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Poisonous Plants and Pets

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OAKS (Quercus spp.)OAKS (Quercus spp.) – Oak species are commonly recognized by their leaves, thick bark, and cupped fruit (acorns). Leaves of many species are characteristically lobed while some have toothed leaves, except for the shingle and willow oaks, whose leaves are entire rather than lobed or toothed. Oaks are common in woodlands throughout Ohio.

Most species of oak contain toxic phenolic compounds (tannins). Large quantities of young leaves and sprouts are toxic when consumed in spring as are green acorns in the fall. Poisoning occurs when over half the diet is oak buds and young leaves, or acorns, for a period of time. Livestock have also been poisoned by drinking water in which oak leaves have soaked. Plant tannins or their metabolites cause gastrointestinal and renal dysfunction. Symptoms appear several days after the period of consumption and include abdominal pains, weakness, anorexia, colic, constipation, depression, diarrhea, presence of blood in urine, and jaundice. Death may result. Horses are less susceptible than ruminants. Oak poisoning resembles pigweed poisoning.


BUCKEYE (Aesculus spp.)BUCKEYE (Aesculus spp.) – Several species of buckeye can be found in Ohio and are distinguished by opposite palmately-compound leaves (with five- to seven-toothed leaflets per leaf) and large glossy brown seeds with a whitish scar. Two species are native woodland trees, the Ohio buckeye (A. glabra) and sweet (or yellow) buckeye (A. octandra). The Ohio buckeye is widely distributed throughout the state, while sweet buckeye is confined to southern Ohio. Other buckeye tree and shrub species can be found in cultivation, including horse chestnut (A. hippocastanum).

Toxicity of buckeye is attributed to glycosides (e.g., aesculin, fraxin), saponin (aescin), and possibly alkaloids. Sprouts and leaves produced in early spring and seeds are especially poisonous. However, experimental feedings have shown that poisoning does not always follow buckeye consumption. Affected animals exhibit depression, incoordination, twitching, paralysis, inflammation of mucous membranes, and vomiting. Colic has also been reported in poisoned horses. Treated animals usually survive.

In the spring, while waiting for other forage to become available, animals should not be allowed to graze in woodland pastures where there are buckeye sprouts.


RED MAPLE (Acer rubrum)RED MAPLE (Acer rubrum) – Red maple is a large native tree found in moist woodlands and swamps throughout Ohio. Leaves are opposite, generally triangular with three or five lobes, coarsely toothed, and silvery white beneath.

Poisonings result from consumption of wilted leaves and have only been reported for horses. Toxicity is most prevalent from June through October, but may be greatest in autumn foliage. Dried leaves are reported to remain toxic for 30 days. The cause of toxicity is not known. Primary effects are acute hemolytic anemia, methemoglobinemia, and Heinz body formation in the red blood cells. Symptoms develop three to four days after ingestion of leaves and include rapid breathing and heart rate, weakness, depression, jaundice, cyanosis, brownish discoloration of blood and urine, coma, and death.


BLACK LOCUST (Robinia pseudoacacia)BLACK LOCUST (Robinia pseudoacacia) – Black locust is a naturalized species that grows as a tree or shrub in open woods, waste places, and along fence rows throughout Ohio. Leaves are alternate and are pinnately compound, with more than 10 leaflets per leaf. A pair of spines occurs at the base of each leaf. White flowers appear in loose drooping clusters in May or June and later form long flattened brown seedpods.

Several toxic compounds are found in black locust sprouts, leaves, bark, flowers, and seed pods, including a glycoside (robitin) and phytotoxins (robin and phasin). Of grazing animals, horses are most susceptible to the effects of black locust. Poisoning and death have been reported for horses consuming bark, leaves, or sprouts. Livestock have also been poisoned by drinking water in which seedpods have soaked. Affected animals often stand with feet spread apart. Other signs include depression (often extreme), diarrhea, anorexia, weakness, posterior paralysis, colic, pupil dilation, coldness of extremities, laminitis, weak pulse, and rapid, irregular heartbeat. In severe cases, death can result from cardiac failure.


BLACK WALNUT (Juglans nigra)BLACK WALNUT (Juglans nigra) – Black walnut is a large tree growing in rich forest soils throughout Ohio. Leaves are alternate and are pinnately compound with numerous toothed leaflets. The twigs have a characteristic chambered pith. Black walnut fruits consist of a nut surrounded by a thick husk and do not split open when ripe.

The toxic phenolic compound, juglone, is found in the bark, wood, nuts, and roots of black walnut. Horses are primarily affected when exposed to shavings that contain black walnut wood. Shavings contaminated with less than 20% black walnut can cause poisoning in 24 hrs. Affected horses exhibit depression, lethargy, laminitis, distal limb edema, and increased temperature, pulse, respiration rate, abdominal sounds, digital pulse, and hoof temperature. Consumption of the shavings may also cause signs of mild colic. Symptoms usually disappear within a few days after shavings are removed.

