I reseeded a lawn with lots of bare patches after removing all the moss. By the time the new seed is just starting to grow, it's already getting infested with dandelions and dock leaf weeds which both grow quickly and quite large. I'm worried that by the time the grass is established, the weeds will have taken over and ruined all my work. What can I do?
If all you did to your mossy lawn was remove the moss, you may not get very good grass anyway - moss tends to thrive where the soil is acid and there's too much shade for grass, while weeds are far more adaptable than lawn grass.
My preferred approach would be to get a soils test, till the lawn area, plant a smother/green manure crop, till that in along with whatever amendments are needed per the soils test, retill at least twice to kill new weed sprouts (and possibly run another smother/green manure crop), re-till once or twice more and then sow.
I originally offered up my non-preferred approach of hitting it with a broadleaf weed killer, but the instructions state not to use on new grass.You could pull them, preferably before they go to seed.