DiseaseHigh Severity

Phytophthora cactorum

Phytophthora cactorum

A soilborne water mold pathogen causing crown rot, collar rot, root rot, and stem rot on numerous tree species. This aggressive pathogen can kill trees in one growing season or cause chronic decline over multiple years. Favored by cool, wet conditions and poorly drained soils.

Peak Season: Most active during cool, wet weather in early spring and fall. Trees most susceptible during bloom period. Cool temperatures and high soil moisture favor infection.
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Phytophthora cactorum infection showing characteristic water-soaked lesions and tissue damage typical of this water mold pathogen

Identification & Symptoms

What to Look For

Cankers at or below soil line extending into root system
Infected bark appears brown and slimy when wet
Cambium and phloem show orange to reddish-brown discoloration
Poor vegetative growth and reduced vigor
Chlorotic foliage that may turn purple in autumn
Progressive crown thinning and dieback
Tree death in one season or gradual decline over years

Potential Damage

Girdling cankers leading to tree death
Root system destruction and dysfunction
Vascular tissue invasion and disruption
Rapid tree mortality in severe infections
Chronic decline reducing tree value and stability
Economic losses in orchards and landscapes

Lifecycle

Survives as thick-walled oospores (resting spores) in infected tissue and soil for extended periods. Under moist conditions, oospores germinate forming sporangia that release motile zoospores in free water. Zoospores swim to roots or lower trunks, germinate, and infect through wounds or direct penetration.

Professional Treatment Approach

1

Apply systemic fungicides like Fungisol for root and crown protection

2

Improve soil drainage around affected trees

3

Avoid deep planting and soil grade changes near trees

4

Remove infected trees to reduce soil inoculum

5

Professional soil treatment may be necessary in severe cases

6

Preventive treatments for high-value trees in infested soils

Recommended Mauget Products

Fungisol

Professional-grade treatment specifically effective against phytophthora cactorum.

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Mycoject Ultra

Professional-grade treatment specifically effective against phytophthora cactorum.

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