds and kill the tree. If more than a few branches show strikes, have the tree evaluated before cutting — the pruning strategy matters as much as the pruning itself.
- What it looks like: blossoms and new shoots suddenly wilt and turn black or dark brown, dead leaves stay attached instead of dropping, and branch tips curl over into the classic shepherd's-crook shape.
- Where we see it: flowering pear street trees all over Elk Grove, Natomas, and newer Roseville subdivisions, plus backyard apples and pears throughout the region.
- How it spreads: bacteria enter through blossoms and fresh cuts, moved by rain splash, insects, and dirty pruning tools. Pruning an infected tree and then a healthy one with the same unsanitized saw spreads it efficiently.
- Management: cut infected branches back well below the visible damage into clean wood, disinfect tools between every cut, and do removal pruning in dry weather. Avoid heavy nitrogen fertilizer, which pushes the succulent growth the bacteria prefer.
Broadleaf Mistletoe: The Green Balls in Winter Canopies
Drive through Carmichael, Fair Oaks, or older Sacramento neighborhoods in January and you will see them: dense green balls hanging in bare Modesto ash, silver maple, and oak canopies. That is broadleaf mistletoe — a parasitic plant, not a fungus, and it is stealing water and nutrients from the branch it grew into.
- How it spreads: birds eat the sticky white berries and deposit seeds on branches, where the seedling drives root-like structures directly into the wood.
- Why it matters: a few clumps on a vigorous tree are tolerable. Heavy infestations stress the tree, kill branches beyond the attachment points, and add weight and wind resistance exactly where limbs are weakest.
- Why pulling it off fails: the embedded roots resprout. The visible clump is only the top of the plant.
- Effective control: prune infested limbs at least a foot or more below the attachment point, back to a proper lateral. On heavily infested trees where that would gut the canopy, cutting mistletoe flush and monitoring regrowth is the compromise.
- Timing: winter is ideal — the mistletoe is easy to spot in a bare canopy, and dormant-season pruning suits most host species. Native oaks should be pruned in the dry season regardless.
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Aphids, Scale, and the Honeydew Mess
Sticky pavement, shiny leaves, a black film on the fence — that is honeydew, the sugar excreted by aphids and soft scale feeding in the canopy. In Sacramento the biggest offenders are hackberry, tulip tree, crape myrtle (the crape myrtle bark scale has spread through the region), and ornamental plums.
We deliberately avoid prescribing sprays or systemic products in an article — the right call depends on the species, the pest, nearby pollinators, and current regulations. A tree health assessment identifies the actual insect and gives you options that fit your situation.
- What it looks like: sticky drip under the tree, sooty mold turning honeydew-coated surfaces black, curled leaves, and ants trailing up the trunk — ants farm the aphids and defend them from natural predators.
- Damage level: mostly cosmetic on a healthy mature tree. The mold blocks some sunlight and the mess is real, but honeydew insects rarely kill established trees.
- When it signals bigger trouble: infestations that get dramatically worse each year often point to a stressed tree — poor watering, compacted soil, or root problems that weaken its natural defenses.
- Management: control the ants, support natural predators like lady beetles and lacewings, hose off small trees, and fix the underlying stress. Heavy or recurring infestations are worth a professional look before you spend money treating symptoms.
Bark Beetles in Stressed Pines and Conifers
Bark beetles rarely attack healthy trees. They attack stressed ones — and after Sacramento's hot, dry summers, there are plenty. Drought-weakened Monterey pines, ponderosa pines in the foothills, and the coast redwoods planted across 1970s–80s suburbs are the usual targets.
- What it looks like: fading foliage that goes yellow, then rust-red, from the top down or in whole sections; small round exit holes in the bark; popcorn-like pitch tubes on pines; and fine reddish boring dust in bark crevices and around the base.
- The hard truth: by the time a pine turns red, the beetles have usually already done their work and moved on. There is no rescuing a successfully attacked tree.
- Prevention is watering: deep, infrequent summer irrigation is the single best beetle defense for landscape conifers. A vigorous tree drowns attacking beetles in pitch; a drought-stressed one cannot.
- Remove dead trees promptly: a beetle-killed pine is both a brood source for attacks on neighboring trees and a fast-developing hazard, since dead pines get brittle within a couple of seasons.
