Ask the Expert -- Poisonous Plants

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What is alsike clover, and is it toxic to horses?
Which plants should I avoid planting near a bioretention basin?
We found some dried Bull's Nettle in our hay. Should we be concerned?
How do I get rid of buttercups?
Which cherry tree species are toxic? How long do their leaves stay toxic?
Are chestnuts poisonous to horses?
Is Hemlock poisonous to horses?
Are holly trees poisonous to horses?
How do I get rid of Horse Nettle?
Is there a test for Horse Nettle poisoning?
Is it okay to plant Juniper near my riding arena?
Are mulberries toxic to horses?
Are oak leaves, acorns, and bark toxic to horses?
What are some plants I can plant around my paddocks?
Are Red Maple leaves poisonous to horses?
Are tomatoes poisonous to donkeys and horses?
How can I make sure there are no toxic plants on my farm?
Which trees are toxic to horses?
Is Star of Bethlehem toxic? How do I get rid of it?
Is Wax Leaf Ligustrum poisonous to horses?
Are Wisteria plants poisonous to horses?

Both of my horses are being treated for presumed alsike clover toxicity – a danger which many horse owners are unaware of. From my experience, alsike clover is extremely common in northern NJ pastures. I think this year's weather patterns have made it more toxic than usual at this time of year. It is usually more of an issue in April (lush growth) and September (stressed plants). It would be extremely helpful if you could help raise awareness of this extremely critical problem.

The goal of this reply is to educate the horse public on the potential problem with horses consuming alsike clover:

Alsike clover (Trifolium hybridum) is found most frequently in Canada, but has been included in some commonly used pasture mixes in the US. This plant is adapted to cool climates and heavy, poorly drained clay soils.

It grows 15-30 inches tall, and has a small ½-inch diameter pink flower that forms at the ends of secondary branches from the main stem. It should be differentiated from red clover, which has a larger flower, hairy stems and leaves and a white inverted "V" on the leaf. Alsike clover is known to cause two syndromes, photosensitization (short-term exposure) and "big liver syndrome" (long-term exposure). There is also a potential for nitrate poisoning. The more common and acute lesions related to photosensitization are characterized by:

Possible symptoms of nervous and digestive disorders, including colic and diarrhea and oral lesions related to alsike clover poisoning may also be observed.

The long-term consequence of alsike clover consumption is "big liver syndrome," appearing as a progressive destruction of the liver with increased connective tissue (appears as an enlarged liver). It appears that this is related to the accumulation of a still-unknown toxin. The primary tests for evaluating liver function and hepatic disease measure the serum enzyme activity of aspartate amino transferase (AST), gamma glutamyl transferase (GGT), sorbitol dehydrogenase (SDH) and lactic dehydrogenase - 5 (LDH-5). Liver biopsy may be required to characterize the degree and type of liver damage and provide a prognosis.

Alsike clover poisoning does not appear to occur every time it is consumed. It is thought that the toxicity may be caused by a mycotoxin which is either created by a fungus growing on the plant, or created/accumulated by the plant under stressful growing conditions. However, horse owners should still take the following precautions:

Answer provided by Carey Williams, Ph.D., Rutgers Cooperative Research and Extension.

We have several native plants that we are planning on using for a bioretention basin on the farm. Could you please let me know if any of these are poisonous to horses?

Nothing on the list is on the major "hit list” of toxic plants - but the following plants on your list have the potential to be toxic to livestock:

None of the other plants have been reported to be toxic. The aster family contains very safe plants. Dogwoods and willows are safe shrubs.

Horses are very good at avoiding toxic plants if they are healthy and have adequate forage available. The toxins in poisonous plants generally have a bitter, acrid taste and odor, which helps the horses avoid the plants. Having said that, I think it would be good to avoid planting anything toxic in or near the bioretention basins especially since this could aid in the spread of toxic plants downstream.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

We recently discovered pieces of what we have identified as bull nettle (Solanum carolinese) in our hay supply. The samples we found are dried out and have berries. We would like to know how dangerous this is to our herd. How much do they have to ingest in order for it to be dangerous and what are the symptoms we should look for?

