Invasive Watch: Autumn and Russian olive (elaeagnus umbellate and e. angustifolia, respectively)
WHAT TO LOOK FOR.
Autumn olive and Russian olive are non-native rapidly growing deciduous bushy shrubs or small trees, often reaching heights of 20 and 35 feet. Both produce abundant fruits, which are widely dispersed by birds and animals, resulting in many scattered plants.
Leslie J. Mehrhoff, University of Connecticut
Autumn olive’s leaves are alternate, generally oval, dark green to gray-green above and silvery beneath. Small silvery-white to yellow flowers appear after the first leaves, producing many small red berries in the fall. The bark is usually brown to yellowish-brown and smooth except old stems become fissured, exposing light-brown inner bark.
Patrick Breen, Oregon State University
Russian olive leaves are narrower, longer and dark green with silver scales on the underside. It produces yellow flowers and dry yellow fruit in the fall. The bark is smooth, reddish brown, and the twigs are typically covered with thorns.
WHERE THEY ARE FOUND.
Autumn olive is native to eastern Asia, while Russian olive is a native of Asia and southern Europe. Since the 1800s, both have been used in North America as ornamentals in landscaping, for strip mine reclamation and erosion control.
They are also frequently introduced to provide wildlife habitat. However, even with the food and cover these trees provide, it’s been determined that native species provide more benefits without destroying native biodiversity. Russian olive, especially, will monopolize water supplies in wet or flooded soils, making these sites unfavorable for native tree species.
The most common sites include open woods, forest edges, roadsides, fencerows, old fields, pastures and heavily disturbed areas. Once established, they tend to form dense thickets, which are then potential fuel loads for wildfires. They are challenging and expensive to eradicate and can interfere with tree regeneration.
HOW TO TREAT THEM.
Apply 20 percent to 30 percent of Garlon® 4 Ultra specialty herbicide in basal oil or Pathfinder® II specialty herbicide (which is a convenient ready-to-use product) as basal bark or cut-stump treatments. These treatments can be made anytime of the year, including the dormant season, allowing for work to be spread out.
Another option is a foliar treatment of 7 fluid ounces of Milestone® specialty herbicide plus 3 quarts of Garlon 4 Ultra specialty herbicide per acre. Apply to undisturbed plants — or, if mowed or cut, wait until the resprouts are at least 3 to 4 feet tall (usually 1 growing season). It is very important for the applicator to obtain good foliar coverage with the herbicide spray solution.
Elimination of these plants requires follow-up treatments for two or more years. Establishing a thick cover of desirable trees and/or grasses will discourage seedling emergence and establishment, making the selectivity of both Milestone and Garlon 4 Ultra valuable as they allow for release of most grass species.