RBC I Leafy spurge (Euphorbia esula L.) is an aggressive invasive weed responsible for considerable impacts on native and agricultural plant communities. This rhizomatous perennial is found in Rio Blanco and Moffat county pastures, rangeland, cropland, roadsides, shelter-belts and other non-cultivated sites, including riparian habitats up to water’s edge.
The plant is native to Europe and Asia, but seldom creates infestations of significant economic importance. It was first identified in North America in Massachusetts in 1827, North Dakota in 1909 and in most other Western states, including Colorado, and the Prairie Provinces in the following years. Direct control costs in the U.S. are estimated to be in excess of $150 million annually. Degradation of rangelands and wildlife habitat make the total economic impact of this weed very significant in North America.
Leafy spurge is long-lived with an extensive system of tough woody roots and rhizomes in the top two feet of soil. The roots and rhizomes produce vegetative buds that can develop stem shoots that can surface from a depth of three feet.
Rhizomes can grow laterally 30 feet a year and roots have been found as deep as 30 feet. This robust biology requires a herbicide that can control shoot buds as deep as three feet. Numerous short roots are important for the uptake of water and nutrients
The yellow-green flowers, born in umbels on 1½ to 3 foot stems, are preceded by a false flowering a couple of weeks earlier as the bracts turn yellow. Early season herbicide control of leafy spurge should take place before the nectar is released to avoid impacting pollinators. The seeds can be spread up to 15 feet when the ripe seed capsules burst.
Control of leafy spurge is not easy, but is more readily accomplished on uplands than on riparian sites. Both herbicide use and biological controls have been successfully used to control leafy spurge, but the particular circumstances in the riparian zone make both methods problematic.
Early season application of picloram has been the standard herbicide treatment for leafy spurge control.
Imazapic applied with a methylated seed oil is very effective for fall application and is safe to use around some trees, though grass injury is likely. Quinclorac applied in the fall for two years can provide 90 percent spurge control, but also may injure grasses. Each of these herbicides are restricted over high water tables and permeable soil. Always read and follow the label before purchasing or using any pesticide.
Targeted grazing and insects can be effective bio-controls, and more so when used together. Managed grazing of leafy spurge with sheep or goats over at least four to five years can be very effective. Several species of Apthona flea beetles feed on leafy spurge and over time reduce plant vigor and seed production.
Unfortunately, experience has shown that mosquitoes can drive sheep or goats and their herders out of riparian sites and seasonal high water can inundate overwintering flea beetles.
Devising an effective strategy for the control of leafy spurge along the rivers of northwest Colorado presents a set of challenges to overcome.
Greg Brown is the Routt County Weed Supervisor and is spearheading a coordinated effort to control the spread of leafy spurge in Northwest Colorado.