Solanum carolinese (Bull or Horse Nettle), also known as a form of nightshade, carries a very toxic substance composed of glycoalkaloids. Due to its composition, horse nettle’s glycoalkaloids can cause GI irritation, since they are so poorly absorbed by the GI tract. Even though the plant does lose some of its toxic characteristics when dried out, the toxins are still present within the plant. Therefore, the plant poses a very dangerous stance to horses ingesting them within their food source. Horses usually steer clear of this dangerous plant, but if the hay source has been highly processed, it becomes more difficult for the horse to sort out the plant from the hay source itself. Also, since the given situation mentions that the berries are still present on the plant sample found, that fact alone makes the plant seem even more toxic, and therefore more dangerous for the horse. Researchers say, “green berries are more toxic than red or black berries, which are more toxic than leaves, which are more toxic than stems or roots” (http://www.aun.edu.eg/distance/pharmacy/poison/black_nightshade.htm). Therefore, the toxicity can range from high to semi-low depending on the ripeness of the berries on the plant. The toxicity of a given species can vary widely due to environmental conditions, part of the plant or degree of maturity. Some reports conclude that one to ten pounds of ingested plant material were deadly for horses.

Some symptoms one should be on the look out for are dilation of pupils, diarrhea, loss of appetite, and loss of muscular coordination. The plant basically affects the central nervous system and the GI tract, because of its glycoalkaloidic composition. Some other signs that may warn you that your horse has been potentially poisoned by Horse Nettle are if the horse enters a sudden state of depression, appears to be affected by apparent hallucinations, and if the horse goes into convulsions. If the animal had been consistently ingesting the contaminated hay, their apparent symptoms of ingestion would be depression, diarrhea, and/or constipation. In order to keep your horse safe, check your hay supply frequently for potentially dangerous plants. Horses naturally avoid these plants when grazing, so it should not have to be removed from grazing areas.

Answer prepared by Stephanie Cruz, Animal Science Research Student at the School of Environmental and Biological Sciences, Rutgers University.

Buttercups seem to be taking over my pasture this year. How do I get rid of them?

Pasture composition constantly fluctuates in response to changes in environmental conditions. 2005 appears to be the "year of the buttercup" judging by the concentration of buttercups in local pastures and the number of requests for information about the plant that we have received.

There are many species of buttercups found in New Jersey. Some species prefer wet conditions, other survive in dry pastures. Buttercups are perennial plants that over-winter as corms and reproduce by seed. They are very common in the state and are found in virtually all pasture situations. They thrive in low fertility soils and in overgrazed pastures.

Buttercups can be toxic to livestock, but are extremely unpalatable. Animals that are healthy, well-fed, and have access to plenty of pasture or hay rarely consume buttercups or other toxic plants. The fresh leaves and flowers of all buttercup species are toxic when consumed fresh, but the plants lose their toxic properties when dried in hay. If the plant is consumed, horses will exhibit signs of severe gastritis, marked by increased salivation, decreased appetite, colic and diarrhea. In severe cases, poisoning may lead to convulsions and death.

The best defense against buttercups, and all weeds for that matter, is to maintain a healthy stand of forage grasses. Cool season grasses such as bluegrass, perennial rye, orchardgrass, brome and timothy grow rapidly in spring. Fertilizing grasses and rotating pastures to encourage the grasses to remain thick and healthy allows them to out-compete weeds by preventing bare spots and shading the ground. Thick pasture grasses allow little room for the establishment of weed seedlings. Frequent mowing will also reduce buttercup seed production.

Since buttercups are perennials, once they are heavily established in a pasture, it may be necessary to use an herbicide to remove them. It may take several herbicide applications to reduce the population of buttercups. You may want to contact a local crop production service representative or hire a commercial applicator to apply herbicides. Turf type "weed and feed" products are not labeled for use on pastures.

