crape myrtle mold-like growth on bark?

Asked September 25, 2020, 4:02 PM EDT

Hi, I noticed some gray-greenish spots on the bark of our crape myrtle-- they smudged when I touched (see especially the right side of the attached picture). I thought mold usually attacks the leaves so I wasn't sure if this was lichen or something else, and whether it was harmful or not. Can you tell me what if anything I should do? thanks very much!

Montgomery County Maryland

3 Responses

Though this does look like a type of mold/fungus, it is not a leaf pathogen, as you suggest. It also doesn't look like lichen. We do not recognize this organism as being common or problematic on crepemyrtle in particular, and may be superficial and not of concern. It does somewhat resemble the early stages of the fungus Green Stain Mushroom (https://www.marylandbiodiversity.com/view/12319); if so, this organism grows on dead or dying wood, but isn't necessarily the cause of the dieback itself. If the growth at the end of this trunk/branch looks normal, that we would not be concerned at this point. That said, the slightly cracked appearance of this trunk is suspicious; keep an eye on it going forward. (Even if it is a wood-decay fungus, there is nothing that could be done except to remove that wood, which is a drastic measure to take at this point.)

For now, simply monitor the wood in this area and see if more extensive mold development appears and if any dieback seems to be occurring on this corresponding region of the canopy. (Dieback will be more prominent in spring and early summer, as opposed to now when leaves are getting ready to fall.) Otherwise, no treatments are needed and the crepemyrtle will probably be fine long-term. Minimize the plant's stress by watering well when needed; crepemyrtle are drought-tolerant but would prefer to not experience drought at all if possible, as this makes any plant more vulnerable to damage from other organisms taking advantage of their stressed condition. Here is general watering advice for trees and shrubs, if useful: https://extension.umd.edu/hgic/topics/watering-trees-and-shrubs

Miri

thanks (you can see the collar in the top left where I took out a cross-branch which had been rubbing on the trunk with the mold, but I thought the trunk had recovered pretty well and it doesn't really look like the same spot, but I'll keep an eye on things).