Nothing sends fear into the heart of a horse owner like seeing Tansy out in the field! Tansy has been rumored to kill horses, so the sight of just one plant will send many horse owners into a tizzy! As an herbalist, I felt it was time to take a step back and look at Tansy as any other herb. Some are good, some are good only in small doses, and some should be respected and avoided.
I’ve heard the argument in our area about whether we have Tansy growing in our fields or whether we have ragwort growing in our fields…well, actually it's both. Tansy IS a ragwort and is actually called “Tansy Ragwort”.
Tansy Ragwort (Senecio Jacobaea) is an invasive toxic weed that was introduced to the United States from Europe. It is most often found in pastures and fields. Most animals avoid eating Tansy because of its bitter taste, but if enough is ingested (the estimated amount for a horse is 35lbs, but this is subjective) it can cause liver damage and lead to death. The highest risk of ingestion is after the plants have been mixed in with hay because the plants are not as bitter tasting but just as toxic.
Tansy Ragwort is often confused with Common Tansy (Tanacetum vulgare). Common Tansy is considered less toxic and is also not generally consumed by livestock because of its naturally strong odor and very bitter taste. The two "Tansies" are best distinguished by their flowers. Tansy Ragwort has outer petals on its blooms and Common Tansy has button-like blooms with no outer petals.
In either case, whether you have Tansy Ragwort or Common Tansy, you have a quickly spreading noxious plant on your hands, but is it something to panic over? No. The reason Tansy is a health issue is because of the high alkaloids called pyrrolizidine.
This is the plant’s natural defense that causes it to be very bitter so that plant-eating insects and animals will avoid it. When someone states that Tansy killed their horse, it's not because it took one bite and killed over dead on the spot! It had to ingest that Tansy for weeks or possibly months in order for the alkaloids to poison the liver and cause liver failure, or have a pre-existing condition that made it susceptible to the Tansy's alkaloids. Because of its bitter taste, a horse will only eat Tansy when there is not enough food provided otherwise.
From an herbalists point of view, Tansy as an herb (when taken properly) actually has some health benefits.
Tansy has been used for digestive issues including stomach and intestinal ulcers, gas, bloating, stomachaches, and poor appetite. It has also shown positive uses for migraines, nerve and joint pain and sciatica. It's been used for heart conditions including rapid palpitations and fluid retention caused by congestive heart failure. Tansy has been successfully used to treat roundworm and threadworm infections in children. Tansy also has topical uses as well and has been used as a wash for scabies, itching, bruises, sores, sprains, swelling, inflammation, and tumors. It is also applied to the skin as an insect repellent.
Be careful not to confuse Common Tansy (Tanacetum Species) with Tansy Ragwort (Senecio species) and other plants generically referred to as “Tansy.” Even though they are related, as an herb they are not considered to have the same benefits.
How does it work?
The chemicals in Tansy increase saliva and blood flow to the tissues in the mouth, stomach, and intestines. Tansy extracts may decrease pain, increase bile production, and increase appetite in people with liver and gallbladder problems.
Now, this does not in any way make Tansy “safe”. As a type of Ragwort, it also comes with a list of side effects, especially to those with Ragwort allergies. This is just to say that Tansy, as an herb, does have its uses in the world.
So why get the tansy out of your fields?
First and foremost is “risk”. As Tansy does have its downsides, it is best to not risk keeping it around. Second, as a noxious week, it is going to spread quickly and take up valuable grazing land! This in itself is a reason to give it the boot! And lastly, let's be honest, it's an ugly weed! Does anything look worse than a field full of tansy? In many areas, it has been tagged a “noxious” invasive weed and its removal is required by many counties. So, give it the boot early before it becomes very difficult to get rid of!
Though Tansy is nothing to panic over, it is certainly not worth the risk to keep it around.
(photo by Nikk on FLICKR-"Lycaena phlaeas - Small Copper")