Fortunately, Ally/Cimarron is a very safe and effective herbicide for controlling buttercups. Ally is a liquid, soil-applied herbicide that moves into the plant through the root system. Ally can be applied in spring or early summer at the rate of .1 to .3 oz per acre. There is no grazing restriction for Ally and horses can be returned to the pastures immediately. It is also possible to tank-mix Ally with liquid fertilizers in spring. Ally should only be applied to grasses that have been established for at least 6 months. For timothy, at least 12 months is desirable and tall fescue should be established for at least 24 months. Ally is very persistent in the soil, therefore crop rotation guidelines must be adhered to. Ally should not be used if you plan to overseed the pastures, since the herbicide will remove new grass seedlings as well as the weeds.

A combination of 2,4-D and Banvel can also be used to reduce buttercup populations. These products are also applied as a liquid but translocate through the plant to the roots. The best time to kill buttercups with this herbicide combination is in spring, before flowering, or in late summer, when the plants are moving food from the leaves to the roots. Grasses should be well established before applying 2,4-D/Banvel, but pastures can generally be overseeded 4-6 weeks after an application of these products. There is a seven day grazing restriction for certain formulations of 2,4-D and different manufacturer's products may have various grazing restrictions. Always carefully read the label before using any pesticide.

Remember that Ally and 2,4-D/Banvel are broadleaf herbicides that will also eliminate existing clover plants in pastures.

For assistance in identifying and controlling weeds in pastures, contact your local Cooperative Extension Office. Use pesticides only when necessary at the correct rate and time. Read the complete label and follow all precautions listed. Where trade names appear, no discrimination is intended and no endorsement is implied.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

We have a grass area in which I would like to graze a colt, but it has two cherry trees in it. I am having the trees removed, but there are still some old leaves from last Fall in the grass, and it would be nearly impossible to remove all of them. Since these leaves are from last Fall, has enough time passed to render them harmless? There is also a lot of bark that came off the trees when we removed them; is this part toxic? If so, what are the species of cherry trees that are toxic to horses?

All species of cherry trees are toxic to horses. The seeds, leaves, and bark are the most toxic parts of the plant; fruits are the only relatively safe part. As for the leaves, usually the toxicity is worst when they are in the stressed state prior to dying or are wilted (e.g. leaves on a fallen tree limb lying in a pasture). This is the point when the leaves are not only toxic but very tasty because they have stored a lot of sugar and are sweet and palatable.

Once the leaves have fallen off the tree in the autumn they are dead and no longer palatable to horses. Dried leaves will also contain much less toxin than freshly wilted leaves. By this point, horses will typically not hunt out leaves and consume them because the remaining grasses are much more palatable to them. If a horse consumes a few leaves here and there it is not enough to be a problem. However, putting an exact amount on what they need to consume is not possible either. No research has been done on this. Clinical veterinary findings of poisoning cases usually directly involve downed tree limbs where the horses have cleared off all the leaves.

It is advisable to make sure your horses have plenty of grass, hay or other forage to deter them from eating leaves or anything else they typically would not consume. Cherry leaves contain a precursor to cyanide which binds and interferes with the cellular use of oxygen. If an animal does consume a large enough amount of this toxin, it will basically suffocate. Early signs of poisoning are hard to catch since they come on very rapidly. Death is usually the first sign that something is wrong. If anything is suspected a veterinarian should be called immediately. An antidote can be administered, but it needs to be done as soon as possible.

Answer provided by Carey Williams, Ph.D., Equine Extension Specialist, Rutgers Cooperative Extension.

Yes, Horse Chestnuts or Buckeyes (trees) are toxic to horses. The toxicity level is moderate to high. The poisonous parts include leaves, seeds, young sprouts; poisoning is more common in spring due to early sprouting. The symptoms of toxicity include gastrointestinal irritation and neurological signs.

What kinds of Hemlock are poisonous to horses? What are the symptoms of Hemlock poisoning, and how can it be treated?

