OUCH! Say “G’bye” to one of the South’s most cherished landscape trees.
In spite of their maybe being a tad overplanted, I love crape myrtles – the lilac of the South. I even made the trek to South Carolina to hug the oldest crape myrtle in North America, planted in 1786 by André Michaux at Middleton Place near Charleston. I don’t even have a problem with their being pollarded (what some folks call “crape murder”), especially when gardeners like me weave the trimmings into wattle fences. For more insight on this check this blog post out.
TROUBLE IN EDEN
But just like whether to spell it “crape” or “crepe” or want to argue about pruning, they’re all moots point now, water under the bridge, as our beloved crape myrtles are being pushed out of the garden entirely by a new pest that is for all practical purposes uncontrollable. Get used to it.
This blog is about what the problem is, and what we can – or can’t – do about it.
The invasive Asian insect called “crape myrtle bark scale” first showed up in the US around 2006 but has been spread far and wide, partly via infested trees being sent to garden centers, then to gardens, then from tree to tree. It’s now beyond practical control.
Individual scale are just tiny things, not much bigger than fleck of ash, but they multiply and spread rapidly, all but overtaking trees in one or two seasons and rendering them basically unfit for landscapes.
The tiny legless white or grayish bugs hatch from eggs and crawl as nymphs onto twigs, branches, and trunks of crape myrtle trees, which attach themselves, sorta like little plant ticks, and cover themselves with a spray-resistant waxy shell.
They can quickly cover entire trees in crusty masses, and as they suck sap they exude a sticky, plant sugary excrement, just like the stuff aphids and mites drip from undersides of leaves of crape myrtles, oaks, hackberries, gardenias, and a few other plants.
A distinctive black “sooty mold” quickly develops on the drippings, which turns everything below the insects – leaves, limbs, trunks, other shrubs, garden furniture, even plastic flamingos and mulch – as dark as night.
The mold itself will flake off over the winter, or can be scrubbed off with a soft brush and soapy water, or can be washed off with a pressure sprayer using LOW pressure to avoid damaging thin bark. But it will come back the following year once the scale insects crank back up.
Of course, as Texas horticulturist Greg Grant mused recently on my NPR program, with the naturally-dark foliage crape myrtles such as ‘Black Diamond’ being so trendy, “maybe scale-infested trees will be accepted as well…”
Though seasoned experts are confident that the insects probably won’t kill healthy trees, the condition weakens plants. And it’s permanent and terrible looking.
WHAT TO DO – OR NOT
Keep in mind none of the following is merely my personal opinion, it is a professional report based entirely on what seasoned university and other nonprofit insect specialists from Texas to the Carolinas – including the Crape Myrtle Society of America – have convinced me to be the only proven recommendations for treating infested trees:
- The insect is not likely to kill healthy trees, just weaken them and turn them black
- Clean off what you can reach with a soft brush or low-pressure washer (to avoid damaging thin bark)
- Liquid insecticide sprays have practically no effect on mature scale and won’t control the problem by themselves; don’t waste time and money on useless sprays!
- Spray dormant oil in December-February (after leaves shed in the fall and/or before spring bud break) to smother many of the overwintering scale insects
- The main control recommendation is to use a soil drench – lots of water mixed with a systemic insecticide (*see below) applied to bare (not mulched) soil directly underneath infested trees in late March, April, May, or June. Though some licensed landscape pest managers may pressure-inject root zones up to September in wet years, applying drenches later in mid-to-late summer or fall has very little if any effect and is NOT recommended.
*Most of the currently-recommended systemic insecticides contain imidacloprid which is a long-lasting, distinctly non-organic systemic “neonicotinoid” product that has been banned across Europe for its serious effects on honeybees and other pollinators even weeks after application, and can kill beneficial insects that feed on poisoned pests.
Scroll over these images for a little more detail:
And these treatments still won’t give 100% scale control even if used every. single. year.
Be aware that all but the most principled pesticide salespeople will earnestly cater to your frustrations and fears to make a sale – any time of the year – and well-meaning neighbors will tell tall tales of home remedies that simply do not work. AVOID pest control or garden center sales staff offering services or products outside these tried-and-true recommendations.
Sorry, friends… but I have several large crape myrtles in my own garden, as do professional horticulturist friends in the public and historic gardens under their care. And we’re all in the same boat, all on the same sad page. So we just do what we can.
In fact, in early 2019 I dug up a strategic crape myrtle I had planted and carefully pruned in from of a six-by-eight-foot picture window, and replaced it with a substitute that won’t drive me bonkers for years to come.
To sum up – and keep in mind again that none of this is my personal opinion, it is what honest, nonprofit experts agree on: Crape myrtle bark scale is serious and here to stay, and there is no long lasting control, just temporary measures that include scrubbing, spraying dormant oil in the winter, and using strong systemic soil drenches in the spring.
We’re learning to live with it, or treat it as best we can for as long as we can, or remove and replace ours with something else.
For an official summary of this pest – keeping in mind that that university researchers tend to paint “best case” scenarios based on possibilities rather than coming across as negative or unhelpful – here is the MSU Extension Service publication on this serious pest. Note that they admit that no control is 100 percent effective, meaning it won’t work in the long run. Click here for the 2019 MSU update
Though there isn’t an ideal substitute for this otherwise amazing plant, there is a pretty great selection of pretty decent alternatives that can be used for very similar landscape effects. The following small trees or large shrubs can grow “as is” or be “limbed up” into multiple-trunk accent plants:
Japanese maples, hollies (Burford, yaupon, Foster, Nellie Stevens), Vitex, windmill palm, Siberian/Drake elm, Cleyera, wax Ligustrum, Pyracantha, ornamental pears, Japanese persimmon, Camellia sasanqua, purple leaf plum, redbud, Chinese parasol (Firmiana), Ginkgo, wax myrtle, althaea (rose of Sharon), fringe tree (grancy graybeard, Chionanthus), arborvitae, silver bell (Halesia), smooth sumac, cherry laurel, Magnolia ‘Little Gem’, sweet bay Magnolia, red buckeye, and parsley hawthorn.
If you have others, lease share their names in the comment section below!
Yeah, I know some of these are strongly disliked by some gardeners, or have minor weaknesses and seasonal imperfections, or can be seriously invasive and therefore not on everyone’s recommended list… But I’m not here to make value calls, just throwing out a few ideas that may help ease our loss.
Some of these can be planted while still small underneath or between crape myrtles, to give them time to get some size on them if/before the old crapes need removing.
In some situations, vine-covered arbor posts can substitutes – quickly and pretty inexpensively. And why wait? I’ve already set several between my crape myrtles to get a head start on the day when the trees will have to be removed.
So sad about this situation, but glad to get this unhappy news off my chest. But I am so thankful to have had a chance to give the oldest around an appreciative squeeze.