Ferns are airy, delightful plants that are generally considered harmless and add a cool greenery to the landscape. Bracken ferns are a nuisance plant that grows and reproduces vigorously once it has been introduced. The plant grows naturally in the woods but is classified as a weed on farmland. It has toxic effects on livestock that graze on it and is allelopathic to other plants. It produces chemicals that can kill off competing species. Bracken fern grows via rhizomes and is extremely hard to remove mechanically. The presence of the fern in pastureland is potentially dangerous, and control of the plant is a necessary part of maintenance.
Mow the pasture on the highest height setting in summer. Summer is the most effective time to apply the herbicide, and it works best after cutting the ferns. The ferns have little stored energy in the rhizomes at this time and recovery from the herbicide will be difficult if not impossible.
Rake up the fern heads after mowing to prevent the spread of the plant. Bracken ferns reproduce from spores contained in the heads. They can also reproduce vegetatively through the rhizomes.
Measure the recommended amount of Asulam into the sprayer and add water as directions indicate. Asulam is effective against bracken fern and is a selective herbicide that is environmentally safe.
Walk the pasture and spot-spray the fern locations. Dead foliage should be cut away from trees after being treated with the Asulam. It will take a few days to be sure the plants are dying.
Cover the infested areas with black tarp and hold it down with rocks. Bracken fern needs light to survive, and this will cut out light to any plants that are resprouting. It will also heat up the soil and kill some of the rhizomes.
Spray again at the end of the summer or early fall to ensure control. The herbicide works best with a second application. The pasture should be free of bracken in the spring.