Horsetail, belonging to the Equisetaceae family, is a perennial plant growing 1-1/2 to 2 feet high. This plant thrives in poorly drained areas in pastures and orchards. Horsetail spreads through spores and through a creeping underground system of rhizomes. It can be toxic to some animals, so you'll want to remove it where domestic animals live. In order to kill this plant you must try a number of methods to deplete its resources.
Till the entire area with a rototiller before spore production in May. This will eliminate the plant's top growth, which provides resources to its root system underneath the soil.
Place a 2- to 3-inch layer of compost on the soil and dig it into the top 4 or 5 inches of soil. Take a soil sample to your local extension office to find out which nutrients the area lacks. Apply fertiliser, lime and other elements as recommended.
Reseed the area with a strong perennial grass. Care for the lawn meticulously, watering when it needs water and fertilising as recommended. Horsetail does not respond to nitrogen, so fertilising will help overpower the horsetail.
Care for the lawn as recommended each subsequent year. The strong grass will eventually deplete the horsetail's resources.
Cut the tops off any remaining horsetail plants that resurface before spore production in May. This will prevent further spread and eventually kill the horsetail completely.
Herbicides will not kill this plant effectively. They may also negatively affect other plants in the area around the horsetail.