Datura : a poisonous plant

Datura or thornapple (Datura stramonium) is an upright annual herbaceous plant in the nightshade family (Solanaceae), with a foul smell. It is between 30 and 200cms high.

Leaves

Thornapple has large alternate leaves (laid out on either side of  the stem and  up to 30cms long) they are unevenly indented,  pointed at the extremity and hairless. They are a shiny dark green on the topside, lighter mat green on the underside. The main vein is clearly visible and raised on the underside, as are the secondary veins. The leaves also have a stalk which links them to the stem.

Flowers

The flowers blossom from June through to October, i.e. during summer to the beginning of autumn. Robust, ramified and with a smooth surface, the flowering stems have the particularity of splitting into two at each ramification (this feature makes the plant readily recognizable). At each of these ramifications a 10cm erect single flower develops at the leaf axil. These flowers are trumpet-shaped and either white or purple in colour.

Fruit

Thornapple fruit ripen at the end of Summer (August-September) through to late Autumn (sometimes as late as November). The fruit are thorny capsules (similar to chestnut or horse chestnut burrs) they are egg shaped, around 5cms long, green to begin, gradually turning brown and splitting into 4 valves when ripe. These valves contain numerous cross-linked black kidney-shaped seeds, measuring from 2 to 4 mm.

Thornapple is a plant species which originally came from Mexico and the South-west of the USA, and was introduced into Europe in the 17th century. It is widespread in France today, and is usually considered as a weed (undesirable species) in cultivated fields, as it invades cereal crops (corn, sorghum, buckwheat), oilseed and proteincrops (sunflower, soya) and vegetable crops (beans) harvested in autumn.

However the plant grows spontaneously in various different environments. It can therefore be seen in pastures, wasteland, rubble, uncultivated farmland, lane and roadsides… It is partial to newly overturned land

Even though Datura stramonium grows spontaneously as a wild plant, the Datura (or its close relative Brugmansia) genus is cultivated in parks and gardens, with horticultural varieties selected for their  colourful double or triple corollas, their pleasant scent or their majestic bearing. However, they are all poisonous to some degree and can sometimes escape their cultivated environment (Datura wrightii…). Finally, the plant is also sometimes used in potato culture as biological control against CPB larvae.

A poisonous but not very palatable plant

Datura plants are poisonous for a lot of mammals, including Man and Horse, as well as for some insects. « Devil’s weed », « hell’s bells » or « witches’ weeds »... some of the names which commonly refer to datura and to its toxicity.

The plant contains alkaloids - including scopolamine and atropine - toxic substances which cause neurological and heart disorders and induce paralysis of smooth muscle fibres when ingested, or even through the skin, in man and horses. The whole plant is toxic, but the alkaloid concentration is highest in the stem, the leaves and the seeds.

Fresh thornapple is unpalatable due to its unpleasant smell, thus horses will not usually eat it at pasture, but they can be poisoned in specific circumstances.

Poisoning which is frequently accidental

Even though the fresh plant is unpalatable, it becomes more easily consumable once dried in hay for example (loss of repulsive factors)

Intoxication usually takes place following accidental ingestion due to hay or hard feeds being contaminated by parts of the plant (especially the leaves or the seeds) or by seeds / leaves having fallen into short grass in the pastures.

More seldom, the fresh plant may be consumed, either when the animals are scraping around to find food during dry periods, or when bored, in deteriorated pastures, gardens or paddocks, or even when out (hacking or horse trekking...).

Clinical symptoms appear very quickly (a few hours) after ingestion. The severity depends on the quantity of toxic substances ingested, but intoxication can be fatal.

Following ingestion of this hallucinogenic plant, a horse will mainly demonstrate behavioural disorders and a neurological affliction, specifically with phases of depression/ lethargy interspersed by phases of hyper-excitability/  more or less severe convulsions  depending on the quantity ingested. These nervous symptoms can lead to dangerous behaviour which could lead to the horse becoming fatally endangered.

At the same time other symptoms may be observed :

• General symptoms : listlessness, hyperthermia, dryness of the mouth and eye mucus, mydriasis (abnormal pupillary dilation), polyuria, polydipsia (increase of urine emission and intake of water)
• Cardiovascular disorders : tahycardia (accelerationof the heartbeat)
• Respiratory disorders : tachypnea (acceleration of the breathing rate)
• Digestive disorders : constipation, gastrointestinal atony, sometimes diarrhoea and/or colic

Cutaneous exposure to the toxins usually leads to an attenuated clinical form compared to when ingested.

There is to date no specific treatment available for horses.

At the beginning of an intoxication, symptomatic treatment and  attempting to eliminate the toxin by gastric lavage and administering activated carbon or paraffin oil, associated with intravenous fluid therapy. Administering a sedative is also recommended to limit behavioural symptoms.

The only way to limit the risk of datura poisoning is knowledge of the plant, with an aim to achieve better control the environment in equestrian establishments and their close neighborhood, as well as watchfulness on the part of riders and horse owners. The plant should not be available to horses. To manage this :

• The species is invasive and extremely toxic both to Man and animals, it should therefore be banned from being planted in ground accessible to horses.
• Eliminate it where it is present. To do so there are several means :

Mechanical control⇒ If there are only a few plants, pulling them out by hand is a possible option. When the plant has colonized the environment, cutting the stems before seeding restricts the production of seeds. This is however a short term solution as other stems will grow back with more flowers. This type of intervention will therefore need to be repeated several times a year.

Chemical weeding should only be undertaken when necessary, in the case of an invasion, or when the plant is well established in the environment.  A chemical weedkiller for dicotyledons can then be used locally. By restricting the use of the weedkiller to the areas, or to the plants to be treated, local « plant by plant » treatment, is the best and technique, and is a more reasoned approach.

A key point in thornapple control is resticting seeding, as the plant has a considerable seed stock, seeds which can remain dormant several years in the soil.

• Avoid feeding (hay, hard feeds...) directly on the ground (prevention against datura seeds, sycamore samaras and other poisonous seeds, but also against mould and mycotoxins)
• Remain constantly alert :
  • When out hacking or at a show
  • Change of biotope (moving house…)
• Inform and raise public awareness ⇒  make sure riders and horse owners are aware of the risk.