Armillaria Root Rot
Have you noticed a tree or shrub that is wilting, with very little foliage, and the leaves that do remain look dry and shriveled while hanging in place?
This often happens in a hedge row; you’ll notice only one plant with symptoms while the rest look healthy. Some of the plants you may see this happen to include loquats, ligustrum, and azaleas, but many other trees and shrubs are susceptible. But susceptible to what? What is happening to your plant? If what we’ve described has happened in your landscape, mushroom root rot may be to blame.
Mushroom root rot, also called Armillaria root rot, is caused by a genus of fungi, Armillaria spp., that gets inside a plant and prevents it from properly absorbing water. Here in Florida, Armillaria tabescens is the most common species infecting trees and shrubs.
The first thing you’ll notice is a decline in your plant’s health. Unfortunately, by the time you see this decline, the disease is already in the plant. Next, you might see clusters of yellow to honey-colored mushrooms; these are the Armillaria fungi fruiting bodies. These mushrooms emerge when conditions are favorable, usually during the fall and winter in Florida, when there's enough moisture.
Armillaria can infect a wide range of trees like oaks and hickories, as well as many hardwoods and conifers. The fungus infects the roots of trees and shrubs causing them to decay, weaken, and even die. Infected plants can have fading, wilting, or thinning foliage; overall decline; dead branches; branch or trunk failure; dieback; or stunted growth. Most of the time in Florida, Armillaria is a secondary condition that will affect an already-stressed tree, so the best way to prevent infection is to keep your trees and shrubs healthy, although there are instances where the fungus has attacked an otherwise healthy tree.
What to Do
Since symptoms of Armillaria root rot generally don’t appear until the tree has already been infected (it can take as long as one to three years), it is generally impossible to save the plant. In this case you should remove the infected plant, including the roots. If you would like to replant in the area, be sure to choose a plant that is resistant to the fungus, as Armillaria can continue to live in the soil.
If the Armillaria-infected plant is one shrub in a row of shrubs, replacing it may be tricky. While many gardeners would like to simply replace it with the same kind of plant, it increases the chance that the new plant will become infected. And you may find that the other plants in that area are affected by the fungus later on. It's a tough choice: you can replace that one plant with something new that matches what you had or something that stands out as a sort of statement planting, and risk re-infection, or you could pull out all the potentially infected shrubs, a costly and possibly over-zealous reaction to the situation.
If you find yourself having to replace a plant that has fallen victim to Armillaria, don’t fret; there are resistant plant options. Plants that are resistant include: American holly, bald cypress, bayberry, black cherry, box elder, boxwood, common persimmon, crapemyrtle, dahoon holly, hackberry, Kadota fig, jacaranda, mission fig, mulberry, pawpaw, Southern magnolia, Southern red maple, sugar maple, sweetgum, and sycamore.