DiseaseHigh Severity

Thielaviopsis Decline

Thielaviopsis basicola

A soilborne fungal disease that causes root rot in elm and madrone trees. The fungus lives saprophytically in soil and typically enters roots through wounds caused by nematodes. Most problematic in heavy, cold, slightly acid to alkaline soils well supplied with humus.

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Madrone tree showing symptoms of Thielaviopsis decline with yellowing foliage

Identification & Symptoms

What to Look For

Root rot leading to yellowing of foliage
Dieback of branches progressing through crown
Basal stem discoloration extending 6 inches above soil line
General decline and weakening of tree
Eventually fatal if untreated

Potential Damage

Progressive root system destruction
Vascular disruption from root rot
Branch dieback and crown thinning
Tree mortality in advanced cases
Reduced tree stability from root loss

Lifecycle

Fungus lives saprophytically in soilEntry through nematode feeding woundsProduces colorless cylindrical conidia in chainsForms dark thick-walled resting spores (chlamydospores)Spores carried by nematodes into root systemsGermination tubes grow through nematode feeding wounds

Professional Treatment Approach

1

Improve soil drainage and aeration

2

Reduce nematode populations in soil

3

Avoid wounding tree roots during maintenance

4

Fungicide soil treatments for prevention

5

Remove severely affected trees to prevent spread

6

Plant resistant species in affected areas

Recommended Mauget Products

Fungisol

Professional-grade treatment specifically effective against thielaviopsis decline.

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Arborfos

Professional-grade treatment specifically effective against thielaviopsis decline.

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