Ragwort is an invasive weed native to Europe and Western Asia.
But now, it is found throughout the West, Midwest, and Northwest parts of the United States.
The rosettes of ragwort are the most toxic part of the plant and have caused the death of livestock such as cattle and horses.
Sheep are one of the only animals seemingly unaffected by the toxins in ragwort.
So, is it possible for sheep to kill ragwort?
If sheep are allowed to graze in areas where ragwort grows, they may be able to eliminate the invasive weed over time. However, too much of the weed is toxic. Ragwort is difficult to kill because it spreads very quickly. It would likely take several years of grazing before the sheep could entirely eliminate it.
Sheep will only eat the top part of the ragwort, so the bottom of the plant may survive.
If the sheep can graze on the ragwort before it produces seeds, the plant will not be able to propagate.
Read on to learn the symptoms of ragwort poisoning and why sheep are not affected by the toxins.
Why Are Sheep Not Sensitive to Ragwort Poisoning?
Sheep can tolerate the toxic pyrrolizidine alkaloids found in common ragwort.
But they are not completely immune to its effects.
Only adult sheep are seemingly unaffected by ragwort poisoning.
Young sheep who ingest ragwort may show mild symptoms, and studies have been conducted on lambs consuming the plant.
The studies show lambs who regularly ate ragwort had a slower growth rate than those who had not ingested ragwort.
It is not yet if there are any long-term residual effects on lambs who have eaten ragwort.
As a precaution, avoiding allowing lambs or pregnant ewes to graze in pastures with ragwort growth is recommended.
Other Methods of Controlling Ragwort
Tansy ragwort flowers form seeds in July and August from late spring to late summer.
The ragwort plant thrives in areas with cooler temperatures and heavy rainfall.
Overgrazed agricultural fields and land recently devastated by wildfires are the most common places to find ragwort.
Ragwort is a biennial weed and does not flower until its second year when it spreads seeds and dies.
There is some controversy over the control of tansy ragwort, as conservationists say the pernicious weed is necessary for pollinating insects to thrive.
For this reason, ragwort elimination is limited to pasture management in agricultural fields where livestock may graze.
The control of tansy ragwort must be done carefully to completely stop the spread of this invasive, poisonous weed.
There are several methods for controlling tansy ragwort species, some of which have proven more successful than others.
Proper agricultural management practices are necessary to prevent ragwort from growing where livestock grazes.
Continuous grazing will destroy the plant life in a pasture and leave bare spots where common ragwort can thrive.
Rotational grazing, where livestock is regularly moved to graze in different areas, prevents the pasture from being overgrazed.
Maintaining a dense pasture makes it more difficult for common ragwort seeds to become established.
Cutting is the least effective method in the control of tansy ragwort, and it is not recommended.
If tansy ragwort flowers are cut after producing seeds, it will encourage the pernicious weed to come back vigorously the following year.
To avoid seed germination, you must take special care to ensure the ragwort cuttings are removed.
Any part of the ragwort plant left in the ground will quickly grow back within a few weeks.
Cutting tansy ragwort flowers only seems to exacerbate the weed problem.
The only way to get results from this method is by frequent cutting and proper grassland management.
Eliminating field mice, gophers, and moles from grasslands prevents these rodents from destroying healthy grass.
Even with routine cutting and grassland management practices, it could take years to see any results of ragwort control.
Pulling out common ragwort is only effective if done correctly.
Removing ragwort plants in the spring or winter without leaving any roots behind is challenging.
Another issue with pulling ragwort is the proper disposal of the flowering seed heads.
The seed heads of ragwort must be carefully bagged to avoid spreading the seeds.
Burning or composting the seed heads has to be done to prevent the common ragwort seeds from germinating.
Various herbicides have been used to control tansy ragwort with mixed results.
Applying enough herbicides to kill ragwort effectively is difficult, and several applications are necessary.
