Sick Crepe Myrtle - How to save?

Asked October 26, 2020, 2:51 PM EDT

Last summer, I noticed that a couple branches of my crepe myrtle had little to no growth on them. Around the same time, the folks that treat my lawn for weeds (TruGreen) mentioned it as well and offered to begin treating my shrubs and trees to control diseases and insects. I took them up on the offer in hopes that it would help the tree. This summer, there continued to be very little growth and this weekend mushrooms begam growing on and around the tree. It may be important to note that was planted around 10 years ago to replace a large tree (not sure what kind) that died in this spot. Upon building the house, we designed the driveway around the tree that was there to avoid having to remove it - the thinking was that perhaps we ended up covering too many of the roots as the tree ended up dying over the next few years. I would really like to do whatever I can to save this tree and have included some pictures in the hopes that you may be able to provide some advice as to what may be going on. Much appreciated!!

New Hanover County North Carolina

1 Response

I am sorry to report that your tree has a disease called Armillaria. Armillaria root rot is a disease of trees and woody plants, although it also affects palms, succulents, ferns, and other herbaceous plants. This disease is caused by fungi in the genus Armillaria, also known as “oak root fungus,” although the fungus has no specificity for oaks. Several species of Armillaria are known to occur in California, but Armillaria mellea is the species commonly found in home gardens, parks, vineyards, tree crops, and natural landscapes. This pathogen has a broad host range, potentially affecting thousands of ornamental and crop plants. Other species of Armillaria occur in forests, causing heart rot and acting as saprophytes.

The oak root fungus attacks and kills the vascular cambium (the tissue that generates bark and wood) in woody roots, then spreads laterally to the main stem, which can girdle the base of the trunk and kill the entire tree. Armillaria is also a white rot wood-decay fungus that destroys the strength of wood in roots and at the base of infected tree trunks, thereby increasing the likelihood of tree failure. This dual nature of Armillaria, both as a pathogen (killing the living tissues in a tree) and a saprobe (living on dead or non-functional wood after the infected host dies), presents a challenge to management because its inoculum (infective tissue or propagules) can persist for decades below ground as mycelium (vegetative fungal tissue) living in partially-decayed woody roots (residual roots) long after the infected host plants have died or were removed. There are no known cultivars or varieties of plants that are completely immune to Armillaria root rot, and some plant plants are very susceptible to the pathogen. For example, peach (Prunus persica and related Prunus hybrids) and Peruvian pepper (Schinus molle) are highly susceptible. Susceptible plants should not be planted in landscapes where trees have died from Armillaria root rot, especially when large dead roots may remain in the soil.

Reducing tree stress and ensuring good tree conditions are the principal beneficial practices in preventing rapid decline. Although A. mellea is considered highly virulent, most deaths of infected trees in landscapes can be attributed to excessive irrigation or other stresses.

Avoid physical damage to roots, soil compaction in the root zone, and addition of soil on top of the existing grade (especially during construction). Most importantly, prevent the waterlogging of soils around trees from excessive or inappropriate irrigation, especially in summer. Do not irrigate trees that are mature, established, and have never been irrigated. Excessive irrigation can be especially common for drought-adapted trees planted in lawns. In such cases, it is preferable to maintain a mulched turf-free zone out to the dripline of each tree, if possible, and allow the soil under the tree to dry out between irrigations.

There is nothing you can do once you have this pathogen.