What is wrong with my dahlia?

[SpacePotato]

First time I've grown dahlias, from tubas. They started really well. Looked nice and healthy then this happened. I'm assuming a pest got to it but can't see anything specific. Should I cut the top bit off?
Will it still flower? Help! Thanks.

Pics

I think I see green flies on the plant (aphids)- nasty buggers are running rampant this year.

Would that make the leaves brown like that? The damage was already there as the top leaves opened out.

They look a bit scorched, so frost/wind/sun on wet leaves could all have caused this.
I would leave it alone, but if it doesn’t seem to be growing properly at that point you can pinch out that main shoot.