There is only one way to get rid of Gall Midge: As soon as you see an infected bud, pull it off and throw it in your household garbage. Small flies lay eggs in early spring on daylilies, especially yellow ones. They develop into the grubs which then fall to the ground and hid in the dirt until next spring. If you don't have a reblooming type daylily, you never get the flowers. If you keep destroying all infected buds as soon as they show signs of being infected, you will be able to start to control the problem.
The other solution is to replace them with mid to late season openers which form buds after the egg laying period is over (go to the members tab and find Simbad - send her a private message and she should be able to tell you which ones form buds after the egg laying period). I have a plastic bottle in my main area that I put any distorted bud in, and then throw it away when it is full.

I have the same trouble with the early flowering type but picking the swollen heads off is best and throw in the bin, it will reduce the amount of flowers but the following year you will notice the difference

Hi, welcome to GoY, I agree with Wylie, there is no insecticie currently available, that lists Hemerocallis gall midge as being treatable, but the RHS, has done some research, and insecticides based on thiacloprid, or
acetamaprid, eg, 'bug clear ultra' or bayer provado ultimate bug killer, applied as per the instructions in june can reduce,[but not eliminate] infestations, but don't spray insecticie onto open flowers, due to the risk to pollinating insects, the risk of these is usually over by mid july, so you could, as Wylie suggests, grow later flowering species, or cultivars, Derek.

Gall midge is untreatable because the larvae develop inside the bud and are protected from contact with an insecticide. If you wait for the bud to open, it is too late and they would have already dropped to the ground.

Thank you all for your replies. I will dig up the diseased plants and plant the out of the way, then pick of the buds when they appear. Would it be unwise to plant any other kind of lily in the same spot to replace these? I have clay soil.

Hi, the plants are not diseased, they're just under attack from the Hemerocallis gall midge, or to give it it's sunday name, contarinia quinquenotata, so there's no need to worry about replanting anything else in the same spot, Derek.

And Hemerocallis are not related to Lilies either.
We have given up on them, no matter how hard we tried to remove all the infected buds, the insects still managed to spread to all our plants, early and late and all colours. We have virtually none of them left in the garden now. Dug up and replaced with other things.
I would also say that Hemerocallis are also the worst plants we have ever grown for being attractive to Couch grass too!