Elena Ive also taken a deep dive on he subject and can report that covering the ground does work for new beds, but not with underplantings. I almost eliminated it by covering everything with landscape fabric. Not the most attractive, but it worked as I dont have many underplantings.
I agree with what Mike has written, but there is one more chemical that works and is backed by research. The duration of the persistence of imildiproclide is ratio dependent so can be timed to avoid Spring flowering. There is another chemical backed by research... let me look up the name in my notes if youd like me to. Ive spoken at length to some of the researchers at OU and have taken much of their advice except where some insecticides are concerned.
An old remedy is tobacco spray, smoke and dead stalks which were used in greenhouses and as a mulch. The spray works great and is not systemic, but will infiltrate the leaf node enough to kill. Obviously spray when no pollinators are around. This needs to be done for at least a full cycle on a daily basis as one doesnt know when the midge will pupate. They do it faster the warmer the weather with cycles as fast as 3 days, so the damage grows exponentially.
Having said this, the most effective thing Ive done is avoid bringing it into my yard in the first place which is why I recommend isolating new plants on a hard surface, and surrounding the soil with Landscape fabric or paper, drenching them with a proper insecticide and keeping them from blooming for a while. This is easily done for new plants. While I dont worry as much about bare root since there isnt any soil, I have read that they can overwinter in the stems. Not sure about that, but I do now plant them in 5 gal. buckets first and isolate. as best I can. Its hard to change the soil on delicate bands and quarts so this is what I do.
