From the Vine – Root Rot
Fall is the time to rake leaves, tidy up the yard, and put gardens to rest. While you are out completing these chores, you should keep your eyes open for honey mushrooms. Honey mushrooms appear in the fall and grow in clusters in size from tennis balls to basketballs. They are honey colored and grow near the base of trees and shrubs or where old stumps use to live. They are the number one indicator of Armillaria root rot in the landscape, so if you see them, you have trouble.
Armillaria root rot has also been called oak root rot, but it infects many species of trees and shrubs including oaks, maples, azaleas, beeches, birches, boxwoods, cedars, dogwoods, firs, poplars, rhododendrons, yews, roses, and others. It also will infect and kill fruit trees in the landscape or orchards.
Armillaria is typically a problem in older plants or plants that have been stressed due to drought, frost, insect attack, mechanical injuries, poor drainage, low soil fertility, excessive shade, or pollution damage. However, it can be an aggressive pathogen under some conditions. Older or mature plants can withstand infections for several years, resulting in a slow decline, eventually ending with the death of the plant. Above-ground symptoms include leaf drop, dieback, and an overall decline in plant vigor. On conifers, the crowns of infected plants start to thin and change colors, often turning red, brown, or yellowish. Conifer infections sometimes result in heavy resin flow at the tree base. Usually, homeowners do not notice Armillaria root rot until the plant is dead or dying. No control is possible at this point and the plant should be removed.
Replanting can be problematic because Armillaria can survive for many years as rhizomorphs in soil or in old wood and stumps. Remove the affected plant and thoroughly dig up and remove all large roots, stumps and any other wood or prunings from the affected area. When planting in areas where a plant has died, or where trees have been removed, as in new construction, remove all old roots, stumps, and wood before replanting. Consider planting ornamental herbaceous or perennial plants or grasses in the area for a few years before attempting to replant woody species.
Healthy trees and shrubs are better able to resist Armillaria root rot than stressed plants. Choose species that are well-adapted to your region and growing site. Maintain their health by fertilizing as recommended, watering during dry spells, and improving drainage in wet areas. When possible, prevent defoliation from insects and foliar diseases. Be careful to avoid damage to roots when digging or tilling. Do not push up soil around tree trunks and do not move soil from affected areas into sites where woody species are growing.