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.
Below is a close-up view of spore-bearing structures.
Vegetative Stage
Shortly after emergence of spore-bearing stalks, sterile vegetative stalks
emerge and persist throughout the growing season (until frost).
In the image below, vegetative stalks have emerged as sporophytic stalks
begin to senesce.
Leaves are stiff and conifer-like, and radiate out from the central stalk.
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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Altland
