What is Black Knot Disease?

Black knot is a common fungal disease primarily affecting Prunus trees, including plum and cherry varieties.

Understanding Black Knot

Based on the provided reference, black knot is identified as:

A common fungal disease.
It affects trees in the Prunus genus.
This includes a variety of plum and cherry trees, specifically mentioned as ornamental, edible, and native plum and cherry trees.
The characteristic symptom is the formation of hard swollen black galls.
These galls are described as tumor-like growths.
They typically form on branches, but can occasionally appear on trunks.
Many Prunus trees have a degree of tolerance to black knot.

Essentially, when someone asks about "knot disease" in the context of plum and cherry trees, they are most likely referring to Black Knot.

The most recognizable sign of black knot is the distinctive gall formation.

Appearance: Initially, they might appear as greenish-brown swellings that darken and harden over time.
Mature Galls: They become hard, rough, and black, often irregularly shaped.
Location: Primarily found on branches, causing swelling and distortion. Less commonly seen on the main trunk.
Impact: While many trees tolerate the disease, severe infestations can weaken branches, reduce fruit production, and even kill parts of the tree or the entire tree over time.

Here's a quick look at the key characteristics:

Characteristic	Description
Cause	Fungus
Affected	Prunus trees (Plum, Cherry)
Symptoms	Hard, swollen, black galls
Location	Branches, occasionally trunks
Severity	Variable; many trees are tolerant

As highlighted by the reference, black knot is particularly problematic for Prunus species. This includes:

While some varieties within these groups are more susceptible than others, black knot can potentially infect any tree in the Prunus family.

Understanding the symptoms and affected trees is crucial for identifying and managing black knot disease in your landscape or orchard.