DiseaseHigh Severity

Armillaria Root Rot

Armillaria mellea (also known as Oak Foot Fungus, Oak Root Rot)

A widespread fungal root disease attacking most tree species worldwide. Often associated with stressed trees, it spreads through root contact and can survive for decades in infected stumps. The disease causes gradual decline and can predispose trees to bark beetle infestation.

Peak Season: Active year-round, symptoms most visible during growing season, mushrooms appear in fall
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Armillaria root rot showing characteristic mushrooms and root damage

Identification & Symptoms

What to Look For

Thinning crowns and declining growth increments
Foliage chlorosis and reduced leaf size
Heavy basal resin flow in conifers
Trees may appear to die suddenly or be wind thrown
White mycelia fans under bark of roots and lower stems (diagnostic)
Black or brown rhizomorphs (shoestring-like structures) under bark
Golden-colored mushrooms around tree bases in fall
Yellow, stringy, malodorous advanced decay

Potential Damage

Disrupts water and nutrient transport in root system
Causes gradual decline evidenced by small, yellowish leaves
Trees may wilt suddenly during stress periods like drought
Can cause wind throw due to root system deterioration
Predisposes trees to bark beetle infestation
Often occurs in distinct disease centers but may have scattered distribution

Lifecycle

Fungus spreads primarily through root contact between infected and healthy trees. Rhizomorphs can grow short distances through soil to infect nearby roots. Spores can spread but this is uncommon. Fungal mycelia can survive at least 35 years in stumps and roots before being replaced by other organisms.

Professional Treatment Approach

1

Improve drainage and reduce soil compaction

2

Avoid wounding trees during maintenance

3

Proper site-species matching during planting

4

Remove infected stumps and root systems when possible

5

Maintain tree health through proper watering and fertilization

6

Fungicide injection may help in early stages

Recommended Mauget Products

Fungisol

Professional-grade treatment specifically effective against armillaria root rot.

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Tebuject 16

Professional-grade treatment specifically effective against armillaria root rot.

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