Giant bark aphids … friend or foe?

Thanks to a GardenLine listener, we now have two new pictures of giant bark aphids. I give her credit for a great question, as well … “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 are not beneficial in any way I’ve ever seen. So, if you spot this kind of infestation up and down any tree trunk or limbs at your place, I say waste ‘em!

But before we get to the killing spree, there are some things to know about giant bark aphids. First, don’t confuse them with bark lice, which assuredly are beneficial insects. Many GardenLine callers have confirmed, though, that bark aphids are anything but beneficial - they rain honeydew (aphid excrement) on everything below. Then, a black, sooty mold develops on the honeydew. Most callers seem wonder why their tree is dripping “sap” or what are the unusual bugs clustering on trunks and limbs.

I thought we were on the verge of an infestation last summer, but it really never proliferated. And that’s why I’m a bit concerned for 2020 - these critters are cyclical and don’t show up as big infestations every year. Frankly, I think we are overdue.

There are a couple of ways to get rid of them. First, you can blast them off with a water hose and treat the tree a day or two later with dormant oil spray. If you want an immediate kill, go with malathion, bifenthrin or any synthetic pyrethroid. Even then, though, I’d suggest a dormant oil spray a week later to kill any eggs or nymphs that may have been protected during the insecticide spray. But here’s a note of caution: dormant oil CANNOT or SHOULD NOT be sprayed on any leaves of any tree in the summer months.

And here's something else to consider. If the honeydew is dripping harmlessly on nothing important below, giant bark aphids are short-lived and will go away on their own.

IMAGES: GardenLine listener

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