Horsetail weeds, or Equisetum arvense L., show up in garden centres as bottle brush, mare weed or horse pipe. It grows in tall, vertical spikes that are covered in thin, green, horizontal spikes. Horsetail thrives in damp to soggy soil where most other plants die, making it invasive. Control horsetail weeds with an herbicide, since digging and ploughing typically do not kill the root system.
Look at the area and identify any young horsetail weeds, which look like green tubes with a pinecone-like projection at the top. Pull these up by hand so that they do not open and release their seeds.
Cut the tops off the horsetail weeds using a string trimmer. Do not cut them all the way to the ground; simply remove 1 inch or so of the plant top. This exposes the inner stem, which causes the weeds to absorb more herbicide.
Fill a garden sprayer with a brush control herbicide containing the ingredient Ammonium Sulphamate or glyphosate. Read the instructions and add water to dilute the chemical if needed.
Close the garden sprayer and spray the mixture onto all visible horsetail weeds until they are saturated.
Wait 30 days and re-examine the area for horsetail weeds that did not die or new ones that have sprouted. Re-apply the herbicide to these green weeds. Ammonium Sulphamate will typically kill horsetail weed in two applications, while glyphosate can take up to five applications.
For an organic control option, cut all horsetail weeds as close to the ground as possible and cover the soil with black trash bags. Place bricks on top of the bags to hold them down. Check the area once per month until no weeds are visible under the bags.
The herbicides will also kill all surrounding vegetation so try not to spray it on desirable plants.