Blueberry Root Rot — Signs, Causes and Recovery

Root rot is one of the most damaging things that can happen to a blueberry, and by the time the symptoms are visible above ground the damage below ground is already severe. The primary cause is Phytophthora cinnamomi, a water mould that thrives in saturated, poorly drained soil and attacks the fine fibrous roots that blueberries depend on. Understanding the conditions that allow root rot to develop is as important as treating the immediate problem, because a plant returned to the same conditions will simply develop root rot again.

Recognising the symptoms

Above ground, root rot first shows as a general dulling of leaf colour from bright green to a grey-green, followed by wilting that is most noticeable during warm parts of the day even though the soil is moist. The leaves then yellow, often appearing similar to iron deficiency, and in severe cases the plant wilts and dies progressively over days or weeks. If you carefully dig and wash the roots, healthy blueberry roots are white and firm. Roots affected by Phytophthora are brown, mushy and disintegrate easily. The fine hair roots are killed first, leaving only the larger structural roots, which cannot absorb water and nutrients on their own.

Conditions that cause root rot

Phytophthora is ubiquitous in soils but only causes disease in waterlogged or persistently saturated conditions. Blueberries planted in heavy clay, compacted soil, low-lying sites, or in containers without adequate drainage holes are at highest risk. Overwatering a container plant, or a plant hit by an extended wet period in poorly drained ground, is the classic scenario. Once the pathogen establishes in a site, it persists in the soil for years, making replanting in the same spot without improving drainage a poor choice.

Can an affected plant recover?

Mild cases can recover if the drainage problem is fixed immediately. Stop all watering, improve drainage if possible, and consider lifting the plant and replanting in a raised bed or large container with free-draining acidic compost. Trim back any obviously dead roots to clean tissue. A plant that has lost more than two-thirds of its root system is unlikely to recover and should be removed. Do not replant a blueberry in the same hole without first fundamentally improving drainage.

Prevention is the whole strategy

Where the soil is heavy or drainage uncertain, raised beds filled with a mix of acidic compost and composted bark are the most reliable solution. Large containers with generously sized drainage holes and a free-draining compost mix work equally well. These approaches move the roots out of the problematic soil entirely rather than trying to amend it in place.