Pest Watch 25


Russian olive (Elaeagnus angustifolia) thorny olive (E. pungens) autumn olive (E umbellata)

These Eurasian shrubs have been promoted as ornamentals and wildlife food and hailed as excellent choices for shelter belts, highway right-of-ways, and strip-mine reclamation. The former U. S. Soil Conservation Service (now the Natural Resources Conservation Service) widely promoted the autumn olive cultivar ‘Cardinal’ wherever soil stabilization was desired. Although they are not legumes, elaeagnus species are capable of fixing nitrogen, which allows them to thrive on poor, infertile sites. In addition, autumn olive fruits have recently been shown to possess a particularly high lycopene content-17 times that of fresh tomatoes.

Nevertheless, many people now consider all three shrubs villains. Their wide adaptability, combined with birds’ dispersal of the fruits, has caused these species to become invasive weeds. Russian olive is a particular problem in the central and western plains, while autumn olive and thorny olive have become similarly established in the Northeast Midwest and Southeast.

BIOLOGY: These spiny shrubs or small trees reach a height of 20 feet and can create impenetrable thorny thickets. Russian olive has green to silver-gray leaves; thorny olive and autumn olive have grayish green leaves. All three have a characteristic silvery white backing to the undersides of their leaves.

Russian olive and autumn olive bloom in the spring after their leaves have emerged. They bear clusters of silvery white to yellow fragrant tubular flowers in the axils of their branches. Small oval fruits mature in late summer and early fall. Russian olive fruit are hard and light green to yellowish red in color; autumn olive produces juicy red fruit.

The evergreen thorny olive produces clusters of silvery white to brown fragrant flowers in the fall. White fruits ripen to red the following spring. A single thorny olive shrub can produce 200,000 seeds.

CONTROL: Small seedlings can be hand pulled. The entire root should be removed to prevent resprouting. Specimens up to several inches in diameter may be removed with a weed-pulling tool. This is easiest when the ground is moist. Older plants that have been cut to the ground will resprout from the stump. In big areas, bulldozers provide the best method of removal.

For the homeowner, herbicide applications are the easiest ways to eliminate mature elaeagnus. In basal-bark applications a herbicide containing triclopyr (Bayer Advanced Brush Killer Plus, Ortho Brush-B-Gon) is sprayed onto the trunk from ground level up to two feet, around the entire circumference. In the cut-stump approach, the plant is cut back at or close to ground level and glyphosate (Roundup Poison Ivy and Tough Brush Killer Plus] or triclopyr is applied to the fresh wound. Both glyphosate and triclopyr can also be applied to the foliage. Any of the above treatments should be carried out after new leaves have fully expanded and when the plants are actively growing. In western states these herbicides are best used in the spring, because late summer drought reduces their effectiveness.

A Gardening Life

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