Tree-killing flies?

[biwa]

Last Spring I planted a plum tree and a beech tree and they both died. They happened to be covered in flies when they died. I thought it was just a coincidence.

This Spring I replaced them with another plum tree and another beech tree. The plum tree had some transplant shock because I planted while it wasn't dormant, but the beech tree was dormant during the transplant and was doing well for a few weeks afterward.

Now suddenly the beech tree is covered in flies and its leaves are drying up and turning brown. The plum tree has one fly on it and has lost about 1/3 of its leaves since yesterday. The plum tree can be explained by the poor transplant, but the beech tree was doing really well until these flies showed up. I think that in the beech tree's case at least, the flies are the cause of the problem.

Last year when I asked about this, someone told me they were "seedcorn maggots." I'm not sure if that's true or not, but even if they are seedcorn maggots, I don't know how to get rid of them.

I don't want to lose these two trees. Please advise me on how to get rid of the flies so the trees won't die.

EDIT: A unique feature about the flies that may help to identify them: Most of the flies are dead. They attach themselves to the plant via something coming off their face (maybe snout, tongue, or some kind of mouthpiece). The few that are alive stand on the plant like normal, or stand on the corpse of one of the dead flies.

[Kisal]

I have not found that the seed corn fly feeds on trees, but here is link to a page of information about it. I suggest that you take one of the dead flies to your Extension Service office for an exact identification. They will also be able to provide information about necessary controls to use.

[url=https://entoplp.okstate.edu/ddd/insects/seedcornmaggot.htm]Seed Corn Maggot, Delia platura[/url]

[url=https://www.extento.hawaii.edu/kbase/Crop/Type/delia_p.htm]Delia platura (Meigen)[/url]