Horses on pasture may show mild respiratory signs from pollen or fallen leaves.


YEWS (Taxus spp.) YEWS (Taxus spp.) – Yews are evergreen shrubs characterized by linear leaves that are glossy dark-green above and yellowish-green below with a distinct mid rib, and by fruit consisting of a single seed within a bright red fleshy cup-shaped structure resembling a berry. Leaves are alternate and are spirally arranged along the twig, although they appear to be in two rows. One native species of yew grows in Ohio, the Canada yew (or ground-hemlock) (T. canadensis). It is patchily distributed throughout the state and is most common in the northeast. Many cultivated species are used as ornamentals, including Japanese yew (T. cuspidata) and English yew (T. baccata).

Leaves, bark, and seeds (but not the fleshy pulp) of yews contain alkaloids (taxine) that affect the nervous system and are toxic whether green or dry. In small quantities, yew may be harmless. Canada yew is heavily browsed by deer. But when large quantities are eaten, death may follow rapidly due to cardiac failure, with few preceding symptoms. Poisoning often occurs when clippings are placed where they are accessible to animals. Symptoms include gaseous distress, diarrhea, vomiting, tremors and convulsions, dilated pupils, respiratory difficulty, weakness, collapse, slowed heart rate, circulatory failure, coma, and death.


MOUNTAIN LAUREL (Kalmia latifolia)MOUNTAIN LAUREL (Kalmia latifolia) – Mountain laurel is an evergreen shrub characterized by glossy leathery dark-green leaves and showy white to pink flowers formed in dense terminal clusters. The shrub occurs mostly in the southeastern portion of Ohio, where it grows in hillside woodlands and pastures.

All parts of mountain laurel, including leaves, twigs, flowers, and nectar (as well as honey made from it), contain a toxic resinoid (andromedotoxin); leaves and twigs also contain a cardiac glycoside (arbutin). Affected animals may exhibit incoordination; watering of the eyes, nose, and mouth; irregular breathing; vomiting; bloat; weakness; convulsions; coma; and death. Poisonings occur most often in winter or early spring when other green forage is not available. Horses are susceptible to poisoning; however, sheep poisonings are reported more frequently, since mountain laurel grows on land more suited for sheep.


PRIVET (Ligustrum spp.) PRIVET (Ligustrum spp.) – Privet species are introduced semievergreen or evergreen shrubs commonly used as ornamental shrubs or hedges. They are characterized by small opposite leaves, white flowers, and hard black berrylike fruits that persist through winter. One privet species (L. vulgare) frequently escapes cultivation in Ohio and is well scattered throughout the state. It may be found in woods and bottomlands, at abandoned home sites, and along fence rows.

Leaves and fruit of privet contain several toxic glycosides (e.g., ligustrin, syringin) which are primarily gastrointestinal irritants. Poisonings have been reported for horses eating privet leaves. Symptoms include diarrhea, abdominal pain, incoordination, partial paralysis, weak pulse, hypothermia, convulsions, and sometimes death.


WILD BLACK CHERRY, CHOKE CHERRY, AND PEACH (Prunus spp.) WILD BLACK CHERRY, CHOKE CHERRY, AND PEACH (Prunus spp.) – Many species of cherry and peach are poisonous. These species are characterized by alternate toothed leaves, white or pink flowers, and fleshy fruits (cherries or peaches). Crushed twigs and leaves yield a strong cyanide odor. Two native species of cherry are common in Ohio. Wild black cherry (P. serotina) is a large tree that is distributed widely throughout the state in woodlands, old fields, and along fence rows. Choke cherry (P. virginiana) grows as a large shrub or small tree and is scattered throughout Ohio in a variety of habitats, though it is more frequent northward. Peach (P. persica) is a small introduced tree that occasionally escapes from orchard cultivation through seed.

Seeds, twigs, bark, and leaves contain a glycoside (amygdalin) that quickly breaks down by hydrolysis (from bruising, wilting, frost damage) to form the highly toxic compound hydrocyanic (prussic) acid (or cyanide). Poisonings occur most frequently when wilted leaves are eaten, but have also been reported when leaves are consumed directly from the tree, or sprouts, or in dried hay. The amount of hydrocyanic acid formed once the plant material is ingested is affected by the type of stomach juices and the kind of feed the animal had previously consumed. Ruminant animals appear to be more susceptible to poisoning than horses.

Cyanide poisoning results in hypoxia (deficiency of oxygen reaching the tissues). The first symptoms appear within a few minutes following consumption of plant material. Affected animals exhibit excitement, incoordination, convulsions, rapid and labored breathing, bloating, and coma. Death can occur in less than an hour due to internal asphyxiation.