Answer: Flatweed, or false dandelion, can infest pastures that have been disturbed or have been overgrazed. Control is possible but takes a comprehensive, multifaceted approach including grazing management and possibly a low-toxicity herbicide. Creating a favorable environment for forage growth is important to prevent re-infestation.
I recommend a few options that can be combined for a holistic approach. First, if it's feasible, you can dig out the crowns if the infestation is sporadic, or use of low-toxicity herbicide as a spot treatment early in season (vinegar and citrus oil). Organic herbicides are less effective when the plant matures. For serious infestations, cultivation, cover cropping, and then replanting with perennial pasture will likely be in order, and may take two years of cultural management if pastures are heavily infested.
If cultivation is warranted, you could go in this spring with a disc, and turn the soil lightly to uproot the crowns. Be advised that false dandelion can still regrow from broken crowns, but you can help reduce the stand if you come in with an oat cover crop for the summer. You can graze the oats, and disc again in the fall and plant a diverse cover crop of something like annual rye, red clover, or crimson clover. Annual ryegrass also works well. The point of the cover cropping is to: (1) provide high plant competition to reduce the likelihood of false dandelion re-emergence; and (2) provide lots of soil carbon to feed soil microorganisms and add organic matter for building a healthy, resilient, fertile soil for the forages. Then, the following spring you could harvest the cover crop by mowing or grazing, and disc again if the weeds are still present. At this point, depending on the extent of the infestation, you could plant an annual once again, or plant a perennial pasture mix of grasses and legumes.
Then, in order to keep the pasture stand healthy, you could develop a rotational grazing plan to control the time the horses are on the pasture, as well as the recovery time needed for the pasture plants to re-grow after grazing. Basically, a short grazing period of less than four days is best, with a recovery period from 25 to 60 days (depending on the season and soil moisture: less in the spring and fall and more in the summer). Four days is good for a grazing period because after this time plants begin to regrow, and horses find it hard to resist the fresh vegetation that has not fully recovered from grazing. When the horses are re-grazing plants that are trying to grow back and recovery is not complete, overgrazing occurs and the forage plants cannot compete with the weeds.
I recommend splitting the pasture into several paddocks, as many as you can, with electric wire or poly tape. If you have nine paddocks and keep the animals on each paddock for four days, this allows about 30 days of rest for each of the other paddocks before they are grazed again. This is a good way to control grazing and ensure the forage plants have the recovery they need.
For further study, the Livestock and Pasture section of the ATTRA website offers a host of related resources, including publications, tutorials, videos, calculators, and more.
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