Although it is true that more plant diseases are caused by fungi than any other type of pathogen, only 11% of all fungi are capable of causing disease in plants at all. The grand majority of fungi are saprophytes. That is they survive by breaking down organic matter and absorbing nutrients from it. In many cases, the mushrooms sprouting in the woodchip mulch or pushing up through the lawn are not harming the nearby plants, but are working on breaking down woodchips, plant debris or other organic matter.
Two saprophytic fungi commonly found in Minnesota landscapes are stinkhorns and birds nest fungi.
Several kinds of stinkhorns can be found in Minnesota. These fungi start as round to oval egg like structures. When mature a spongy looking stalk with a slime covered cap emerges. Often the remains of the 'egg' can be seen at the base of the mature stinkhorn. Stinkhorns get their name from the smelly sticky slime that caps the mushroom. This slime is full of fungal spores. The smell attracts flies, which will carry the spores to new locations. Stinkhorns can be found in mulched beds, under trees and shrubs and occasionally in lawns.
Bird's nest fungi
There are two common genera of bird's nest fungi found in Minnesota; Cyathus sp. and Crucibulum sp. These two fungi form tiny cup shaped structures with small round disks inside known as peridioles. The cups are designed to catch rain drops and send the peridioles (full of fungal spores) flying to a new location. These hard dark disks can often be found nearby clinging to plants, siding, or whatever else is in the way. Bird's nest fungi commonly grow on woodchip mulch in landscapes.
Mushrooms and Shelf Fungi of Plant Pathogens
Mushrooms or shelf fungi that are growing directly on the trunk of the tree, out of the root flare or right at the base of the tree indicate that the tree is suffering from heart rot, root rot or butt rot. Trees suffering from internal wood rot may or may not have symptoms in the canopy. For example a honey locust with Ganoderma root rot may have a shiny brown shelf fungi growing at the base of the tree and several dead or wilting branches within the canopy. These branches have died because the trees rotted roots were no longer able to provide the nutrients and water they needed. In contrast a cottonwood tree with heart rot may have a full healthy green canopy despite internal rot in the trunk of the tree. Regardless of how healthy the canopy appears, all three types of rot can greatly weaken the tree due to internal decay. www.treesaregood.org) as soon as possible. These professionals can help determine the structural stability of the tree and recommend appropriate action.