Every week we walk properties across Sugar Land, First Colony, and the greater Houston metro where a homeowner says the same thing: "It looked fine last summer." Houston trees rarely die overnight. They decline over two to four seasons, and nearly every fatal problem we deal with — oak wilt, hypoxylon canker, root rot — leaves visible evidence long before the tree is past saving. Homeowners who catch that evidence early keep their trees. The ones who don't end up calling us for a removal quote instead.
This guide is the hub for everything we've written about Houston tree health. It answers the questions we hear most on inspection visits, and it links to our deeper guides on each disease and pest so you can go exactly as far down the rabbit hole as your tree requires.
How do I know if my tree is sick?
Run a visual triage from the top of the canopy down, twice a year — once at spring green-up, once in late summer. A healthy tree carries full, evenly colored foliage across the whole crown. Look for five things:
- Crown thinning — you can see more sky through the canopy than you could last year
- Tip dieback — branches dying from the tips inward, toward the trunk
- Leaf abnormalities — browning veins, yellowing tissue, spots, early drop
- Trunk problems — bark falling off in patches, cavities, cracks, mushroom-like conks
- Base problems — mushrooms at the root flare, heaving soil, new cracks in the ground
One symptom means watch the tree. Two or more means get a professional opinion. The most useful rule of thumb: leaf-level problems are usually minor, while crown-level and trunk-level problems are usually serious.
What diseases hit Houston trees hardest?
Three diseases account for the large majority of the disease-related removals we do in the Houston metro: oak wilt, hypoxylon canker, and root rot. Here's how to recognize each one.
Is it oak wilt?
Oak wilt is the most destructive tree disease in Texas, and it's established in parts of the Houston metro. The diagnostic symptom on live oaks is veinal necrosis — leaf veins turning brown or yellow while the tissue between them stays green. Almost nothing else produces that pattern. Red oaks (Shumard, water oak) skip the subtlety: the whole crown browns in 4–6 weeks and the tree usually dies within a season. The fungus spreads through root grafts between oaks growing within about 50 feet of each other, and through sap beetles that visit fresh pruning cuts — which is why we never prune oaks between February and June. Our full oak wilt guide covers prevention, trenching, and fungicide injection; our early-identification guide shows exactly what the leaf patterns look like week by week.
What does hypoxylon canker look like?
Hypoxylon is the opportunist. The fungus lives latently on most Houston oaks and does nothing — until drought, construction damage, or root stress weakens the tree, and then it colonizes fast. It was relatively rare here before the 2011 drought; since then it's become the most common decline we see on stressed oaks across the metro. The telltale sign is bark cracking and sloughing off in large patches, exposing a smooth gray-green fungal surface underneath that later turns black and powdery. Here's the hard truth we tell homeowners on-site: by the time that stroma is visible, the tree is usually past saving. Hypoxylon doesn't kill healthy trees — it finishes off stressed ones. The real defense is upstream: irrigation during drought, a proper mulch ring, and keeping construction equipment off the root zone.
Is root rot killing my tree from below?
Root rot is the disease Houston's soil practically invites. Several fungi — Phytophthora, Armillaria, Ganoderma — all thrive in saturated ground, and our clay holds water for days after heavy rain. Symptoms move slowly: crown thinning that progresses over 2–3 years, dieback starting at the branch tips, smaller leaves on new growth, and mushrooms or shelf-like conks emerging at the root flare. The dangerous part is what you can't see. A tree can carry a green, full-looking crown on roots that are already soft and rotted — and that tree fails in the next 60 mph wind. If you see fungal growth at the base of a trunk, treat it as urgent, not cosmetic. Our root rot guide covers the below-ground symptoms and which species handle wet clay best.
Which pests actually matter for Houston trees?
Most leaf-chewing insects are cosmetic — a healthy tree shrugs them off. Three categories deserve real attention. First, wood borers: small round or D-shaped exit holes in bark, fine sawdust ("frass") in bark crevices, and woodpeckers hammering one specific tree all point to borers, which attack stressed trees and include emerald ash borer — the reason we no longer plant ash. Second, scale insects: white waxy bumps on bark plus black sooty mold on surfaces below the tree, with crape myrtle bark scale the most aggressive since it reached Texas around 2004. Third, web-builders: fall webworms wrap pecan branch tips in silk nests in late summer — ugly but rarely fatal to mature trees — while bagworms can genuinely defoliate cedars and junipers. Our full pest and disease field guide covers identification and what actually works for each.
