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Identifying common poisonous pasture weeds

Pasture is a prime asset that sustains your livestock. However, dangers can lurk amongst the grass in the form of poisonous weeds that can make your livestock sick and possibly even kill them. Regular pasture walks to identify what is growing in your pasture is a good practice to get into. You need to be able to identify a potential threat plant and take action by removing it, by pulling it out or applying a spot treatment with herbicide. The Handbook of Toxic Plants of North America by George E. Burrows and Ronald J. Tyrl is a useful aid. Nonetheless, applying the principle of, "If in doubt, get it out," will do little harm. There are some poisonous weeds that you are more likely to encounter in your pasture than others such as:

Bitter Sneezeweed (Helenium amarum)
Classified as dangerous, the leaves stems, flowers, and fruit of the plant are poisonous. An annual, Bitter Sneezeweed grows between 10 to 20 inches high and has narrow leaves and will produce yellow, or yellow with a red-brown center flowers in the spring.

Black Nightshade (Solanum americanum)
Classified as dangerous, the leaves and unripe berries of the plant in particular have been known to poison livestock and pets. The plant can grow up to five feet in height and has alternate leaves up to nearly four inches long and over two and a half inches wide. The flowers are white or sometimes light purple with a yellow stamen; the berries are shiny and black when ripe.

Bracken Fern (Pteridium aquilinum)
Classified as dangerous, Bracken Fern has triangular fronds with multiple stems; the plant can grow up to four and an half feet in height.

Coffee Senna (Cassia occidentalis)
Is a weakly toxic plant that has been known to affect cattle in particular. Coffee Senna has a stem up to 12 inches long with 8 to 12 leaflets positioned opposite one another along the leaf; Coffee Senna produces half inch to three quarter inch long yellow flowers.

Common Cocklebur (Xanthium strumarium)
Classified as dangerous for its seeds and seedlings, Common Cocklebur can grow up to six and half feet high and has irregular triangular leaves from two to six inches long with three large veins on the top of the leaf; the plant produces prickly cocklebur seed pods.

Crotalaria (Crotalaria spectabilis)
Classified as dangerous, the leaves, stems, roots, and seeds are poisonous. The plant is an annual with yellow flowers and alternate two to six inch long leaves that are hairless on the top of the leaf but with hairs lying flat on the underside.

Groundsel (Senecio)
A suspect in the poisoning of cattle and horses, Groundsel is an annual or a year-round plant in areas of California. The plant can grow up to two feet high with alternate leaves along the stem culminating in a cluster of yellow flowers; the lower leaves have a short stalk.

Hemp Dogbane (Apocynum cannabinum)
The leaves of this plant are toxic and a horse or cow can die from eating just a small amount of it. This perennial, which can grow up to six feet in height, has shiny ovate or elliptic leaves with few hairs on the underside; the leaves and stem secrete a milky sap when broken.

Hemp Sesbania (Sesbania exaltata)
The seeds of this plant are dangerous. Hemp Sesbania grows between three feet to six feet in height. Each leaf has up to 70 leaflets and the plant has yellow (sometimes spotted or streaked with purple) flowers and distinctive seed pods between four to eight inches long.

Horsenettle (Solanum carolinense)
The berries and leaves of the Horsenettle plant are poisonous. The plant can grow up to three feet in height and has oval/oblong looking leaves that are covered in fine hairs. The flowers are usually white or purple with yellow centers that produce tomato-like berries.

Jimsonweed (Datura stramonium)
Also known as, Thornapple, stinkweed, and locoweed, all parts of Jimsonweed are poisonous with the seeds in particular being more potent. The plant can grow up to five feet in height and has white flowers and forms prickly seed pods.

Mustards (Brassica)
All parts of these annual broadleaf weeds are toxic. In younger plants, look for bright green leaves that are paler underneath. The mature weed can reach a height of five feet and will have dense clusters of bright yellow flowers and the ends of its branches.

Perilla Mint (Perilla frutescens)
The leaves and stems of the plant are dangerous and can often be tempting to livestock during dry spells. The plant is an upright herb, growing up to two feet in height, with green or purple-green leaves that emit a mint-like odor.

Pokeweed (Phytolacca americana)
The roots, shoots, leaves, and berries of Pokeweed are dangerous, with the roots being the most potent. The plant can grow up to ten feet high with up to five-inch long leaves; Pokeweed berries turn from deep red to purple when they are ripe.

Sicklepod (Cassia obtusifolia)
This plant is designated as weakly toxic but could make your livestock sick. Sicklepod can grow from one foot to six feet in height; the leaves are egg shaped and the plant produces a four to eight inch long brownish colored seed pod.

Smooth Pigweed (Amaranthus hybridus)
All parts of this plant are poisonous and ingestion can result in cardiac arrest between five to ten days after eating it. Look for a green to reddish stem on a plant up to five feet high. The leaves are long stalked and oval to diamond shaped; the plant’s flowers are usually green and small.

White Snakeroot (Eupatorium rugosum)
A perennial herb, all parts of White Snakeroot are poisonous. The branched plant can grow up to five feet high but usually is around three feet tall. The three to five inch long leaves have three veins; the plant develops clusters of small white flowers at the end of the branches in summer.



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