Healthy trees fight off most pests and diseases on their own. Stressed trees don't. So the underlying message of this guide isn't really about specific pests — it's that a tree that's been pruned correctly, mulched properly, and watered during drought is mostly going to be fine. A tree that's been topped, mowed-against, drought-stressed, or root-damaged during construction is the one that bagworms or hypoxylon will move into.
That said, knowing what to look for buys you time. Here are the most common pest and disease problems we treat in the Houston metro, in rough order of how often we see them.
Oak wilt (Bretziella fagacearum)
The most serious tree disease in the Houston metro, period. Oak wilt is a fungus that kills live oaks and red oaks (Spanish oak, Shumard oak, water oak). It spreads two ways: through root grafts between adjacent oaks (which is why oak wilt often takes out an entire neighborhood block once it starts) and through sap beetles that visit fresh pruning cuts on healthy trees.
What to look for: On live oaks, look for veinal necrosis — the veins of individual leaves turning yellow-brown while the leaf tissue between veins stays green. The pattern progresses to leaf drop, then crown dieback. On red oaks, look for fungal mats forming under loose bark (a key diagnostic feature).
What to do: Get an ISA-certified arborist to confirm. The Texas A&M Forest Service maintains a detailed oak wilt resource. Don't prune oaks February through June. Our oak wilt guide covers prevention.
Hypoxylon canker (Biscogniauxia atropunctata)
An opportunistic fungus that lives latently on most oaks and only becomes pathogenic when the tree is stressed. Hypoxylon was relatively rare before the 2011 drought; since then it's become the most common decline we treat on stressed oaks across Houston.
What to look for: Bark cracking and falling off in large patches, revealing a smooth gray-green fungal stroma underneath. The stroma later turns black and powdery. By the time you see it, the tree is usually past saving — hypoxylon doesn't kill the tree directly; it colonizes a tree that's already dying from drought, root damage, or construction stress.
What to do: Address the underlying stress — proper irrigation, mulch ring, no root-zone disturbance — and hope. If hypoxylon is established, removal is usually the honest answer.
Anthracnose
A group of fungal diseases that cause leaf spotting and early leaf drop, especially common on sycamore, oak, and pecan. Anthracnose looks alarming in spring but rarely threatens established trees.
What to look for: Brown spots along leaf veins, distorted new growth, premature leaf drop in late spring.
What to do: Generally nothing — established trees outgrow it. Rake up and dispose of fallen leaves to reduce the next year's spore load. Avoid overhead irrigation that wets the foliage.
Bagworms (Thyridopteryx ephemeraeformis)
The most common pest call we get on cedars, junipers, and Italian cypresses. Bagworms are caterpillars that construct small bag-shaped cocoons from plant material and feed on the foliage.
What to look for: Small (1-2 inch) brown bags hanging from branch tips. The bags often look like they're part of the tree. Heavy infestations defoliate the host completely.
What to do: Hand-pick the bags in fall and winter and destroy them — each bag contains hundreds of eggs for next year's generation. For heavy infestations, treat with Bacillus thuringiensis (Bt) in late spring when larvae are small.
Scale insects
Several scale species attack Houston-area trees. Crape myrtle bark scale (CMBS) is the highest-profile — it arrived in Texas around 2004 and has spread aggressively. The Texas A&M AgriLife Extension Service maintains excellent scale identification resources.
What to look for: White waxy bumps on bark, often accompanied by black sooty mold on leaves and surfaces below the tree (the mold grows on honeydew the scale insects excrete).
What to do: For CMBS, systemic insecticide applied in spring is the standard treatment. For other scale species, dormant oil applications in winter often suffice. Heavy infestations need an arborist.
Wood-boring insects
Several borer species attack Houston-area trees, including emerald ash borer (recently arrived in our area and the reason we don't plant ash anymore), red oak borer, and various pine bark beetles. Borers generally attack stressed trees rather than healthy ones — so the underlying treatment is stress reduction, not insecticide.
What to look for: Small round or D-shaped holes in bark, fine sawdust ("frass") at the base of the tree or in bark crevices, woodpecker activity concentrated on specific tree(s).
What to do: Get an arborist to identify the species. Some borers can be treated with systemic insecticide; others (emerald ash borer in late stages) cannot. Address underlying stress.
Root rot diseases
Several root-rot fungi (Phytophthora, Armillaria, Ganoderma) attack Houston-area trees, especially in poorly-drained clay soils. Our root rot guide covers identification.
What to look for: Crown thinning, branch dieback starting at the top, mushrooms growing from the root flare or buttress roots, cracks in the soil at the base of the tree.
What to do: Get an arborist to inspect. Root-rot is hard to treat once established; prevention through proper drainage is the realistic answer.
When to call an arborist
Most homeowners over-react to leaf-level cosmetic issues (anthracnose, minor scale) and under-react to crown-level structural issues (early hypoxylon, oak wilt, root rot). The general rule: if the canopy is thinning, if branches are dying back from the tip toward the trunk, or if any of the major diagnostic indicators above are visible, call an arborist. Leaves curl and spot for a hundred reasons. Crown dieback is almost always serious.
We do free inspection visits across the Houston metro. Get in touch if you're seeing symptoms you can't identify.