Horsetail - Equisetum arvense

Horsetail (Equisetum arvense) is a primitive spore-bearing plant in the family Equisetaceae.  It is native to the Pacific Northwest, however, it is also one of the most difficult-to-control weeds in nursery crops.

Horsetail spreads by spores or creeping rhizomes and tubers.  Rhizomes can grow to a depth of 6 feet, making control difficult even with herbicides.  Rhizomes and tubers are spread with cultivating equipment, and through this mechanism they can infest nurseries quickly.


Sporophytic stage

Spore-bearing stalks have no foliage, and emerge early in the year before vegetative stalks.

sporocarp Equisetum

Below is a close-up view of spore-bearing structures.

horsetail Equisetum


Vegetative Stage

Shortly after emergence of spore-bearing stalks, sterile vegetative stalks emerge and persist throughout the growing season (until frost).  

horsetail Equisetum

In the image below, vegetative stalks have emerged as sporophytic stalks begin to senesce.

horsetail Equisetum

Leaves are stiff and conifer-like, and radiate out from the central stalk.

horsetail Equisetum

When mature, plants can reach a height of 3 feet tall, but are usually much smaller.  Foliage occurs in whorls around the stem.  




Control

Casoron provides preemergence control.  According to the PNW Handbook, Casoron applied in three consecutive years at rates of 4, 3, and 2 lb ai/acre suppressed horsetail.  For postemergence control, consecutive applications of MCPA have proven effective.  Approximately 20 to 30% of horsetail populations are reduced with each application. However, skipping an application will allow plants to regenerate their depleted root system, and control up to this point will have been lost.  Horsetail thrives in moist soils.  Improved drainage, clean cultivation, and growing crops with dense canopies (very difficult in nursery production) are reported to slowly deplete horsetail populations.  We are currently conducting research with a local nursery to evaluate tillage and herbicide combinations for controlling horsetail in fallow rotation.

When small patches of this weed emerge in nursery fields, avoid plowing or disking through them.  Cultivation will only spread it throughout the field.  Try to isolate small patches and either dig the plants and roots out (a big job!) or spot spray with herbicides mentioned above.



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