Poison hemlock (Conium maculatum) and water hemlock (Cicuta species) grow abundantly throughout the United States. They prefer moist areas and will reproduce prolifically if left unchecked. They are especially abundant in the spring, a time when enough forage may not be available. They may also be more palatable while growing and can grow to be anywhere from two to eight feet tall. A purple-spotted hollow stem with triangular pinnate leaves is observed on the plants. Small white flowers appear in early summer, arranged on the stem in an umbrella-like fashion. The small, gray-brown seeds are egg-shaped and ridged. The leaves and stems are the most toxic part of poison hemlock before the seeds develop. These plants have a tap root with a pungent odor.

Poison hemlock and water hemlock look similar and are typically mistaken for one another. Water hemlock leaks a yellow, foul-smelling liquid when cut. The poisoning symptoms of the two plants are also similar, but treatment for each tends to be different. Therefore, in cases of suspected poisoning, it is important to properly identify the plant.

Hemlock poisoning presents many symptoms, including nervousness, salivation, frequent urination and sometimes birth defects. Symptoms of poison hemlock poisoning progress in a predictable order. Within two hours after ingesting the plant, the affected animal first becomes nervous, then uncoordinated, and finally starts to tremble. Following this excitatory stage there is a depressed state in which the respiratory and heart rates fall, causing the extremities to become cold. The animal’s entire metabolism then starts to slow down, making colic or bloating possible. The animal can remain in this state for several hours or even days and then recover. Large doses of the plant may cause paralysis.

A lethal dose of poison hemlock is four to five pounds of leaves. In fatal poisoning cases, the animal will die five to ten hours after the first symptoms are seen. Death is usually caused by respiratory failure; the mucous membranes will be cyanotic (blue) due to a lack of oxygen.

The toxicity of poison hemlock lies in its alkaloid content. Alkaloids in hemlock plants block the reflexive movements of the spinal cord.

Water Hemlock. Photo courtesy of Colorado State University. Click for larger image.

With water hemlock, cicutoxin, and cicutol, potent unsaturated alcohols, are found in all parts of the plant. The roots are highly poisonous at all stages of the plant’s life cycle. Horses eating as little as 2 ounces of the root could potentially die. Milder symptoms of water hemlock poisoning include excessive salivation, teeth grinding, and eventual convulsions leading to muscle degeneration and heart failure and respiratory paralysis.

There is no treatment for hemlock poisoning, but a veterinarian should be called immediately if you suspect that an animal ingested either hemlock. The veterinarian will provide supportive care to treat the symptoms that present. In order for the horse to recover, the toxin has to be eliminated from the gastrointestinal tract.

The best way to deal with hemlock poisoning is to prevent it. This can be done by mowing down the plants or pulling them up by the roots. Hemlock is hardy, so it may be difficult to eliminate. If herbicides (like 2,4-D) are used, the animals will have to be removed from the treated area until the herbicide is washed away and the plant removed because treated plants may be more palatable.

Indiana Plants Poisonous to Livestock and Pets: http://vet.purdue.edu/depts/addl/toxic/by_alpha.htm

Guide to Poisonous Plants: http://southcampus.colostate.edu/poisonous_plants/index.cfm

Answer provided with the help of Christine Garnier, Rutgers University, Equine Research Student.

It does appear that Holly is moderately toxic to horses. Some of the symptoms would include digestive upset, or colic, more severely leading to tremors or seizures. The toxic parts of the plant include but are not limited to the berries. I would recommend not planting Holly trees where horses can gain access to them. Most horses will not eat trees if given a choice of other fresh hay or forage; however, some horses can acquire a taste for anything. Most toxic plants are unpalatable and give off a bitter taste and/or smell.

Horse nettle in a hay field (assuming we are talking about a grass hay field and not an alfalfa-grass mix ) can be controlled with the use of a commercial herbicide. It is a perennial weed, so early fall is a good time for control. Control can even be attempted in early spring when there is active plant growth. However, I would strongly advise contacting your local extension agent at your state’s Land Grant Institution to make sure that the product you select is labeled for use in your state. If not, it will not be legal for you to use. The labels must also be checked for grazing restrictions and pre-harvest intervals. Again, I recommend checking with your local extension service for control recommendations.

