Fungi are a natural part of landscapes. They go unnoticed until we see signs of them or symptoms on plants. Signs can be mold, mushrooms, decay, or rusty colored dust on lawn mowers. Symptoms may include leaf spots or discolored areas on plant stems.
If mold or mushrooms are noticed on wood mulch in a landscape bed, these are not a concern for nearby plants. If noticed on a tree trunk or branch, there is cause for concern and closer inspection is needed. Fungal symptoms on plant leaves may or may not be a concern.
When mold or mushrooms are noticed on wood mulch in a plant bed, I’ve been asked if the fungus could be harmful to nearby plants. The answer is no. Wood mulch is organic. Like all organic mulch, it decomposes over time adding valuable organic matter to soil. This is a benefit of using organic mulch.
When we see mold or mushrooms, we are seeing the fungal fruiting body that produces new spores. Decay fungi are not pathogens and their spores will not infect nearby plants. They are a sign of nature doing what nature is supposed to do and are not a concern to plants growing in or near the mulched bed.
While we expect wood mulch to decompose, when mold or mushrooms are seen on a living tree trunk, branch or near the base of a tree, this is cause for concern. These fungal fruiting bodies are a sign of decay in the tree or roots which can increase the risk of tree failure.
Trees with mold or mushrooms may not need to be removed immediately. They do need to be inspected by a certified arborist or experienced tree care professional. Ideally, the inspector would be tree risk assessment qualified (TRAQ). Certified arborists can be located on the Nebraska Arborist Association website.
Trees usually decay from the inside out. If the tree is actively growing, it is adding sound wood to the outer part of the trunk. If a tree has a solid outer core of strong wood, it less of a risk than a tree without a solid outer core. Any tree, with or without decay, can fail with enough force from wind, snow or ice.
Signs of mold or mushrooms on a tree are of greater concern if the tree has open cavities with visible signs of decay; the fungal growths are on branches with cracks, weak branch unions, or other defects; or a very large branch is decayed.
The presence of sound wood can be checked by tapping the area near fungal growths with a soft mallet to see if it sounds hollow. If it does not sound hollow, this does not mean the tree is okay and does not need further inspection. But if it sounds hollow, inspection should be done sooner than later.
By: Kelly Feehan, Extension Educator
Release: Week of November 25, 2024