I would say not, I use a bit of garden fleece just to keep the birds off. That lets light and water through so that the seeds can germinate and grow. Black plastic would prevent both light and water from getting through.

Hi, if you're preparing the ground right, and creating a good 'tilth', and raking over lightly to just cover the seed, it should germinate, the usual reason for it not too, is birds, I have in the past put black polythene over newly sown seed, just wet the ground first, sow the seed but don't rake it in, cover with the plastic, and put some bricks on the edges to stop it blowing away, allow 4 or 5 days, and see if it's germinated, if it has remove the plastic, if not, and the soil has dried out, give the soil a light watering and recover, check every day to see if there's any sign of germination, if there'e no sign after about 2 weeks, then I would think there is likely to be a problem with your seed, Derek

Agree with Derek, but would add, I think the 'preparing a tilth' might be the step you've omitted, since you've not mentioned it. Its necessary to rake or fork up the top couple of inches of soil on the bare patch, and get a fine tilth (like fine crumbs) tamp it down to level it, usually with the back of a rake, then broadcast the seed on top, using twice as much as you need so the birds can take some, because they will if you're not covering it. I have put plastic over the top to speed germination earlier in the year before, but clear, not black, and this time of year, the sun's strong so probably not a good idea to use plastic at all. Keep the seed bed moist and if you do use plastic, check every day whether its germinated or not.

Have you treated the lawn previously with herbicide? Roundup or something like that? It may still be present in the soil and preventing seeds from germinating? What caused the brown patches in the first place? Try replacing the affected soil with new top soil, then reseed. The birds will eat a few seeds but will leave you plenty to germinate.

Bathgate makes a good point - if you used a lawn weed, feed and mosskiller preparation previously, you need to wait 6 weeks before attempting to re-seed any bald patches.

many thanks to all who answered my query
the comments were very helpful thank you