Beware of poisonous plants under dry pasture conditions

Under more typical rainfall conditions, cattle usually avoid poisonous plants because they taste bitter and better feed is only a swing of the head away. But when the speed at which pastures recover from grazing under dry conditions gets slow, animals have to look harder for adequate vegetation, the risk of livestock poisoning from poison plants increases. Below we talk about several species to watch for before animals are lost.

Water Hemlock

We have received several calls about spotted water hemlock (Cicuta maculata), which is a native member of the carrot family, common in Saskatchewan and likes to grow in the saturated soils of low swampy areas. When the larger pasture areas dry out, cattle concentrate on these moister areas where vegetation is still lush and this is where the danger lies. Cattle have only bottom teeth, meaning they tend to pull on forages to feed, rather than nipping plants off cleanly like horses and sheep. Spotted water hemlock is so shallow rooted, making it easy for cattle to pull completely out of the ground, root and all. Even sheep and horses can pull them out of the ground unintentionally and consume all or portions of the plant. Spotted water hemlock and other related hemlock species, have many-chambered bulbs at the base of the stem, (crown) that contain an oily amber-coloured fluid that is highly poisonous. Should an animal get hold of and consume one of these bulbs, death is quick and painful, as the amber liquid is an acute nerve toxin. Animals progress quickly from excessive salivation and twitching to violent seizures, vigorous biting at the air, followed by coma and then death.

The occasional plant can generally be easily grubbed out manually using a shovel and the entire plant removed from the site. For larger infestations MCPA 500 Amine at 0.89 L per acre in 40 litres (10 gallons) of water per acre is the registered option for controlling water hemlock. 2,4-D 600 Amine will also control water hemlock at 0.61 to 1.6 L per acre in 40 to 120 litres (10 to 30 gallons) of water per acre, but there is also a risk of hard water antagonism with 2,4-D amine that isn’t there with MCPA. If there are any legumes in the stand, MCPA will protect them too whereas 2,4-D will likely injure them. These products cannot be applied directly to or within one metre of standing water. Ester formulations are not registered for control of water hemlock.

Following application of herbicides, the spotted water hemlock plants should be completely browned off before allowing livestock into the area and this will likely take withdrawal periods after applications well beyond the seven-day grazing restriction period. If livestock are allowed into the treated area before the water hemlock plants are completely browned off, they can be more palatable to livestock while still green/yellow, increasing the risk of poisoning. If there is a water body associated with the plant that the livestock may drink from, producers need to be aware that trampled water hemlock bulbs leaking poison sap into the water, that was later drunk by livestock, have been implicated in livestock deaths as well.

Water hemlock gets about four feet tall and has several white umbrella-shaped flowers. Leaves are double compound and roots are comprised of tubers that have several chambers with oily yellow liquid in them that is highly poisonous.

Humans exposed to the sap can suffer similar symptoms to livestock. Sap can be absorbed through contact with the mouth, skin and eyes. Children using the hollow stems of water hemlock as pea shooters have also died from oral exposure. When handling this plant, make sure that all skin is protected by impenetrable clothing and wear full goggles to protect the eyes. Protective clothing should be discarded or thoroughly washed after work with the water hemlock is completed.

Cherries

Chokecherries are a common plant whose leaves can produce cyanide in ruminant livestock like cattle, sheep and goats.

Chokecherries (Prunus virginiana), pin cherries (Prunus pensylvanica), sandcherry (Prunus pumila) or other members of the plum family may contain compounds in their foliage that rapidly convert to cyanide in the rumens of cattle, sheep and goats. Monogastrics like horses and pigs are less inclined to this type of poisoning because of their acid stomachs do not convert the compounds to cyanide as easily or quickly. However, they can become poisoned if they consume vegetation that has been trampled or injured and allowed natural enzymes to convert the compound to cyanide. Cyanide poisoning results in rapid onset of symptoms that include salivation, agitation, muscle tremors, rapid breathing as though trying to catch its breath, loss of continence, epileptic-like seizures and then death. Removal of any accessible plants using mechanical methods is the most straight forward approach since it is the foliage that is toxic. Herbicide options can be found in the “Special Weeds” section of the Guide to Crop Protection.

Milkweeds, showy milkweed (Asclepias speciosa) being the most common in Saskatchewan, can cause poisoning if foliage is consumed. Broad-leaved milkweeds, which are the predominant type here in Saskatchewan, contain cardiac glycosides that can cause gastric distress as well as heart arrhythmia both speeding and slowing of the heart that can result in low blood pressure and dizziness (too slow) or heart failure or stroke (too fast) as well as an excessive loss of body heat (hypothermia). The toxicity of the cardiac glycosides found in milkweeds is not lost or denatured when harvested for hay so toxicity can occur in winter months as well.

Milkweed can be controlled by dichlorprop-P based herbicides like Estaprop XT or Dichlorprop-DX at 1.11 L per acre in 80 to 240 litres per acre of water. Treated areas must not be grazed by livestock or cut for hay for 40 days after application.