Answer provided by Bill Bamka, Rutgers Cooperative Extension, Burlington County Associate Professor/County Agriculture Agent, Field and Forage Crops.

I found out that my horse has been eating Horse Nettle. Over the past month he has been sweating unexplainably, tensing his abdominal and moving slower. Can any tests be done to find out if he is suffering from this toxic plant?

Horse nettle (Solanum carolinense) is a very common weed that grows in crop fields, pastures, and is frequently found in hay. Plants can easily be recognized by their deeply lobed leaves that are prickly on the underside. The stem of the plant is pubescent and also contains numerous pickers. Flowers are purple, yellow, or white and the fruit is yellow/orange in color and looks like small tomatoes. Horse nettle is in the nightshade family (a very large family that also contains ground cherry, and black and bitter nightshade). Our cultivated potatoes and tomatoes are also in this family.

Horse Nettle blossom in spring. Click for larger picture.

Virtually all horse pastures contain some toxic plants or shrubs. The toxins in the plants serve to deter browsing and have a bitter or acrid taste to prevent the horses from consuming the plant. Healthy horses that have access to adequate forage in pasture or as supplemental hay rarely consume toxic plants. The prickly surface of the leaves and stem of horse nettle further serves to discourage animals from consuming this plant. It would be important to actually see your horse eating the plant or discover significant evidence of browsing before assuming that your horse has been eating horse nettle.

If you see your horse consuming horse nettle in pasture, remove your horse from the pasture. Mowing can be used to reduce the spread of horse nettle, but since it is a perennial weed, mowing will probably not eliminate the plant. Herbicides can be used to remove the toxic plant but need to be used when the plant is actively growing. The best time to control horse nettle in the northeast is when it is flowering or in late summer.

Horse nettle contains a steroidal alkaloid called solanine that blocks the action of cholinesterase on the central nervous system. Symptoms of poisoning include decreased salivation and intestinal motility, which can lead to colic, constipation and bloody diarrhea. Animals also sometimes exhibit signs of trembling and paralysis. Some veterinary and teaching hospitals are capable of screening blood for the presence of a specific toxin, in this case solanine. This will confirm your suspicion that your horse is consuming the plant.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

We want to plant some type of slow-growing plants on a bank outside of a newly made riding arena. I'm afraid to plant something that could possibly be toxic. I would like to plant a running juniper, which would take over the bank but not be a problem to manage. I have had mulch placed there but I need a stabilizer to keep the mulch from washing down into the arena. What do you suggest?

Junipers are indicated as toxic in many plant references. Therefore, I would tend to err on the side of caution and avoid planting any juniper species near a paddock or arena.

Depending on the slope length and gradient of your bank, you might consider terracing or geotextiles in combination with grass plantings for stabilization. I suggest you contact your local USDA Natural Resources Conservation Service (NRCS) office or the local soil conservation district and seek their advice for steep slope planting. The NRCS staff has specialists that deal with erosion and sediment control.

Answer provided by Bill Bamka, Rutgers Cooperative Extension, Burlington County Associate Professor/County Agriculture Agent, Field and Forage Crops.

I am looking to find information on adverse effects, if any, that mulberries might have on horses. My 4-year-old gelding is eating those that have fallen from the trees and I am concerned.

Mulberries are not known to have toxic potential to horses. However, it is important to keep in mind that even plants considered to be non-toxic can still produce minor stomach upset if ingested - especially if they are consumed in a large quantity. They are sweet and are probably like a treat to him. If there is a way you can try to clean up the berries from the pasture or try to avoid them, that might be a good idea, however, they probably will not cause more than digestive upset.

I have mature oak trees on my property. My horses are exposed to the leaves that fall into their pens and the arena. There is one tree that is close enough to the arena that they could eat the bark if they wanted to. Are oak leaves, acorns, and bark toxic to horses?

