What’s a Root Aphid and What’s Mycorrhiza?
It’s not easy to tell the difference between them. Aphids are detrimental and Mycorrhiza are beneficial, so we have to get this right. Which is tricky, as they are doppelgängers.
I’ve seen lost branches from root aphids, and general weakening. They are usually found in greatest numbers right next to the pot wall. Mycorrhiza helps uptake of nutrients and water. Also easy to see next to the pot wall.
The following photos show a root mass of a Scots Pine we repotted last week. It shows BOTH Mycorrhiza and root aphids. And this is where it gets tricky.
A Scots Pine root mass. Old hands at bonsai will say, “Yup, that’s Mycorrhiza.” And you’d be correct. The milky, soft-looking, off-white patches are outlined in red.
This side of the root ball also has Mycorrhiza, but if you looked quickly, you’d think it was all fungus. But only that outlined in red is Mycorrhiza. The rest—the bright white patches—are root aphids.
This side also has mostly root aphids, with just a little Mycorrhiza showing—the tan colored patch outlined in red. Root aphids are known by their spotty white, mealy rather than webby, growths. The aphids themselves are almost impossible to see in the root mass.
This shot shows two root aphids on the pot wall, cream-colored ovoid things, in the middle of the photo. Even with a 10x loupe these can be hard to see. (There are many root aphid species, and some don’t make the white poofs we see in the soil.)
Root aphids aren’t easy to ID. But if you do find them, consider control, or risk a weakened plant.
A systemic pesticidal drench is a start, like Safari or Bayer. Some have used drenches of pyrethrins, oils, and Zerotol. Beneficial nematodes may also offer control.
Multiple applications of controls may be required as root aphids are NOT easy to eradicate. (In one text exchange a friend had “root” autocorrected as “rude”, which felt accurate.)
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I’ve wondered about the little white spots, root aphid or Mycorrhiza for a long time. Thanks for the ID and the solution. My Bald Cypress exhibit both and now I will attack the little buggers! Thanks very much for this timely topic.
Great Post Michael! I’ll be on the look out for these little nasties henceforth!
If this is discovered while repotting a conifer, is it okay to drench the root ball even though there may be some risk of washing away beneficial mycorrhiza? Would it be advisable to follow a different process to treat the aphids?
Hi, thanks for the question! No worries about washing away Mychorriza, it’s hard to kill even with a fungicide. Watering our plants won’t affect it, and washing the root ball won’t do anything. If you have too much a Daconil fungicide drench will knock it back, but won’t kill it. Can clear up drain holes though. As for the aphids, that’s going to be a different chemical. You need a pesticide—-we’ve used Safari. Many pesticides might beat back root aphids.