American Tree Experts

Tree Fungus: A Comprehensive Guide to Identification and Prevention

Why you should care – The hidden dangers of tree fungus and how to stop them

Your trees face various challenges throughout their lifetime, including the tree fungus. These fungi manifest in diverse forms, from seemingly benign shelf mushrooms to the more deadly Rhizosphaera Needle Cast. While you can’t completely cure a tree of fungus, you can restore your tree’s health and vitality. Read this guide to identify and mitigate the impact of tree fungus to keep your trees healthy and thriving.

What is Tree fungus?

  • Fungi are diverse spore-producing organisms and thrive on organic matter, including molds, yeast, mushrooms, and toadstools. These fungal species grow across North America and worldwide. Fungal infections can occur in several ways. For instance, mushrooms on a tree trunk often indicate the presence of wood decay fungi.

These infections can impact any part of a tree, resulting in infected branches, discolored tree bark, or dead wood. However, many fungi play beneficial roles, actively participating in decomposition and nutrient cycling within diverse ecosystems. Additionally, these fungi contribute to carbon dioxide fixation in the soil, preventing climate change.

Types of Fungi

  • While many fungi establish friendly relationships with trees in symbiosis, certain types of fungi can pose a threat and cause substantial damage. Two particularly hazardous types of fungus are root rot and collar rot, each capable of wreaking havoc on trees. Let’s explore these menacing varieties:

1. Root Rot

  • Root rot targets the roots of trees and indoor and outdoor plants. Infected tree roots transform, becoming slimy and mushy, hindering their ability to absorb water, oxygen, and nutrients.

Various fungi contribute to root rot, including:

Armillaria (Shoestring Fungus)

  • They affect various plants, including palms, succulents, and trees. Initial signs include dropping leaves, yellowing, and upper limb dieback.


  • They typically infect trees and plants in poorly drained areas, leading to rapidly wilting and dying leaves and branches, especially in heat.


  • Often linked to grass die-off but can also infect conifers and hardwoods, causing leaf, branch, and limb loss or stunted growth.


  • Commonly associated with stressed or injured trees, causing wilting, yellowing leaves, and decayed roots in various tree species.


  • Primarily impacts seedlings and young trees, while rot symptoms in older trees may be attributed to another fungus.

Thielaviopsis (Black Root Rot)

  • Particularly threatening to palms, this fungus consumes the plant from the inside out, ultimately leading to its collapse.

They are typically associated with areas of poor drainage or persistent moisture. Addressing the issue promptly with expert guidance can often save the tree from irreversible damage.

2. Collar Rot

  • tree fungusCollar rot is a fungal infection that targets the collar. The collar is the portion right above the ground that widens beneath the trunk and above the root flare. The collar requires its place above ground to receive essential light nutrients and, crucially, to remain dry. Excessive water exposure or burial in the soil creates a favorable environment for collar rot. While Phytophthora is a common cause, several other species, both host-specific and more general, can contribute to collar rot.

Fruit trees, in particular, face increased vulnerability. Recognizing collar rot involves identifying symptoms such as cankers on the trunk between the soil line and crown roots, scattered yellow leaves appearing mid-season, a reddish or purple tint in the foliage by late September, and sparse foliage coupled with reduced vigor.

If you fear that your trees and plants are suffering from fungus, then waste no time and contact American Tree Experts. We provide effective and proactive Disease Management for plants and trees. Call us at (973) 744-6091 to get a free estimate of our services. We operate in Mont Clair, New Jersey, and nearby areas.

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