- Foothill note: in Auburn, Placerville, and Pollock Pines, standing dead conifers are also a fire fuel problem under defensible space rules — see PRC 4291 guidance at readyforwildfire.org.
The same crew from estimate to cleanup.
No juggling separate contractors for one tree. Tell us the address and what you're dealing with, and we'll come back with a written, site-specific number.
- Removal, trimming, stumps, and cleanup handled by one crew
- Free, site-specific estimates — priced to your tree, not a flat rate
- Sacramento, Placer, El Dorado, and Yolo counties
When to Get a Tree Health Assessment
You do not need a professional for every spotted leaf. You do need one when the pattern suggests structural risk or progressive decline — the situations where waiting a year changes the outcome.
916 Trees provides tree health assessments across Sacramento, Placer, El Dorado, and Yolo counties. We identify the problem, tell you honestly whether the tree is saveable, and put the findings in writing when a permit or insurance file needs documentation. Estimates are free and site-specific.
- Mushrooms or conks growing from the trunk, root flare, or major roots — the classic sign of internal decay.
- Canopy dieback that returns or expands each season despite normal watering.
- Bark splitting, sloughing off in sheets, or oozing dark fluid.
- A large tree — especially a protected native oak — showing any decline within falling distance of a house, driveway, or play area.
- Sudden lean, lifted soil at the base, or exposed roots after a wet winter.
- Before you spend money on treatments: an assessment confirms what you are actually dealing with, so you are not treating aphids on a tree that is dying of root rot.
Related reading
9 Signs a Tree Needs to Come Down
Nine warning signs a tree is hazardous or dying — and when removal is safer than trying to save it.
Keeping Trees Alive Through Sacramento Summers
Deep watering at the dripline, real mulch, and the heat-stress signs that matter — how Sacramento trees survive months of triple-digit heat.
When to Trim Oak Trees in California
The best window to prune native California oaks, why dry-season timing cuts disease risk, and the pruning mistakes that shorten an oak's life.
Frequently asked questions
Is my tree diseased or just heat-stressed?
- In Sacramento, the two overlap constantly, and heat stress often opens the door to disease. Scorched leaf edges appearing in July on an otherwise full canopy usually mean drought or heat stress. Dead branches scattered through the crown, bark falling off in sheets, mushrooms at the base, or leaves browning in spring when it is still mild point toward disease or pests. If a tree looks worse each year regardless of watering, get it assessed — decline rarely reverses on its own.
Will anthracnose kill my sycamore or ash?
- Almost never by itself. Anthracnose defoliates sycamores, London planes, and Modesto ash in wet springs, and the tree usually pushes a second set of leaves by early summer. The real cost is cumulative: repeated defoliation drains stored energy, and the twig dieback it causes builds deadwood that fails in wind. A tree that gets hit hard every spring benefits from pruning out infected deadwood and improving airflow, plus a plan to reduce other stresses.
Should I remove mistletoe from my trees?
- Yes, and the earlier the better. Broadleaf mistletoe is a parasitic plant that taps directly into the branch for water and nutrients — a heavy load weakens the tree and makes limbs more likely to fail in storms. Simply pulling off the visible clumps does not work; the roots stay embedded and regrow. Effective control means pruning infected branches back well past the attachment point, which is climbing work on the mature Modesto ash and oaks where it is most common.
Can oak root fungus (Armillaria) be cured?
- No. Once Armillaria is established in the root system there is no treatment that eliminates it. Management is about slowing it down and deciding whether the tree is still safe: keeping irrigation and soil off the root crown, avoiding trenching through the root zone, and monitoring for the honey-colored mushrooms and white fungal mats under the bark. Because Armillaria rots the roots that hold the tree up, an infected oak near a house or driveway needs a professional stability evaluation, not a wait-and-see approach.
My tree drips sticky sap on the car — is it sick?
- Probably not sap. That sticky film is almost always honeydew, the sugary excretion of aphids or scale insects feeding on the leaves — in Sacramento the usual suspects are hackberry, tulip tree, crape myrtle, and ornamental plums. Honeydew itself does not seriously harm a mature tree, though the black sooty mold that grows on it looks ugly. Heavy, repeated infestations can signal a stressed tree, so it is worth an assessment if the problem worsens year over year.