The larkspurs are divided into three groups: the tall larkspurs (D. barbeyi, D. occidentale), the low larkspurs (D. nelsonii), and the plains larkspurs (D. geyeri), based on their height at maturity and geographic location.
Tall larkspurs have a spurred blue flower, similar to that of garden delphinium. Broad leaves are divided into deep lobes. In contrast, wild geranium, which is often mistaken for larkspur, has shallow leaf lobes. Tall larkspur is a perennial that is found on hillsides and in meadows. It ranges in height from 1 to 2 meters. A hollow stem distinguishes larkspur from poisonous monkshood, which has a similar blue flower but with a hood.
Low larkspur has spurred blue flowers that grow on the top third of a single and unbranched stem. It is found on grassy hillsides and in sagebrush areas, where it may reach a height of 2 feet. Leaves alternate and are divided into deep, narrow lobes. The stem is hollow.
Where and When It Grows
Tall larkspurs tend to grow on deep soils where a plentiful supply of moisture is available and at higher elevations (above 7000 feet). They grow in mountain meadows on sites where deep snowdrifts persist well into the growing season, under aspens on north-facing slopes, along streams, or around seeps and springs. Tall larkspurs begin growing as soon as the snow melts, but at the upper limits of their distribution this may not occur until July.
Low larkspurs tend to grow at lower elevations (and higher elevations with tall larkspurs) where they grow, mature, and become dormant before the soil moisture is depleted. They begin growing in early spring, often before other forage begins growth. Low larkspurs are most palatable to cattle after flowering.
Plains larkspurs are found primarily on the high plains of Colorado, Wyoming, and New Mexico. Cattle may eat plains larkspurs at any stage of growth. Both low and plains larkspurs begin growing in early spring, often before grasses start their spring flush of growth. Under these conditions, larkspur may be the only green herbage available to cattle.
How It Affects Livestock
Larkspur causes heavy cattle losses in western range states. Larkspur is highly palatable to cattle, and losses can be expected when cattle are allowed to graze larkspur-infested ranges, especially where the plant is abundant or grows in large, dense patches. Tall larkspurs increase in palatability as plants mature. Cattle consume larkspur most often after plants begin flowering; consumption increases into the pod stage. Rain, cold fog, or snow showers may lead to greatly increased consumption of larkspur.
Losses rarely occur in sheep or horses, but if subjected to sudden physical activity after ingesting large amounts of larkspur, these animals may die. Plants are most toxic during early growth, but toxicity gradually declines over the growing season. However, toxin levels may increase in the flowers and pods even late in the season. The toxic substances are mixtures of several alkaloids. These alkaloids and their relative toxicity and concentrations vary between individual plants, at different locations and between larkspur species. The method of toxicity has been identified as neuro-muscular paralysis, leading to respiratory failure, bloat and often death.
All parts of all larkspur species are poisonous, but new growth and the seeds contain the highest concentrations of toxic substances.
Signs and Lesions of Poisoning
Weakness and staggering gait; animal may fall suddenly
Nausea and vomiting may occur
Bloating may occur
Rapid, irregular pulse
Animal may die
Excitement and physical exercise intensifies all signs of poisoning
Minimal gross lesions (bloat and pulmonary congestion)
How to Reduce Losses
There is no proven treatment for larkspur poisoning. It has been suggested that poisoned animals be treated with cholinergic drugs such as physostigmine or neostigmine. Though such treatment can reverse some of the clinical changes, their effects on larkspur’s lethal effects are unproven. It may be that the stress and excitement of treatment outweigh any beneficial therapeutic effects. Currently conservative therapy such as placing an affected animal on its brisket or chest with its head uphill to reduce bloating and treating bloat are recommended. Most important is to avoid unduly exciting affected animals until they can clear the larkspur toxins.
Larkspur in its early vegetative growth stage is not palatable, therefore grazing early before plants flower may be a useful option in some areas. Once plants begin flowering, keep cattle off ranges until the plants mature, then allow them to graze larkspur areas after the pod stage when toxicity is low. Using sheep to graze or trample larkspur patches ahead of cattle grazing may also reduce cattle losses. Aversion conditioning can be used to condition cattle to avoid eating larkspur and may be practical if persistent losses occur.
Do not graze cattle on larkspur ranges treated with herbicide until larkspur is senescent in the fall. Herbicide treatment may increase palatability to cattle, but does not lower larkspur toxicity.
Research results show that low larkspurs can usually be controlled by applying 2,4-D at the rate of 2 kg ae/Ac when the vegetative development approaches its maximum but before the first flowers open.
Tall larkspur can be controlled with picloram (0.5 - 1.0 kg ae/Ac) up through the flowering stage. Metsulfuron (30-40 gm ai/Ac) is effective as a spot spray when applied in the early vegetative and bud stages of growth. Follow precautions when handling herbicides.