Thanks to a GardenLine listener, we now have a new picture of what Giant Bark Aphids look like; I give the listener credit for the question she asked 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 aren’t beneficial in any way I’ve ever seen. So, if you see this kind of infestation up and down the trunk and limbs of any of your trees, then I say let’s definitely waste ‘em!!!
But before we get to the killing spree, here’s some things you need to know about the Giant Bark Aphid. First, they are not to be confused with bark lice, which assuredly are beneficial insects. As most of the calls the radio program have confirmed, bark aphids are anything but beneficial … they rain honeydew on everything below. Then a black, sooty mold develops on the honeydew. Most calls seem to be from listeners either wondering why the tree seems to be dripping sap (actually the honeydew excrement from the aphid) or “what’s the unusual bug clustering on my tree trunks/limbs?”.
These critters are cyclical and as such don’t do big infestations every year. There are a couple ways to rid yourself of the problem. First, blast them off with a water hose and treat the tree trunk a day or two later with dormant oil spray. If you want an immediate kill, go with Malathion, Bifenthrin or any synthetic pyrethroid like the newly famous Cyonara, which technically is made of one of those synthetic pyrethroids known as Lambda-Cyholothrin.
Also, when I suggest Dormant Oil Sprays, just remember that I’m only asking you spray the trunks/bark, because we are WAY PAST the Dormant Season, eh?! My advice in the past during non-dormant months, is also to re-apply such a dormant oil spray a week or two after the insecticide kill, to insure you kill any eggs or nymphs that may have been protected during the insecticidal spray. But a dormant oil spray CANNOT or SHOULD NOT be sprayed on any leaves of any tree in the summer months.
Here’s also a fun thought, if you’re manic-organic enough that you don’t want to spray anything; if the honeydew is dripping harmlessly on nothing below, entomologists say they are a short-lived insect that will go away on its own.