Oak can be moderately toxic to horses. However, cattle are the species most often affected by oak toxicosis. The reason why horses aren't more affected is because of their unwillingness to consume the leaves and acorns. There are some horses that may find the taste palatable. If provided with plenty of good hay or pasture, most horses will not choose to consume the oak detritus. So if you are turning your horses out into an arena where there is only sand and some oak leaves and acorns, I would consider throwing them some hay to consume instead of giving them the option of the oak parts.

Answer provided by Carey Williams, Ph.D., Rutgers Cooperative Research and Extension.

Do you have any suggestions as to what types of trees or plants horses will not eat? I want to plant a privacy screen around the outside of a fence surrounding my horses’ paddocks.

Although we consider horses to be grazing animals, there is growing evidence that indicates that horses may have evolved to be browsers. They are grazers because we confine them to pastures that are planted in grasses and they do not have access to anything else. Left on their own, horses would primarily eat grasses, but would also browse on herbaceous weeds, trees, vines, and shrubs. Therefore a general rule of thumb is that if a plant is not toxic and horses have access to it, there is a high probability that they will browse on it. Trees, shrubs, and ornamental plantings should be planted outside of the pastures and set back far enough that future plant growth will not provide horses with opportunities to consume or nibble on the plants.

Bright colors are often associated with toxic plants and serve to warn animals about a plant’s toxic status. Many brightly colored ornamentals, such as foxglove, wisteria, lilies, daffodils, rhododendron, etc. are highly toxic to animals. Therefore it is not a good idea to plant ornamental plants within reach of livestock.

If you wish to plant trees to supply shade, plant the trees outside of the pasture and set them back far enough that the animals cannot browse on them as they grow. Horse will strip bark off of the trees if they are placed in the pasture and may girdle the tree and kill it. If you must plant the trees in the pasture, construct a fence around the trees to prevent access to them.

Native red maples (and ornamental red maple cultivars) are highly toxic to horses. Although sugar, silver and Norway maples contain some of the toxin that is found in red maple, the concentration is so low that they are not considered to be toxic to horses. Maples grow fairly rapidly and are attractive shade trees.

Many other trees are acceptable as perimeter plantings. Other trees to avoid due to their toxic properties include black locust, horse chestnut, oaks, and cherry.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

I know that Red Maple leaves are poisonous to horses, however, how much does it take to cause a problem? I have seen leaves in my pasture that resemble Red Maple, and asked my vet who told me they weren't. However, I looked up a photo of the leaves and that is exactly what I have in my pasture. I am terrified now to turn my horses out, as it is autumn and the leaves are everywhere! Can you please tell me how many leaves they have to consume to be toxic? I have a feeling they have already eaten some of them, as I have had to stop them from eating acorns this year as well.

Yes, Red Maple leaves are toxic. However, usually this is when they are in the stressed state prior to dying (e.g. leaves on a fallen tree limb lying in a pasture). This is the point when the leaves are not only toxic but very tasty because they have stored a lot of sugar and are sweet and palatable. Once the leaves have fallen off the tree in the autumn they are dead and no longer palatable for the horses. By this point they will usually not hunt out leaves and consume them because the remaining grasses are much more palatable to them. If a horse consumes a few leaves here and there it is not enough to be a problem. However, putting an exact amount on what they need to consume is not possible either. No research has been done on this. However, clinical veterinary findings of poisoning cases usually directly involve downed tree limbs that have been cleared of all their leaves. It is advisable to make sure your horses have plenty of grass or hay or other forage to deter them from eating leaves or anything else they typically would not consume.

Can you tell me if tomato plants pose any hazard to donkeys? There is a wire mesh fence between my garden and my donkey pasture, but as you know, donkeys regard any barrier as a challenge to try whatever is on the other side.

