Rushing: We have a real problem with insects in the garden

By FELDER RUSHING GUEST COLUMNIST,

Forget the snooty debates over “crape murder” pruning; it’s a moot point now. We got a real problem.

In my lifetime, a fast-spreading insect wiped out most of America’s elm trees, and a leafspot disease ruined millions of red Photinias. And nothing we threw at either helped much at all. 

Many if not most of those trees are long gone, though a few here and there survive, and a few newly planted ones are far enough apart to be less likely to get attacked. 

Sadly, in just four or five years a similar situation has reared its head in the Magnolia State that is overwhelming beloved crape myrtles.

I wrote about it last year, but am seeing it in more places and getting worse, with little relief in sight.

Called crape myrtle bark scale, the tiny legless white or grayish bugs with insecticide-resistant waxy shells quickly cover twigs, branches, and trunks of trees, usually a few at first but quickly avalanching into crusty masses.

As they feed, they produce a sticky, plant sugary excrement, just like the stuff aphids drip from undersides of leaves of oaks, hackberries, gardenias, and a few other plants. That rain dripping from your trees is bug excrement. 

That’s bad enough, but a distinctive black “sooty mold” quickly develops on the drippings, covering everything underneath in black (including my grandmother’s concrete chicken).

Other than how it shades leaves which can weaken plants, the sooty mold in itself is harmless. But it has long been a big frustration, because there is no way to prevent aphids and mites from attacking plants, and it’s not practical to spray for them. The mold scrubs off with soapy water, or eventually flakes off over winter, but meanwhile it’s a really unsightly, sticky mess.

However, an infestation of crape myrtle scale, which may not kill your tree but it’s usually too much to bear, dumps their stuff all over, and the sooty mold often turns the entire trees, trunks and all, and even the ground underneath, black.

Here’s the bad part. From Texas to the Carolinas, the top nonprofit and university experts are saying that treating for bark scale successfully may not be possible, even if you use carefully timed pesticides. Some have tried spraying a horticultural oil in late fall or winter to smother overwintering nymphs, or scrubbing the scale off with a soft brush or low-pressure washer.

But the current best hope being held out is soaking the ground underneath plants with a powerful “systemic” insecticide in March, April, May, or June, which is when the insecticide is best absorbed into trees.

All the experts, including those at MSU, report that treating in the summer or early fall is much less effective. And that, like spraying for mosquitoes, the recurring problem will likely just return quickly.

So, the treatment, using “neonicontinoid” pesticides that are banned in Europe because of how they affect bees, is expensive and has to be repeated, and then with little chance of it working for good.

This is a real heartbreak to folks, including myself, who’ve invested years in the statuesque trees just to watch them peter out as they reach their peak of beauty and usefulness.

But all over the South we’re working hard to find a solution to the bark scale. Fingers crossed, but meanwhile, if you want to see good photographs of the insect on crape myrtles, plus the latest recommendations of what to do when (including a link to MSU’s latest 2019 report), go to my blog on it at www.felderrushing.blog.

It includes list of what we can plant next.

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