With mild days and cool, humid nights, Louisiana’s fungal flora is making its presence known! Lots of mushrooms are popping out, and the ringless honey mushrooms (Desarmillaria caespitosa) are commonly found in our landscapes this time of year. These are tan to brown mushrooms that occur in clumps, growing out of rotting wood, especially out of decaying hardwood roots and stumps. Any mushroom is the spore-producing body of a fungus that is digesting organic matter, in this case, the carbohydrate cellulose. The mycelium (main fungal body) will continue digesting the stump or roots long after the mushrooms have shed spores and decayed away. So named because this species lacks the ring (annulus) that is found encircling the stalk (or stipe) in many other mushrooms. The surface of whatever the cluster of mushrooms is growing out of may appear to have a white crust. This crust is the tens of millions of spores the fungal fruiting body has shed for reproduction. Many of the dust-like spores are carried away by wind currents.
Ringless honey mushrooms and several other species in the genus Armillaria and its segregate genera can cause a problem in trees and shrubs called Armillaria root rot, or oak rot. This has been a major problem on peach trees in northern Louisiana, and as the name implies, can affect oak and other hardwood species in the landscape. The mycelium grows throughout the cambial region in fan-shaped patterns, digesting cellulose and lignin. String-like structures called rhizomorphs grow through the soil on the surface of roots. Rhizomorphs can become dormant, exist for years in roots or stumps of dead trees, and become active again. Mushrooms will grow in clusters out of the decaying tissue and produce white spores.
Armillaria root rot is difficult to manage once infection occurs and is always fatal to the tree it infects. Large trees may take longer to evidence symptoms once signs of the fungus appear. Smaller trees will die in a matter of months to a year or two. Diseased material should be removed immediately after it is noticed. Selecting resistant varieties is also a key step to controlling Armillaria root rot.
As with most mushrooms, the question of edibility always comes up. No wild mushroom should be consumed unless the identity and safety is first confirmed by an expert in mycology.
The LSU AgCenter and the LSU College of Agriculture