Weed of the Week: Horesetail

Most farmers in the brown soil zone haven’t had the pleasure of meeting horsetail.

The darker the soil and the further north farmers are located, the greater the likelihood that they have had to deal with this challenging pest.

Known formally as equisetum arvense, horsetail is not your average weed. It is an ancient plant that has survived in moist soil for millennia.

The perennial can rapidly take over an area of field, spreading via spore and root rather than seed. The rhizome root system is capable of supporting the plant under all but the most intense herbicide programs.

Tillage, unless sustained over a season, is an excellent way to transplant the weed to new parts of a field as the small tubers that form as part of the rhizome are shunted about the countryside.

Most control methods are disruptive to the soil or to the other plants in the area but are necessary to prevent horsetail’s spread.

Round, jointed stems are tipped with light brown cones and grow up to 30 centimetres high. Stems die back once the spores have been released, giving way to four-sided, green stems.

While it looks like it might have leaves, the plant has only this whorl of branches that can grow up to 80 cm high.

The weed has a poisonous side and can irritate younger livestock. The dry stems can be detrimental to bale production.

The dark, felt-like rhizomes can extend up to two metres into and through the soil.

The Prairie Weed Survey of the early 2000s looked at weed populations beginning in the 1970s and ranked field horsetail between 14th and 18th most abundant.

Its presence failed to change substantively over the next 30 years.

In the 1970s it followed the soil zone map, with the exceptions of the Regina Plains and the Swift Current and Medicine Hat areas, where it had a roothold. The rest of the brown soil zone was mostly free of the pest.

By the early 2000s it wasn’t found in that region, with the exception of the border area with Montana and North Dakota in southern Saskatchewan. However, in the Peace River district it grew from being identified in 20 to 50 percent of fields to more than 50 percent.

Intense cropping or forage rotations can suppress horsetail and keep it from becoming a significant issue. However, it can quickly establish in wet, unseeded or flood damaged parts of a field.

Agronomists across the brown soil zone are now reporting instances of the pest showing up the past couple of seasons, which may be the result of sustained higher moisture levels across the Prairies.

Mowing can reduce spore production but won’t eliminate it entirely.

Amitrol can be applied to patches, but this will also eliminate the crop around the plants.

MCPA ammine can be used to control top growth in pastures, flax and cereals.

Drought is the best control, and good crops and drainage can also keep populations in check.

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