I have about 6 acres of pasture with 4 horses, and like others, I mow and drag. I also pull the flowering weeds by hand. I have an armful of weeds every time I walk through the pasture.
It is important to set up a routine. Here's what I do...
1. I use temporary fencing so I can get my horses off the pasture for short periods.
2. Fertilize in spring. Fertilizer will help the grasses outcompete the weeds.
3. I harrow the manure weekly when there is no snow. We use a diamond harrow as well as a chain link gate.
4. Mow when plant get over about 8" high. Mow to about 4-6". I always follow mowing with harrowing.
5. I plan to overseed with a horseman's pasture mix either this fall or early in the spring when I take the horses off the field and keep them in the sacrifice area.
6. Rotational grazing forces the horses to eat the pasture down more evenly and makes managing manure easier because it is confined to a smaller area.
7. I try not to use pesticides, but if the above methods don't control the weeds, we do spot spray trouble areas.