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Plants Poisonous

and Harmfulto Horses

Krishona Martinson, PhDEquine Extension Specialist

University of Minnesota

Meet our presenters:

Krishona Martinson, PhD

Equine Extension Specialist

University of Minnesota

Roger Becker, PhDExtension Weed

SpecialistUniversity of Minnesota

Outline•Introduction

•Poisonous and Harmful Plants

•Weed Control

•Steps to Minimize Poisonous Plants

Introduction•Weed – a plant growing out of place

•Invasive – a weed capable of displacingexisting plants; This is a concern especiallywhen non-native weeds invade nativeecosystems.

•Noxious – on a State or County noxiousweed list

Introduction•Weeds are generally:

• Less palatable• Less nutritious• Lower yielding• Less dependable as a forage• Invasive• Poisonous• On the noxious weed list

Introduction•Most toxicity is seen in the fall or during a drought when feed is short

Outline•Introduction

•Poisonous and Harmful Plants

•Weed Control

•Steps to Minimize Poisonous Plants

Annuals – 1 year to complete lifecycle•Foxtail

•Eastern Black Nightshade•Common Cocklebur•Weed Seeds

•Weed Control – mowing and herbicide (if needed) in spring•Always read and follow label directions

Foxtail (Seteria species)•Annual

•Causes physical trauma to the oral cavityand GI tract

•Lip or tongue ulcers

•Hay/pasture would be less than 10% foxtail

•No selective herbicide options in grass pasture

Tickle Grass (Agrostis hyemalis)

Embedded in horse’s mouth

Eastern Black Nightshade (Solanum ptychanthum)•Annual

•Ingestion of 0.5% to 1% bodyweight can be toxic

•Affects GI tract

•Clinical signs include colic

•Broadleaf herbicides – 2,4-D andor Dicamba

Common Cocklebur (Xanthium stumarium)•Annual

•Stems are hairy, rough to the touch andReach 2-4 feet tall. The leaf surface ishairy and rough to the touch.•The fruit is a 2-seeded bur covered withHooked spines. Burs easily becomeTangled in horse manes/tails.•Cocklebur can be poisonous to allanimals, especially cattle and hogs.•Can be controlled mechanically by hand-pulling and chemically by Stinger

Common Cocklebur (Xanthium stumarium)•Cocklebur seedlings can be poisonous

to all animals, especially cattle and hogs.

•Can be controlled mechanically by hand-pulling and chemically by clopyralid.

Common Cocklebur (Xanthium stumarium)•Conditions of poisoning occur most often

in early spring (2-8 leaf stage)

•0.25% body weight (2.5 pounds)

•Affects liver

•Clinical signs include colic and death

Mustards (Brassica species)Corn Cockle (agrostemma

githago)•Problems occur when horses ingest weedseeds in oats or sweet feed•Affects GI tract and clinical signsinclude colic•Don’t use “field/bin run” oats thathave not been cleaned

Biennials – 2 years to complete lifecycle•Poison Hemlock

•Wild Parsnip

•Weed Control – mowing (difficult in first year) and herbicide application (if needed) in first year•Always read and follow label directions

Poison Hemlock (Cornium maculatum)•Plants can reach heights of 2-7 feet tall

•Stems have purplish spots

•Leaves have a lacy appearance

•Flowers are white and are shaped likeumbrellas

Poison Hemlock (Cornium maculatum)•Found in wet sites or along streams

•All parts of plant are very poisonous to allanimals when eaten fresh and in dried hay

•Seeds are especially poisonous

•Broadleaf herbicides – Dicamba and/or 2,4-D

Wild Parsnip (Pastinaca sativa)•Stem is somewhat hairy, grooved, and2-5 feet tall

•Leaves are course, with saw-toothededges

•Flowers are yellow, and arranged in anumbrella shape

Wild Parsnip (Pastinaca sativa)•Found in fields and along roadsides,and occasionally in wet pastures

•If pulling by hand, wear gloves andprotective clothing, as contact can causesevere blistering of the skin

Wild Parsnip (Pastinaca sativa)•May contain furanocoumarins

•Severe sunburn may occur throughskin contact, or in the blood vesselsdue to ingestion

•Severe sunburn reduced if shadedfrom sunlight

Wild Parsnip (Pastinaca sativa)•Broadleaf herbicides – Dicambaand/or 2,4-D

•Apply in first year’s growth or insecond year’s growth prior toflowering

Perennials – Survives 3 or more years•Waterhemlock

•Hoary Alyssum•White Snakeroot•Buttercup (Tall)•Horsetail•Brakenfern

•Weed Control – mowing and herbicide application (if needed) in the fall (prior to flowering)•Always read and follow label directions

Waterhemlock (Cicuta maculate)•The small white flowers are borne inflat-topped, umbrella-like clusters atthe tips of stems and branches

•Found in swampy areas and marshes,wet meadows and pastures, and alongstream banks and low roadsides

Waterhemlock (Cicuta maculate)•Toxicity decreases through thegrowing season, and the toxicity ofabove-ground parts may be negligiblewhen dry

•The roots are toxic at all times, evenwhen dry

•Only 8 ounces will kill a horse

Waterhemlock (Cicuta maculate)•Signs will develop within an hour, and includenervousness, and dilated pupils, muscle tremors,difficulty breathing, falling down andconvulsions

•Death, may occur within 30 minutes of theonset of signs

•Broadleaf herbicides: Dicamba and/or 2,4-D

Hoary Alyssum (Berteroa incana)•Some horses experience depression, fever, and"stocking up," or swelling of the lower legs,12 to 24 hours following ingestion

