Emerald Ash Borer & the Mid-South's Other Tree Killers

Emerald ash borer

EAB is a small metallic-green beetle whose larvae tunnel through the layer of tissue just under an ash tree's bark — the layer that moves water and sugar. Enough tunnels and the tree starves. It does not slow down, it does not stop, and untreated ash mortality in infested areas approaches total.

What to look for:

• Thinning canopy starting at the top. The first symptom, and the easiest to miss.
• Epicormic sprouts — a fuzz of new shoots erupting from the trunk and lower branches. The tree is panicking.
• D-shaped exit holes about an eighth of an inch across. Distinctive, and the tell.
• Bark splitting vertically, with S-shaped tunnels visible underneath.
• Heavy woodpecker activity — flecked, blonde patches where birds have stripped bark chasing larvae. Often the very first thing anyone notices.

And do not move the firewood. Hauling unseasoned ash between counties is the main way EAB travels. Burn it where it grew.

Hypoxylon canker — the oak killer nobody names

You will see a smooth, silvery-tan or olive patch where a section of bark has sloughed off an oak trunk, often with a powdery surface. That is hypoxylon.

It is an opportunist. The fungus is already present in most oaks and does nothing until the tree is weakened — drought, root severance from a driveway or trench, compaction from construction traffic, grade change. Then it moves.

Hard truth: by the time hypoxylon is visible, the wood underneath is already decayed and the tree is usually structurally compromised. There is no treatment. This is a removal conversation, and it is usually an urgent one, because the failures are sudden.

Bacterial leaf scorch

Very common in the older pin and willow oaks across Memphis, Germantown and Collierville. Leaf margins brown starting in mid to late summer, often with a narrow yellow band between the dead edge and the green center. It returns earlier and worse each year, working through the canopy branch by branch.

It is bacterial, it is systemic, and there is no cure — but decline can take a decade or more, and good care buys real time. Water deeply during drought, keep the root zone mulched properly, avoid fertilizing hard, and prune out declining wood.

Crepe myrtle bark scale

White or grey felty specks on trunks and branches, and then black sooty mold coating everything below. Widespread across the Mid-South. It rarely kills the plant but it looks terrible and it reduces bloom significantly. It is treatable, and the sooty mold weathers off once the scale is controlled.

Pine bark beetles

Popcorn-sized blobs of pitch on the trunk, sawdust in the bark crevices, and a crown that goes from green to yellow to red faster than seems possible. Southern pine beetle and Ips beetles hit drought-stressed and damaged pines.

Once a pine is fading, it is over — and the priority becomes removing it promptly so the emerging beetles do not move into the pines next door. This is one where waiting genuinely costs your neighbors.

Ambrosia beetles

Thin protruding strands of compacted sawdust, like toothpicks, on young trunks in early spring. They attack stressed young trees, especially recently transplanted ones. Usually a symptom that something else — planting depth, drainage, drought — was already wrong.

The one that is not a disease at all

A large share of the "my tree is dying" calls we run turn out to be none of the above. They are:

• A buried root flare. If the trunk goes into the ground like a telephone pole instead of flaring out, it is planted too deep or mulched too high. This kills trees slowly and it is completely reversible if you catch it.
• Mulch volcanoes. Mulch piled against the trunk holds moisture against bark that is not built for it, and invites rot and rodents. Mulch goes in a flat ring, not a cone, and it never touches the trunk.
• Construction damage. Trenching, grading, compaction, driveway pours. The tree dies two or three years later and nobody connects it to the work.
• Clay soil and drainage. Heavy Memphis clay drowns roots in a wet spring and bakes them in an August drought.

We look at the base of a tree before we look at its leaves, because that is where the answer usually is.