I used nematodes for this problem few years ago and it seemed to work pretty good. I also used predatory mites in conjunction so I can’t say which did the trick but I felt like the mites may have had better mobility and they were cheaper too. It was a specific species of mite which I don’t recall the name of atm.
I actually bred the nematodes in Petri dishes and grubs for a couple generations so I applied them a few times that summer, wasn’t able to maintain them though so I’ll have to buy them again I guess. After a couple seasons of no treatment I’m guessing that I will find quite a few root aphids again this potting season. I just got my hands on an entomopathic fungi culture to try out this year too, that’ll be fun to try. I don’t even know if it works against root aphids actually, maybe I can research a bit first. But it would be very easy for me to grow it out and apply it anyways.
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