Weed control in organic pastures takes an integrated approach. There is no one best practice to avoid or rid a pasture of weeds. Grazing management is the most important influence on weed populations. Pasture renovation is usually used to control major infestations of weeds or undesirable grass species. Growing an annual crop such as oats or annual ryegrass will help provide a general cleanup of the pasture before reseeding.
Identify the weeds in the pasture. Annual weeds are easier to control because limiting their seed production limits future weeds. Many perennials spread with underground stems along with seed production. The goal is to keep the perennials small to deplete the root stores of nutrients. This will make perennials less vigorous.
A pasture mix with lots of different perennial grasses and legume species will contribute different nutritional elements to the diet. You can affect a cow’s grazing behavior and selection of forages and forbs by making paddocks smaller. They will eat even the less desirable plants if they feel as if they are competing with their peers for the food. Clipping after grazing will help control weeds they don’t eat.
If areas are grazed down or if there are open patches in the sod, over-seed these areas in the fall. Any renovation or reseeding must use seed approved under the organic certification rules. When you reseed a pasture, it is very important to prepare a fine, firm seedbed; use a roller after cultivation and seeding. Broadcast seeds evenly over the ground. Don’t drill them in wide rows which leaves large areas open for weed establishment. Drilling seed in rows would leave 6 to 8 inches between rows. If you prefer drilling your pasture, drill lighter rates in two directions to fill open areas.
Hoe or cut weeds before they seed out, including areas not grazed.
There are some vinegar-citric acid herbicides approved for use on organic pastures. These work best when weeds are small. A propane torch can also help reduce weed growth. Flame the crown of the plant thoroughly.