Fruits such as tomatoes, which are healthy and enjoyable for us, actually pose a threat for horses and donkeys. The tomato plant is part of the Solanaceae plant family, which is toxic and includes potatoes, deadly nightshade, and horse nettle (referred to as wild tomato). The leafy and green portions of the tomato plants contain atropine, which slows the gut of the horse down. This causes colic in equids, which can be lethal. Hyoscyamine, also present in these plants, affects the nervous system. Hence, there is a decrease in saliva production, a decrease in the motility of the intestines and increased heart rate is also observed. The pupils begin to dilate as well. The hyoscyamine also has a direct effect on the digestive system, causing the equid to experience colic, as previously stated, constipation, and/or hemorrhagic diarrhea.

If the animal is displaying signs of muscle tremors, dilated pupils, and decreased intestinal motility, the animal may be treated with physostigmine. If the animal has been found right after the plants have been consumed, one may also orally administer activated charcoal, which will act as an adsorbent.

If adequate amounts of forage and well-maintained grass are available for them to eat, your donkeys should not consume any poisonous plants. During periods of drought, though, when lush grass may not be available for consumption, they may eat these normally unpalatable plants. To ensure that your donkey does not eat the tomatoes just make sure there is plenty of other grass or hay to eat. If they have that as an option they should not disturb the tomatoes in the garden.

Answer prepared by Stephanie Cruz, Animal Science Research Student at the School of Environmental and Biological Sciences, Rutgers University.

Can you please tell me how I can get a complete list, preferably with pictures, of plants that are toxic to horses? I want to put a barn with pastures on my property and want to make sure my property doesn't harbor any plants toxic to the horses.

There are many good references available on toxic plants. I have provided you with a list of my favorites below. Let me warn you that weeds and toxic plants are present on virtually every horse farm. I have worked on pastures on over 200 horse farms in Pennsylvania and New Jersey, and every one of them contained at least one species of toxic plants, shrubs, or trees.

The horse, as a species, has survived with toxic plants in its environment for a long time. Plants do not contain toxins in order to kill grazing animals. They are poisonous so that the animal will be exposed to the toxin, remember that the plant is not good to eat, and avoid it the next time. Toxins in plants generally taste bitter and sometimes have an offensive odor that causes animals to avoid browsing on them. Healthy animals that are well fed and have forage (hay and/or pasture) available to them rarely consume toxic plants. The most common reason for livestock poisoning is undernourishment. In early spring, late fall, or during periods of extended dry weather, animals may eat plants that they would not normally consume if other forage were available. Occasionally, individual animals may eat poisonous plants accidentally or when craving variation or special nutrients in their diet.

Below are several tips to assist you in reducing the risk of plant poisonings in horses.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

We just bought new land and are planning to build a three-stall barn, pasture and riding ring. Currently the property is wooded and we will have to clear many trees. The trees are large and beautiful so we would like to keep two to three to remain within the pasture area. I know that some of the trees are oaks because there are acorns all over the place, but we have to get the other trees identified. The trees will be fenced off, but my main concern is possible toxicity from leaves, acorns and other debris. What trees should we be concerned about?

Oaks are moderately toxic to horses. New young leaves and acorns, especially when green, are the toxic parts of the tree. The tannic acid in the acorns affects the intestinal lining and can cause portions of the lining to slough off. Symptoms of toxicity include poor appetite, weight loss, constipation and impaction followed by diarrhea, kidney failure and edema. In severe cases oak poisoning can lead to death.

It would be wise to remove all the trees from the pasture. Allow some trees to grow around the perimeter of the pasture for shade. Horses will usually girdle trees that they have access to, which will eventually kill them anyway. Also, no pasture grasses will grow well in the shade created by the canopies of the trees.

Other trees that you need to be concerned with include cherries of all species, red maple, horse chestnut, black walnut, and black locust.

Fortunately, plants with harmful toxins are designed to prevent animals from browsing and have a bitter taste that animals learn to avoid. Well-fed, healthy horses that have access to adequate forage, through pasture and/or hay, rarely consume toxic plants.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

Ornithogalum umbellatum has found its way into our horse pasture. Is it toxic? How do I get rid of it?

