Black (looks like honeydew) on crape myrtle - Ask Extension
I think this is one of the crape myrtle that came from the arborday foundation (it's hard to identify with all of the black on the leaves.
It is cov...
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Black (looks like honeydew) on crape myrtle #876943
Asked July 12, 2024, 10:14 AM EDT
I think this is one of the crape myrtle that came from the arborday foundation (it's hard to identify with all of the black on the leaves.
It is covered in a black substance that looks like it got Sprayed with tar.
It's currently wet from the rain and wipes off easily, so I may try hosing it off with some pressure.
I'm more concerned, however, with what it may be and what's causing it. It looks very much like honeydew from some insect, but they is nothing above it.
Just add I was talking the photos I noticed something on the underside of the leaves. (Third photo)
I'm confused and need your guidance.
Thanks again!
Jon
Harford County Maryland
Expert Response
Hello Jon,
Honeydew is clear and sticky (it's essentially sugar-water), but the black residue is sooty mold, a very common fungus that grows on the honeydew. (It does not infect the plant, just covers any surface which honeydew is coating.) The linked web page provides more information. A pressure spray of water should help dislodge some of it, or at least dilute the honeydew to speed-up the weathering-off of the sooty mold.
The insects on the leaf underside are Crapemyrtle Aphids. They are not a serious pest in terms of impacts to plant health, but when too numerous and contributing to a sooty mold outbreak, can be treated with low-toxicity insecticides. Bear in mind that insecticidal soap and horticultural oil, two of the most low-impact options, need to contact the pest thoroughly in order to be effective, so spraying the undersides of all the leaves on a short shrub may be difficult. (Even if you opt to blast them off with plain water from a hose instead, the same challenge of reaching them all remains.) It's okay if you don't eradicate them; a reduction in population should be enough, and natural predators like ladybugs should eventually find them and help suppress their numbers. Do not spray anything other than water if the temperatures are above 85 degrees, or plant tissue damage might result.
Miri
Honeydew is clear and sticky (it's essentially sugar-water), but the black residue is sooty mold, a very common fungus that grows on the honeydew. (It does not infect the plant, just covers any surface which honeydew is coating.) The linked web page provides more information. A pressure spray of water should help dislodge some of it, or at least dilute the honeydew to speed-up the weathering-off of the sooty mold.
The insects on the leaf underside are Crapemyrtle Aphids. They are not a serious pest in terms of impacts to plant health, but when too numerous and contributing to a sooty mold outbreak, can be treated with low-toxicity insecticides. Bear in mind that insecticidal soap and horticultural oil, two of the most low-impact options, need to contact the pest thoroughly in order to be effective, so spraying the undersides of all the leaves on a short shrub may be difficult. (Even if you opt to blast them off with plain water from a hose instead, the same challenge of reaching them all remains.) It's okay if you don't eradicate them; a reduction in population should be enough, and natural predators like ladybugs should eventually find them and help suppress their numbers. Do not spray anything other than water if the temperatures are above 85 degrees, or plant tissue damage might result.
Miri
