cotton white ball on a crêpe myrtle leaf?

Question: What is this white cotton ball like infestation that is found on the top of a crêpe myrtle leaf? Many of the outer brim leaves of the crêpe myrtle have this problem. Last evening we sprayed the leaves with dish detergent and water and so most of the cotton balls are gone this morning. It looks something like an adelgain on a Norway, spruce.

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 27, 2023, 11:26 AM EDT
response: We can't see the residue clearly enough to make an ID. Are you able to send us more photos outside of a plastic bag and in better lighting? Common ailments for Crapemyrtle include powdery mildew (for which we've seen a few heavy outbreaks so far this year on some varieties) and, in recent years, Crapemyrtle Bark Scale. The latter insect would not be found on foliage (or very rarely), though, just on the bark of twigs, branches, and trunks.  A light infection of powdery mildew does not need treatment. Heavy outbreaks might benefit from either trimming off the most mildewed branch tips or treatment with a fungicide labeled for use on this particular disease. (Many products do treat powdery mildew.) Follow all label directions if you choose to spray, and be aware that fungicides may risk harm to pollinators (so do not treat flowers), don't always work successfully, and may have restrictions about being applied while temperatures are above 85 degrees.  Do not use a home remedy pesticide like dish soap or detergent; the linked page by Penn State Extension discusses why they can be hazardous to the plant and/or the environment, plus they also don't often work well. Even if such a treatment successfully suppressed some mildew in the short term, it is not going to effectively eradicate the infection and, like any topical pesticide application, would need repeat applications to maintain that disease suppression, which could damage the plant even if the first exposure did not.  Miri

responder: The Question Asker Replied July 27, 2023, 10:47 PM EDT
response: Miri,The sample I sent is very clearly showing the cotton like balls on the crêpe myrtle leaves. You say you can’t see because they’re in the bag but if you look again, they are are on top of a plastic bag. I can see the pictures as clearly  as if it were right in front of me and I wonder what you are seeing.Also, my email tells you that I used a little bit of dish detergent and water, and that it worked in wiping out a large amount of these cotton like nests on the top of the leaves.It seems like you are convinced it is a bark scale or a powdery mildew. I can tell you it is neither.  I told you it is like adelgin (spelling may be incorrect.) on a Norway Spruce. Finally, I do not see any harm in putting a small amount of liquid dish detergent in a spray bottle and spraying this on the leaves since it worked very well, and there is no danger in this spray damaging vegetation or in causing an infestation to spread. Don’t you think this is better than using lots of poisonous chemicals? As far as I know, this is something new in this area that is found on crêpe myrtles. I hoped you would take a look at it and tell me if I am correct.Thank you.On Thu, Jul 27, 2023 at 11:26 AM Ask Extension <<personal data hidden>> wrote:

responder: Answered by the Home and Garden Information Center (HGIC), University of Maryland Extension. For timely gardening information and tips, subscribe to our Maryland Grows blog and quarterly newsletter. Follow us on Facebook, Instagram, and YouTube. Replied July 28, 2023, 11:26 AM EDT
response: The symptoms pictured look closest to those produce by a powdery mildew infection, which is one of the only pests/diseases that would produce white residue on foliage. We do not see any indications of adelgids and they are not a pest of Crapemyrtle. While adelgids are very closely related to aphids, the aphids that infest Crapemyrtle do not have any white wax the way adelgids do. Some predatory lady beetle larvae consume scale, like Crapemyrtle Bark Scale, and happen to look very similar to them by having a fluffy white waxy body coating, but this is not left behind when they wander the plant to feed. You can see an example of their appearance in this blog article. Certain planthopper nymphs produce a fluffy white waxy body coating as well and this does get left behind as the nymphs run/jump around, but we do not see it on foliage -- stems instead -- and they are not a typical pest of Crapemyrtle. Even if present, they are not of concern and do not need treatment.  The surfactant nature of soaps and detergents will loosen or dissolve many substances not dissolvable in plain water (oils, waxes, etc.) so it's not surprising it worked to remove the substance pictured. If this is mildew, the spray might have killed part of the fungus, but it will not be able to cure infected foliage because part of the fungus is also growing inside the leaf, out of reach of surface sprays that are not designed to kill fungi. Surfactants can also remove the wax that coats plant leaves, so depending on dosage (both dilution concentration and how often leaves are repeatedly exposed), eventually this can lead to plant tissue damage. It's good that your prior spray had no ill affects so far, but that does not mean we encourage another treatment. Detergent is as much of a "chemical" as those manufactured for pesticide use, but at least the latter group are tested rigorously for environmental impact and plant safety whereas household products not intended for this use are not. Several pesticide ingredients are organic, derived from naturally-occurring plant oils, natural soap compounds, and organism extracts (like insect-affecting toxins made by soil bacteria) so are as low-risk as any pesticide gets.  For a second opinion you can always bring a physical sample of the symptom to a local Master Gardener plant clinic or your county Extension office if they have walk-in hours. Not all will have ready access to a microscope, but we doubt that will be needed in this case to make a diagnosis. Photos of the entire tree or showing how extensive the symptoms are on the canopy may help them make a diagnosis in combination with a physical sample (more than one leaf would also help).  Miri