Herbicides must also be applied while the ragwort is actively growing to work.
Fall and spring herbicide applications are best.
Repeated herbicide use is also harmful to the environment, so this is not a favorable method of ragwort removal.
Using Biocontrol Agents
Several insect species have been introduced to control ragwort.
In Oregon, the cinnabar moth, adult ragwort flea beetles, and the seed head fly were introduced from 1960-1971.
The larva from these insects feed on the common ragwort plant, and they were imported from Western Europe, where the poisonous weed originated.
Once the insects became established in Oregon, they were collected and released in affected areas throughout the state.
The insects were very effective as biocontrol agents, and there was a decline in ragwort infestations by the 1980s.
Adult flea beetles had the most significant impact by feeding on the ragwort rosettes in the winter, causing the smaller rosettes to die.
The flea beetle larvae eat the root crown and leaf stalks.
Unfortunately, infestations of tansy ragwort increased in 2005 due to a winter drought followed by a wet spring.
More recently, the ragwort plume moth was released in Australia in 1999 and New Zealand in 2006 to control marsh ragwort.
In the late spring, adult moths deposit egg clusters on the underside of leaves so the larvae will feed on them.
Since the ragwort plume moth was released in these areas, marsh ragwort infestations have declined by 60%-80%.
Marsh ragwort is still common in parts of Europe, where insects have not been released.
Symptoms of Ragwort Poisoning in Other Livestock
Common ragwort plants produce toxins called pyrrolizidine alkaloids, which are poisonous to humans and most livestock when ingested.
Cows and horses generally do not prefer to eat ragwort, but if the pasture is bare due to continuous grazing, it may be the only plant available.
When cows suffer from mineral deficiencies, they are more likely to seek out ragwort in the pasture.
If hay is cut from a field containing ragwort, it becomes contaminated.
Contaminated hay will easily kill an entire herd of cattle if the farmer does not know it contains ragwort.
The pyrrolizidine alkaloids in common ragwort plants cause liver cirrhosis, which is the cause of death in livestock.
If large amounts of ragwort are consumed, the poisoning will be acute, and the animal will die within a few days.
The toxic effects of ragwort are usually chronic and cumulative, meaning the poisons build up in the animal’s liver over time.
An animal may appear to be healthy for weeks and months after eating ragwort before there are noticeable symptoms followed by death.
No antidote or palliative treatment is available for animals suffering from severe ragwort poisoning.
Symptoms in Cows
Symptoms of ragwort toxicity in cows include:
- Loss of appetite
- Severe diarrhea
- Swollen abdomen
Often, if a cow is straining with diarrhea, it will suffer from a prolapsed rectum.
The affected cow may become aggressive and unapproachable before it eventually dies.
Symptoms in Horses
The symptoms of ragwort poisoning in horses are similar to the signs in cows and include:
- Loss of appetite
- Weight loss
- Skin sensitivity to sunlight
- Compulsive walking
Symptoms of ragwort poisoning in horses may not become apparent until anywhere from 4 weeks to 6 months after plant ingestion.
Once the symptoms appear, the liver has already failed, and death is imminent.
In severe cases where the horse displays abnormal behavior, the animal may die in as little as ten days.
Symptoms of Ragwort Poisoning in Chickens
Tansy ragwort poisoning in chickens produces symptoms such as:
- Loss of appetite
- Behavioral abnormalities
- Excessive drinking
Chickens suffering from liver disease may only have vague symptoms, often confused with other illnesses.
Ragwort poisoning will occur in all breeds, and ages of chickens, but not every bird in the flock will show signs of liver damage.
Symptoms of Ragwort Poisoning in Pigs
The symptoms of ragwort poisoning in pigs are not as noticeable but include:
- Loss of appetite
- Rapid breathing
- Weight loss
The effects of ragwort poisoning in pigs are typically cumulative, and it takes a couple of months for the animal to show symptoms before dying.