Why Larkspur is Dangerous for Cattle and How to Manage It
As a result of this year’s wet weather in areas of Nebraska, ranchers and land managers can expect some changes in weed species abundance in range and pastures. Larkspur is one weed that’s showing up and causing some problems. At the Panhandle Research, Extension and Education Center in Scottsbluff we have had more phone calls and in-person visits from ranchers regarding larkspur management in the last month than we have in the previous five years combined.
Several species of larkspur (Delphinium spp) are native to Nebraska and can be poisonous to cattle and other livestock.
Prairie larkspur (Delphinium virescens Nutt.) is the most common across the state and has white or pale blue flowers.
Geyer larkspur (Delphinium geyeri Greene) and twolobe larkspur (Delphinium nuttallianum Pritz.) grow in the panhandle and have light blue or violet flowers.
How does larkspur affect cattle?
Larkspurs contain highly toxic norditerpenoid alkaloids that are quickly lethal to cattle with consumption of as little as 0.5% of body weight. Larkspurs are the most palatable to cattle and when cattle are at the highest risk of poisoning in late April through June. Cattle are less susceptible to poisoning after seeds have dropped later in the growing season. Sheep tend to be less susceptible to poisoning throughout the growing season.
How to manage or control larkspur
Managing the timing of cattle grazing may be the most viable option for pastures with larkspur, but there are some herbicide options for larkspur control. Two active ingredients are labeled for control of larkspur, picloram and metsulfuron-methly. Picloram is sold under the tradename Tordon® 22K and metsulfuron-methyl as Escort® XP. There are also a number of other labeled herbicides which contain either picloram or metsulfuron-methyl in a mix with other active ingredients (Table 1). Picloram containing herbicides are labeled for geyer, prairie, and tall (Delphinium exaltatum) larkspur while metsulfuron-methyl containing products are labeled for dunecap (Delphinium occidentale) and tall larkspur. Given that there are dozens of native larkspur species across the country, both active ingredients likely control more than the species listed, but have been tested only on those species. Products containing picloram are restricted-use pesticides that require the applicator to have a pesticide applicator license, due to the risk of groundwater contamination and surface water runoff.
The timing of herbicide applications depends on the herbicide used, herbicide rate, and species targeted. Larkspur can be controlled in the vegetative phase of growth, the budding stage, or in the flowering stage, and the herbicide label should be consulted while planning an herbicide application. In 1992, picloram was able to control larkspur species at 2 and 4 pints an acre across all plant growth stages, while metsulfuron-methyl was most effective when applied in the vegetative stage. Herbicide use should be limited in areas where non-target native forbs and flowering species might be negatively affected.
Ralphs, MH, JO Evans, SA Dewey (1992) Timing of Herbicide Applications for Control of Larkspurs (Delphinium spp.). Weed Science 40:264–269
Stubbendieck, J., M. P. Carlson, C. D. Dunn. 2018. Nebraska plants toxic to livestock. UNL Extension Circular 3037. 196 p.
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