The plant that you refer to (Star of Bethlehem) is an ornamental that sometimes escapes into lawns and landscapes. It reproduces through the production of bulblets around the base of the main bulb and rarely produces seeds. It usually occurs in patches and rarely spreads through entire lawns.

I have never seen this plant occur to any great degree in pastures in New Jersey and Pennsylvania. Since it has been known to spread into lawns in this area, I would believe that it could be found occasionally in pastures. There are varying reports regarding toxicity of this plant. Although the plant itself contains alkaloids, there are reports of animals grazing on the plant without adverse effects. The small, white, onion-like bulb is toxic and sheep and cattle have died from eating the bulb. Symptoms of toxicity include salivation, depression, and gastrointestinal upset. It is believed that the toxic agent is a type of cardiac glycoside, which causes heart and digestive disturbances. The good news is that horses that are healthy and well fed rarely consume toxic plants, since the toxins have a bitter taste to discourage animals from browsing.

Star of Bethlehem is a cool season plant. It blooms very early in the spring and the leaves and blooms very quickly turn brown. Like other bulb plants (daffodils, tulips,etc.) the plants green -up and grow quickly in spring, send food reserves to the bulbs and then turn brown and die back. The only time to control the plant with an herbicide is when it is actively growing in early spring. Dr. Mark Van Gessel, weed specialist at the University of Delaware, suggests using fairly high rates of 2,4-D (1 quart per acre) where the plant is present in your pastures. In New Jersey and PA, you would need to apply the herbicide in early spring, since it will not translocate to the roots and bulb of the plant if the plant is dormant. Remember that 2, 4-D will also remove many other broadleaves from your pastures, including clovers. Before using pesticides, always read the label. Use pesticides only at the recommended time and rates. Be sure that the herbicide that you use is labeled for pasture use and adhere to any grazing restrictions. You may wish to contact a Crop Production Service to apply herbicides and fertilizers for you.

Answer provided by Donna Foulk, former Senior Agriculture Program Coordinator, Rutgers Cooperative Extension.

Yes, any species of Ligustrum or Privet is

Wax Leaf Ligustrum, also known as Japanese Privet (Ligustrum japonicum). Click for larger image.

poisonous to horses. Wax Leaf Ligustrum, also known as Japanese Privet (Ligustrum japonicum), is a deciduous shrub or small tree with small simple opposite leaves, which are lanceolate shaped and about 1 - 2 1/2 inches long. The leaves are dark green on the upper surface and a lighter green underneath. Some varieties may differ in leaf coloring, exhibiting white or yellow marbling. The white funnel-shaped flowers are small and numerous, appearing in terminal pyramidal clusters. These ripen into drooping clusters of blue to black wax-coated berries, which bear seeds. The toxin is thought to be andromedotoxin, however, most sources state the toxic principle is unknown. The most toxic parts are the berries and leaves. Signs of toxicity develop shortly after ingestion and range from gastrointestinal irritation with abdominal tenderness, diarrhea, hypotension, and renal damage. Ingestion may result in death within a few hours or after a day. Signs in nonfatal cases may persist for weeks. In one report, a case of colic continued for 37 days.

Answer provided by Carey Williams, Ph.D., Rutgers Cooperative Research and Extension.

My husband was clearing out a Wisteria plant, and he didn't think about the potential consequences of throwing the cut remains of the plants over the fence and into an area where our four horses could get to them. Now 3 of the 4 horses are acting funny, i.e. not wanting to eat. I am very worried about them. Could you tell me if Wisteria is poisonous to horses, and if so, what can I do about it?

It does appear that Wisteria is moderately toxic to animals and more toxic to humans. Some of the symptoms would include digestive upset, or colic, which is what sounds like your horses are suffering from. Hopefully your horses have not consumed a large amount of the plant, but you need to get them seen by a veterinarian.

In the future you can provide plenty of fresh hay and/or other feed to deter your horses from eating something they shouldn’t. Most horses will not consume toxic plants if given the option of other forage. Most toxic plants are unpalatable and give off a bitter taste and/or smell.

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