Why are my tree's leaves turning yellow?
The pattern of the yellowing matters more than the yellowing itself. Yellow leaf tissue with veins that stay green is iron chlorosis — Houston's alkaline clay locks up iron even when the soil contains plenty, and pecans show it constantly. That's treatable with soil-applied iron chelate. The reverse pattern — veins turning brown or yellow while the tissue between them stays green — is the oak wilt red flag, and it means call an arborist this week, not this season. Uniform yellowing across the whole crown usually points to drought stress or root damage rather than disease. And yellow-gold pecan leaves in late October are just autumn. Our pecan yellowing guide walks through all five causes and how to tell them apart, with the fix for each one.
What does Houston's clay soil do to tree health?
Houston's "gumbo" clay is behind more tree problems than any single pest. It holds water for days after our 50+ inches of annual rain, and saturated roots can't get oxygen — weakened, oxygen-starved roots are exactly what root-rot fungi need. The same clay is alkaline, which locks up iron and drives the chlorosis we see on pecans and pin oaks. Then drought flips the problem: gumbo shrinks and cracks as it dries, tearing fine roots and stressing trees into hypoxylon territory. What helps: don't irrigate established trees in normal years (added sprinkler water pushes borderline soil into saturation), keep mulch 6 inches off the trunk flare, fix standing-water spots with French drains or grading, and plant species that tolerate wet clay — live oak and bald cypress handle it; loblolly pine and pin oak struggle.
Can Houston's freezes and droughts make a tree sick?
Yes — and often on a delay that fools homeowners. The February 2021 freeze and the 2023 drought both left Houston trees stressed in ways that didn't fully show until one to three growing seasons later, when hypoxylon and borers moved into weakened trees that "survived" the event itself. That's the pattern with climate stress here: the weather event opens the door, and the opportunists walk through later. Two practical rules follow. First, deep-water established trees through real droughts — a slow soak at the drip line once a week beats daily sprinkler misting. Second, don't rush to remove a freeze-damaged tree. Most Houston live oaks that looked rough after the 2021 freeze flushed back out by late spring. Wait for the spring flush before making any removal decision, and scratch-test twigs for green tissue in the meantime.
When is a sick tree saveable — and when does it need to come down?
We turn down removal jobs every month — trees the homeowner assumed were lost that had years left with the right care. Generally saveable: iron chlorosis, anthracnose and other leaf-spot diseases, webworms and light scale, drought stress, and canopy loss under about 25%. Generally not: a hollow running more than a third of the way through the trunk, more than 50% of the canopy dead, rotted or heaving roots, established hypoxylon with visible stroma, or a lean that's actively worsening with fresh cracks in the soil. A green crown doesn't override a failed root system — structure beats foliage every time. Our guide to the five real removal signs covers each threshold in detail, including the symptoms that look alarming but aren't.
How do I keep a healthy tree from getting sick?
Almost every disease in this guide preys on stressed trees, so prevention is mostly stress management. Prune on a schedule — every 3–5 years for established trees — using ANSI A300 cuts, never topping. Prune oaks only November through January, when the sap beetles that vector oak wilt are dormant, and seal every oak cut. Maintain a mulch ring out toward the drip line, 2–3 inches deep, kept 6 inches off the trunk. Deep-water established trees during real droughts like 2023's — a slow soak at the drip line once a week. Keep construction equipment, trenching, and grade changes out of the root zone. Our tree trimming and pruning service handles the schedule and the standards; for the signature species, our live oak care guide is the complete year-round manual.
When should I call an arborist about a sick tree?
Call when you see two or more of the triage symptoms above, any suspicion of oak wilt (weeks matter — root grafts spread it to neighboring trees), mushrooms or conks at the base of a trunk, bark sloughing off in patches, or a new lean after a storm. Don't call in a panic over leaf spots, sap drips, or a few dead twigs — those have a hundred harmless causes. Crown dieback almost never does. Most homeowners over-react to cosmetic leaf issues and under-react to the structural ones, and the structural ones are what put trees on houses. We do free tree-health assessments across Sugar Land, Fort Bend County, and the Houston metro, and we'll tell you straight: saveable, marginal, or done. Call (281) 626-9111 or book an assessment online.