If they are mostly broadleaf weeds, I'd wait until you have rain in the forecast and simply mow. Mowing will control many broadleaf weeds. It doesn't control grasses. There are particular broadleaf weeds not controlled by mowing, but you really should understand what they are before choosing a herbicide.
Here are my thoughts for what they are worth:
Frost seeding can be an effective way to overseed thinned areas of an established clover field (at about 1/2 rate as folks suggest), but I don't find it very effective at establishing clover in areas where weeds are an issue. You end up spending more time and effort fighting weeds over the life of the clover field than you would starting over.
Clover is best planted in late summer or early fall when rain is in the forecast. It should be planted with a cereal grain nurse crop. I much prefer winter rye. The cereal becomes the attractant that first fall, not the clover in most cases. It will usually germinate, but not put on much if any growth. The next spring, the clover and winter rye are much favored by weather over most weeds. The Winter Rye takes up space and shades out weeds from getting a foot hold. Winter Rye in particular has a chemical effect suppressing weed germination as well. The Winter Rye will dominate in the spring. The perennial clover is spending most of it's energy putting down a root system. Each time the Winter Rye gets a foot or so tall, mow it back to 6"-8". This will release the clover giving it light without killing the Winter Rye. By now, the winter rye has no significant food value for deer, but that is not the purpose. Deer have plenty of other native foods at this time of year. The purpose of the Winter rye is to protect the clover from weed infiltration during establishment. By summer the winter rye will die naturally on it's own. The clover will fill in as the winter rye dies.
Depending on your location and water conditions, the clover my go dormant in the summer. Ladino goes dormant during the summer in my location, but Durana usually does not. On very dry years, the Durana may go dormant for a couple weeks at most. When the fall rains and cool evenings come they favor the clover and it will really take off.
While I like to use these best practices to establish a weed free clover field to begin, I've learned to be quite weed tolerant when it comes to established clover. There are a few problematic weeds, but for the most part, after clover is established, I simply mow once or twice a year. Weeds don't bother the deer and some broadleaf weeds are favored by deer over clover and are more nutritious. When I start with a weed free field, I get 7 to 10 years out of a durana field before weeds become a big enough issue to deal with. And, at some point, the clover will have banked enough N that it is very hard to keep grasses out. Then it becomes time to rotate into an N seeking crop for a growing season or two before rotating back to clover.
Thanks,
Jack
