Phytophthora: The Root Rot That Loves Wet Feet

Not all tree problems start above ground. Some of the most damaging threats are hiding beneath the soil — and Phytophthora is one of the biggest troublemakers.

Although often called a fungus, Phytophthora is technically a water mold. It thrives in overly wet, poorly drained soils where tree roots struggle to breathe. Once established, it attacks the fine roots responsible for absorbing water and nutrients.

Ironically, trees suffering from Phytophthora often look drought-stressed even when the soil is soaking wet. Leaves may yellow, canopies thin, growth slows, and branches begin dying back as the damaged roots lose their ability to support the tree.

In severe cases, dark bleeding cankers can develop near the base of the trunk, signaling advanced infection.

The best defense against Phytophthora is healthy soil and good drainage. Trees like moisture — but they don’t want to live in a swamp. Proper mulching, avoiding overwatering, and protecting soil structure all help keep root systems healthy and resilient.