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Prepare for a giant bark aphid infestation

Thanks to a GardenLine listener, we now have new pictures of what giant bark aphids look like.

Photo: GardenLine listener

I give the listener credit for a great question, too … “Just checking to see if these are beneficial or not, and if not, should I nuke ‘em?”

Okay, I made up the “nuke em” part, but they certainly aren’t beneficial in any way I’ve ever seen. So, if you see this kind of infestation up and down the trunk or along the limbs of any of your trees, let’s definitely waste ‘em!

But before we get to the killing spree, here are some things to know about giant bark aphids.

First, don’t confuse them with bark lice, which are assuredly beneficial insects. Bark aphids are anything but beneficial, and they rain “honeydew” on everything below. Then, a black sooty mold develops on the honeydew. Most calls I receive about them seem to be from listeners wondering why their tree is dripping “sap,” or about the unusual bugs clustering on the tree.

I thought we were on the verge of having an infestation last summer, but we’ve escaped one for the past two years. And that has me a bit concerned for 2021, because these critters are cyclical and don’t appear in large numbers every year. Frankly, I think we are well overdue. And based on the number of pictures I’ve received in emails over the past week, I’d say the time is now.

There are a couple ways to combat the problem. First, you can blast them off with a water hose and treat the tree trunk a day or two later with dormant oil spray. Or, for an immediate kill, go with malathion, bifenthrin or any synthetic pyrethroid like the newly famous Cyonara Lawn & Garden, which is made from lambda-cyholothrin.

If you go with a dormant oil spray, remember to only spray the trunk or bark, because we are WAY PAST the dormant season. My previous advice during non-dormant months is to respray a week or two later, to be sure you kill any eggs or nymphs that may have been protected during the first application. Just be sure not to get any dormant oil on the leaves of any tree in the summer months.

And, finally, here’s a thought for manic organics who don’t want to spray anything. If the honeydew drip isn’t harming anything, entomologists say giant bark aphids are short-lived and will just disappear on their own.


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