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"Poisonous" does not mean deadly. Some manifestations of toxicity are subtle. The dose, as always, determines if a plant is safe source of nutrients or a toxic hazard.

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BRIEF: How can I get rid of this horsetail (equisetum arvense)?

I am wondering how to successfully rid my property of horsetail. A neighbor of ours has a relative who works for Ortho Chemical and he did not know of a chemical solution (to kill this plant)...which is not a good option for us anyway as there is a pond with fish and wild birds (herons, wood ducks, red-winged blackbirds) at one end of our property where this weed is prevalent. If we plow the fields under repeatedly where it is growing, will that short-circuit its growing cycle? I know it likes 'poor soil'.


Horses can often avoid horsetails well enough if there is plenty of other feed and, therefore, they are not often poisoned by this plant in a grazing situation. They are slightly more likely to eat ferns in a pasture, but even there, poisoning in the presence of other good pasture is not too common. Pteridophyte (ferns and horsetails) poisoning becomes a problem if there is nothing else to eat, or (most common cause in the US) if pteridophytes are cut and baled into hay. Hays containing 20% horsetail or bracken fern will result in thiamin-deficiency symptoms in 2-5 weeks. So, if you just have a few horsetails in one end of a good pasture that you never cut for hay or overgraze, you may get away with this. If you plan to cut it for hay or force the horses to eat the pasture down low, then you might want to get rid of the horsetails, or fence the horses out of that area and turn this wet ground over to the birds and wildlife. I am not an expert in weed control, but I think that if you want to get rid of horsetails, then plowing (to get rid of underground plant structures) and a good subterranean tile drainage system would help pasture plants out-compete the horsetail. On drier ground, after a good plowing and a seeding with competitive pasture plants, the horsetails will not be as plentiful, if they can grow at all.