•These clinical signs normally subside 2 to4 days following removal

•Hoary alyssum is mostly a concern in hay

Hoary Alyssum (Berteroa incana)•Severe symptoms have been observedin horses ingesting hay containingmore than 30% hoary alyssum

•Toxicity is variable and approximately45% of horses do not seem to react

Hoary Alyssum (Berteroa incana)•Death has not been observed

•Founder can be an issue with prolongedingestion or when stressed

•Hay containing hoary alyssum shouldnot be fed to horses

White Snakeroot (Eupatorium rugosum)•Plant reaches heights of 1 to 3 feet

tall

•Leaves have toothed edges andflowers are white

•Found only in shady areas

•1 to 10 pounds of plant material isthe toxic dose

Buttercup (Ranunculus species)•Affects lower GI tract and blisteringof lips and mouth

•Clinical signs include colic

•Mechanically controlled by handpulling. Chemically controlled byBanvel and MCPA

Field Horsetail (Equisetum arvense)•Stems are tough and wiry, hollow and jointed

•Found mostly on wet, sandy soil

•It is poisonous to livestock when eaten in largequantities

•Chemically controlled by Roundup (spot treatmentonly) or Triclopyr. Use caution when spraying near awater source.

Bracken Fern (Pteridium aquilinum)•Plant grows 1 to 4 feet tall

•Found in open pastures, woodlands andparticularly on acid soils (under pine trees)

•Conditions of toxicosis occur if ingestionfor 30 or more days as 20% or more of thediet

Bracken Fern (Pteridium aquilinum)•Affects brain and clinical signs include seizures

•Mechanically controlled by frequentmowing. Chemically controlled by Ally(spot treatment only)

Ornamentals•Yew•Foxglove•Rhododendron•Oleander

•Control – avoidance and species removal

Japanese Yew (Taxus cuspidata)•Avoid introducing as landscapeornamentals in proximity to horses

•Do not put clippings into pasture

•Do not put yew wreathes on boxstall doors

•Can cause death

Foxglove (Digitalis sp.)Rhododendron (Rhododendron

sp.)Oleander (Nerium oleander)•Avoid introducing foxglove, rhododendron, oleander as

ornamentals in proximity to horses

•Most are associated with overgrown or escaped landscapes

•All can cause death

Foxglove, Rhododendron & Oleander

Woody Species•Chokecherry•Black Walnut•Maple•Oak

•Control – avoidance and species removal

Chokecherry (Prunus virginiana)• Chokecherry bark, leaves and seeds are

poisonous

• Damaged leaves pose the greatest risk

• Do not plant around horses

• Cyanide is the toxin

• Clinical signs include anxiety, breathingproblems, staggering, convulsions, collapseand death

Black Walnut (Juglans Nigra)•Toxicosis includes using the shavings forbedding

•Affects the vascular organs

•Clinical signs include stocking up andfounder

•Do not use dark shavings for bedding

Maple (Acer species)•Ingestion of 1 to 3 pounds of wiltedleaves per 1,000 pound horse (Fall orSummer Storm)

•Signs of toxicosis include colic and/orred/brown urine

•Affects red blood cells and the liver

Oak (Quercus species)•Most species of oaks can cause livestockpoisonings

•Ingestion of LOTS of acorns with greenhull still attached

•Affects the kidney (tannins)

•Clinical signs include colic

Photo Credit: ACC-CTC

Grazing Precautions•Endophyte Infected Fescue

•Clovers

Endophyte Infected Fescue•Can cause dry gangrene in feet and ears(restriction of blood flow), prolongedgestation, no/reduced milk production(agalactia)

•Prevention: plant “endophyte free” fescue

Moldy Sweetclover (Melilotus species)•Harvested for hay AND hay gets moldy.

•An unknown mold converts the naturally occurringcumarol in the sweet clover to dicumarol

•Horses may bleed if moldy sweetclover hay is asubstantial amount of a horse’s diet

•Injections of vitamin K or blood transfusions(extreme bleeding situations)

Moldy Sweetclover (Melilotus species)•Can cause slobbers

•Infestation of red clover with a mold(upper side of leaves) in hot humid weather(usually > 85 F)

•Access to water and remove horses frommoldy clover pasture

Clover (Melilotus and Trifolium species)•Can cause sunburn when infestation with

mold (underside of leaves)

•Can cause liver damage

•Move out of the sun, topical cream,check liver

Weed Control•A healthy, dense pasture will out-compete most weeds

•Herbicides alone will not result in a weed-free horse pasture

•If using an herbicide, make sure to follow the label and grazing restrictions

Weed Control•Cultural Control• Do not over-graze• Over-seed thin areas• Fertilize

•Mechanical Control• Mowing

•Chemical Control• Herbicides

Steps to Minimize Poisonous Plants1. Avoid over-grazing pastures

2. Rotate and rest your pastures3. Mow after grazing (>4”)4. Remove horses from pasture during drought

(scout your pastures)5. Thick, well-managed pasture will choke out

weeds6. Herbicides alone will not result in a weed-free

pasture7. Learn to identify poisonous plants

ReferencesMartinson, Hovda, and Murphy. 2007. Plants Poisonous or Harmful to Horses in the North Central United States (www.extension.umn.edu/horse)

Martinson and Peterson. 2007. Managing Established Horse Pastures. (www.extension.umn.edu/horse/components/pasture.htm)

Cornell Poisonous Plant Website (www.ansci.cornell.edu/plants/horselist.html)

Questions?

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