Requiem for Cherished Crape Myrtles – updated 2-2021

OUCH! Say “G’bye” to one of the South’s most cherished landscape trees. 

“You’re not gonna like any of this.”

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 Charlesto (see last photo). I don’t even have a problem with their being pollarded, which in Japan is a form of topiary called “fist pruning” (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 moot points 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.

SPOILER: YOU’RE NOT GONNA LIKE ANY OF THIS 

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, 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,  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 other plants. Only MUCH worse.

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. Again, much worse than sooty mold from aphids.

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’s temporary – because all the scale cannot be removed entirely from small twigs, they will simply come back the following year.

Of course, as Texas A&M 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 experienced experts are confident that the insects probably won’t kill healthy trees, the condition seriously weakens plants and usually spoils the flowers. And it’s permanent and terrible looking.

WHAT TO DO – OR NOT

Keep in mind none of the following – which I update every year – is merely my personal opinion, it is a professional report based entirely on what earnest 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 in mid-to-late summer or fall has very little if any effect.
• These treatments usually don’t give 100% scale control even if used every. single. year.

*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. While in some cases ladybeetles can eat a lot of scale late in the season, they aren’t really effective… and the soil drenches kill them, too.

Imidacloprid is the active ingredient in the most commonly recommended brands

Note the first and last lines of this photo I took from the label

**The active ingredient in soil drenches is absorbed by mulches and cannot get to roots, so apply them to clear soil to avoid wasting their effectiveness.

AVOID SCAMS

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, at least not for long. AVOID pest control or garden center sales  staff offering dishonest services or products outside these tried-and-true recommendations.

GOOD LUCK

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 front of a six-by-eight-foot picture window, and replaced it with a substitute (weeping yaupon holly) 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 or natural predators, just temporary measures that include scrubbing, spraying dormant oil in the winter, and using powerful, environmentally-harmful 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 (the latest from MSU; nothing has really changed since it was published)

ALTERNATIVE PLANTS

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.