Field horsetail, Common horsetail, Bottlebrush, Foxtail, Mare’s tail, Horse pipes, Snake grass, Scouring rush (figures 1, 2, and 3 below), Scourweed, Pinetop.
Description
Characteristics
Horsetail, (Equisetum arvense L.), belongs to a prehistoric plant family that was dominant in the world 230 million years ago and significantly contributed to the formation of coal deposits. The Equisetum family contains over 30 plant species and is native nearly worldwide, excepting Australia, New Zealand, and Antarctica. The Pacific Northwest is home to about 20 Equisetum species.

All horsetail species are considered toxic to livestock (particularly horses), but are low in palatability and rarely eaten unless fed with hay. Field horsetail thrives in acidic, poorly drained sandy or gravelly soils and full sun. Although it is considered a wetland plant, it can also be found in drier areas.
Control Methods
Cultural Control
Control of horsetail and scouring rush is similar, so this document will focus on horsetail management. Because horsetail does not respond to nitrogen fertilization and wants sunlight, its growth can be suppressed through the use of a fertility program and competitive cover crops. Other control options that have met with some success include use of inorganic mulches and weed barrier fabrics. Improving drainage in the area can also be helpful.

Scout a field for beginning establishment or infestations of horsetail or scouring rush. The tenacious root system of field horsetail and scouring rush makes it very difficult to control, particularly when using mechanical methods that can actually worsen the problem by spreading rhizomatous pieces that can regenerate. The fertile horsetail stems should be cut or burned before they form spores in order to reduce spread potential. Repetitive tillage or mowing over at least a 2-year period may be effective if timed to eliminate regrowth before the plants are able to replenish their energy reserves—shortly after emergence and before reaching 8 inches in height. Shallow tillage is not recommended. It has been determined that six years after introduction into an agriculture field, horsetail will infest 2.5 acres (Cloutier and Watson, 1985). This can be much higher or lower depending on management techniques. Horsetail negatively reacts to shady conditions and may be limited within a vigorous competitive crop. As mentioned before, the application of lime and fertilization can positively influence crop competition and negatively impact horsetail spread. As is the case with most invasive plants, the most effective management approach will involve a combination of methods, such as applying herbicides after mowing.
Few herbicides have any effect on field horsetail and their use depends on the situation in which it grows. In non-crop areas, diclobenil (Casaron®) and chlorsulfuron (Telar® and Oust®) are labeled for field horsetail use. Various MCPA formulations will provide top growth control in grass pastures and cereals. Multiple chemical treatments may be necessary.
More information can be found in the PNW Weed Management Handbook.
Biological Control
No biological control agents are available.
Scouringrush examples:


