Tall larkspurs tend to grow at higher elevations on deep soils where a plentiful supply of moisture is available. 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 larkspur begins growing as soon as snow melts, but at the upper limits of their distribution this may not occur until July.

Low larkspurs tend to grow at lower elevations where they mature and become dormant before the soil moisture is depleted. They begin growing in early spring, often before other forage begins growth. Low larkspurs grow best when springs are cold and wet. Cattle will graze low larkspur at all stages of growth, but most often graze it after flowering.

Plains larkspur is found primarily on the high plains of Colorado and Wyoming. It begins growth in spring before other plants.

How larkspur affects animals:

Plains larkspur may be eaten by cattle at any time during summer, but early green growth and pods may be most appealing to cattle. Both low and plains larkspurs may be the only green herbage available to cattle in early spring.

The larkspurs contain a number of alkaloids of varying toxicity. The most toxic of these are the MSAL (methyl succidimino acetyl lycoctonine) types, which include methyllycaconitine. Submit a sample to the Poisonous Plant Research lab for analysis.

How to reduce loss:

Placing an af­fected animal on its brisket or chest with its head uphill may reduce bloating. Treatment for bloat (intubation or rumen puncture with a trocar) may save some animals. Avoid unduly exciting affected animals.

Toxicity of tall larkspurs declines as it matures through the growing season. Research has identified a toxic window of high risk during the flower and early pod stages when it becomes palatable and toxin levels are moderate.

Since cattle do not generally consume tall larkspurs before flowering, grazing early before plants flower may be an acceptable grazing option. Cattle should be moved off of the larkspur areas during the flower stage but can graze larkspur in the late pod stage when toxicity declines. Using sheep to graze or trample tall larkspur patches ahead of cattle grazing may reduce cattle losses.

Low larkspur losses may be prevented by deferring grazing until plants lose their flowers and pods, as they rapidly senesce after producing pods. This usually occurs in late spring or early summer and grazing is safe after seed shatter.

The cholinergic drug neostigmine (0.02 mg/kg i.m.) has been successfully used under pen conditions to reverse clinical larkspur intoxication. This reversal lasts about 2 hours, and repeated injections of neostigmine are sometimes required. Under field conditions, neostigmine temporarily abates clinical signs and animals quickly (about 15 minutes) become ambulatory. Depending on the larkspur dose, the intoxication can resurface. Nonetheless, there are risks associated with the use of neostigmine. The use of neostigmine-based treatments may actually aggravate losses in the absence of further treatment because suddenly mobile animals may later develop increased muscular fatigue and dyspnea and may die.

Research results show that low lark­spurs can usually be controlled by applying 2,4-D at the rate of 4 lbs. ae/acre when the vegetative development approaches its maximum but before the first flowers open.

Tall larkspur can be controlled with picloram (1 to 2 lbs. ae/acre) up through the flowering stage. Metsulfuron (1-2 oz. of product/acre) is effective when applied in the early vegetative stage of growth. Plains larkspur can be controlled with picloram (0.25 to 0.5 lb. ae/acre) in the bud stage.

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 toxicity remains high.