What is Phytophthora root rot?

It is a root and root-collar rot caused by Phytophthora, a soilborne water mold (an oomycete) that thrives in wet, poorly drained soil. It destroys fine roots and the root collar so the plant cannot take up water, and it slowly declines even though the ground is wet. In Central Texas it is common on Indian hawthorn, photinia, boxwood, holly, and some fruit trees.

How is Phytophthora root rot different from drought stress?

They look alike, wilting, thin canopy, off-color leaves, but the cause is opposite. Drought improves with water. Phytophthora root rot keeps declining despite wet soil or poor drainage, because the roots are rotting, not thirsty. A dark, rotted root collar and sparse fine roots point to root rot rather than drought.

Can Phytophthora root rot be cured?

There is no spray that cures it. Management means fixing the site: improve drainage, reduce irrigation, set plants at the correct depth, and replace dead plants with resistant species. Phosphonate (phosphorous acid) products can suppress the disease on high-value plants as part of that plan, but they do not eliminate the pathogen and are best applied by a professional alongside cultural fixes.

Plant Health Care • Central Texas

When a shrub rots from the roots up

A hedge dying out in a patch, a shrub that wilts no matter how much you water it: that is the signature of Phytophthora root rot, a soilborne water mold that thrives in wet, poorly drained ground. It is one of the most common, and most misread, killers of Central Texas landscape plants.

Get it diagnosed → Call 512-800-3566

Wet feetPoor drainage drives it

Looks like droughtBut water makes it worse

Site firstNo spray cures it

A boxwood hedge with a section killed off by Phytophthora root rot while the rest stays green

A container holly thinning and browning as Phytophthora root rot destroys its root system

What it is

A water mold, not a dry-spell

Phytophthora is not a true fungus, it is a water mold that swims through wet soil and attacks the fine roots and root collar. Starved of a working root system, the plant declines even while the ground stays wet. That is the cruel trick of this disease.

It is most at home in poorly drained spots, low areas, heavy clay over caliche, beds that stay soggy, and around plants that are overwatered or set too deep. The pathogen is often already in the soil, waiting for the water to give it an opening.

What it attacks

The plants most at risk here

Plenty of species can get it, but a handful carry most of the trouble in Central Texas landscapes.

Central Texas hosts

The ones I see fail most often in local yards, especially when they sit in a low or overwatered bed.

Indian hawthornPhotiniaBoxwoodHollySome fruit trees

Broader susceptible species

The classic host list runs much longer, but several of these are cooler, wetter-climate plants you rarely see thriving in Central Texas to begin with.

RhododendronAzaleaDogwoodDaphneYew (Taxus)

Branch dieback and wilted, browning foliage on a rhododendron with Phytophthora root rot — Phytophthora dieback on a rhododendron, a classic host in cooler, wetter climates. The same root rot shows up here on Indian hawthorn and boxwood instead.

Tell them apart

Root rot or drought

They look almost identical from the canopy. The difference is in the water and the roots, and it changes everything about the fix.

Phytophthora root rot

Declines in wet soil

Keeps wilting and thinning even when the ground is wet
Often a low, soggy, or poorly drained spot
Dark, sunken, rotted root collar and sparse, brown fine roots
Can kill in patches, like a section of a hedge

Drought stress

Recovers with water

Perks back up after a good, deep watering
Usually on dry, exposed, or sandy sites
Roots are firm and healthy, just dry
Tends to affect plants evenly across the bed

How to manage it

Fix the site, not just the plant

There is no spray that cures Phytophthora. You beat it by taking away the water that feeds it and giving roots a chance to recover.

What works

Improve drainage, raise beds or regrade so water moves away from the root zone
Water less often, deep and infrequent, and keep it off the trunk and crown
Plant at the right depth, expose the root flare, never mound soil over it
Replace and replant dead spots with more resistant species suited to the soil

What does not

More water. It feeds the pathogen and finishes the plant faster
A bag of fertilizer. The roots cannot use it, and high nitrogen can make it worse
Counting on a spray. Phosphonates only suppress it, and only alongside drainage fixes
Replanting the same species in the same wet hole that just killed one

One Phytophthora is different

Sudden Oak Death is a reportable pathogen

Ordinary root rot is a site and water problem you can manage. But one species, Phytophthora ramorum, causes Sudden Oak Death and is a federally regulated, reportable disease. It is not established in Texas, and the goal is to keep it that way. If a tree is ever suspected of it, the right move is not to prune or treat it, it is to leave it undisturbed, avoid moving plant material or soil, and report it to Texas plant health officials for confirmation.

Shrubs dying in a wet spot? Let's check the roots

If a hedge is failing in patches or a shrub keeps declining no matter how you water it, send me a photo and tell me about the site. I can usually tell root rot from drought and point you to the fix that fits your soil.

Request an assessment → Call 512-800-3566

This page is educational and does not diagnose any specific plant. Root rot is confirmed by examining the roots and site, and treatment choices should follow that diagnosis, the product label, and local conditions. A suspected regulated pathogen such as Phytophthora ramorum should be reported to Texas plant health officials rather than treated.