Cooperation Manages Exotic Plant Threat to the Ecosystem in Butte and Custer Counties
The Situation
Introduced into North America from Eurasia, leafy spurge (Euphorbia esula) is an aggressive, long-lived, deep-rooted, herbicide resistant perennial invader.
This exotic plant spreads vegetatively up to 15 feet per year and produces an abundance of sticky seeds, explosively propelled up to 15 feet.
Introduced without its predators or parasites, leafy spurge forms dense stands that exclude other vegetation. Its bitter irritating sap discourages grazing on or near it by virtually all wildlife and domestic livestock.
Spurge successfully colonizes a wide range of habitats from dry rocky slopes to moist riparian areas.
These characteristics make leafy spurge a threat to the ecology of intermountain rangelands and domestic forage production of the area.
In Butte and Custer Counties
Introduced in Butte and Custer counties in the early part of the century as an ornamental, an appreciation of the invasive nature of the plant did not develop locally until the 1950s.
Leafy spurge now infests more than 8,000 acres of public and private lands in Butte and south Custer Counties. This includes remote mountainous areas, farm fields, roadsides, the banks of irrigation canals and natural waterways of the area.
Spurge spreads in flowing water, on farm machinery, in harvested forage, and on the coats of wild and domestic animals. Spurge is a favored food of mourning doves, which transport the seed long distances in unpredictable directions.
In the past, private individuals and public land managers have been unable or reluctant to restrict the expansion of spurge or attempt eradication due to costs that often exceeded the value of the land.
Our Response
Working with public and private land managers in the area, we assembled an informal area-wide plan to reduce the spread of leafy spurge and establish biological control agents inside the infested area.
Education and Information
Public education efforts include posters, trail head displays, newspaper articles and weed identification clinics.
Various agencies, sharing information and equipment, use conventional and GPS/GIS techniques for mapping and inventorying spurge.
Extension and county weed departments conduct landowner education to raise awareness and obtain compliance with state law. Herbicide demonstrations by extension and aggressive efforts by county weed departments and irrigation districts demonstrate that the rate of spread of spurge can be significantly and economically reduced.
Biological Control
Biological control efforts are underway to establish and redistribute insects known to be effective against leafy spurge.
APHIS (Animal Plant Health Inspection Service) released Aphthona nigriscutis (flea beetle) in a remote location in south Custer County in 1988. The larva of this and related organisms feed only on the roots and shoots of leafy spurge. Adults feed on the leaves. In cooperation with the USFS (US Forest Service), BLM (Bureau of Land Management) and county weed departments, we have harvested and re-released thousands of A. nigriscutis.
Using grant funds provided by the Idaho Department of Agriculture, we are currently purchasing and releasing other species in an effort to establish harvestable populations for redistribution.
Certification
Finally, county weed departments in these counties participate in the Idaho weed-free hay certification program.
Achievements
Leafy spurge is no longer expanding in the area as rapidly as before.
Landowners and public land managers recognize the threat to the community from this plant and cooperate in implementing control measures. Herbicide demonstrations prove to most that living with leafy spurge is economically possible.
Successful demonstration of biological control provides expectation for long-term non-chemical management. Establishment of new insectaries of additional species of biocontrol agents continues. We have successfully begun implementation of biological control by establishing A. nigriscutis in at least six new locations in three years, and we suspect others.
Cooperators
- Butte County Department of Noxious Weeds
- Custer County Department of Noxious Weeds
- Salmon District, Bureau of Land Management (BLM)
- Big Butte Resource Area, Idaho Falls District, Bureau of Land Management (BLM)
- Weed Coordinator, Idaho Department of Agriculture
- Idaho Department of Transportation
- Big Lost Irrigation District
- Butte County Commissioners
- Custer County Commissioners
- US Animal Plant Health Inspection Service (APHIS)
- Lost River District, Salmon-Challis National Forest (USFS)
- Butte and Custer County Landowners
The Future
We intend to continue the program of cooperation between agencies for public education on, and suppression of leafy spurge. We are optimistic that the informal program can be formalized into a basin-wide management plan that will provide continuity when personnel move.
Releases and harvesting of biological control agents will continue within the infested area. Herbicides will continue to suppress the spread of this plant on the perimeter of the infestation.