Patterson, R.K.,, Extension Assistant Professor, Utah State University
Worwood, D.R., Extension Agent, Utah State University

ABSTRACT

Studies were conducted to determine how herbicide rates and timing of applications influenced the efficacy of herbicides applied to Russian olive (Eleagnus angustifolia) using the frill cut method. Trees were treated in October, 2005 with Roundup (41% glyphosate), Habitat (28.7% imazapyr), or 2,4-D Amine (47.3% dimethylamine salt of 2,4-Dichlorophenoxyacetic acid) at rates of 1.0, 1.5 or 2.0 ml/inch of trunk diameter. All chemicals and rates provided acceptable control of Russian olive, with the 1 ml 2,4-D and the 1.5 ml Roundup treatments showing slightly lower control than other herbicides and rates. This suggests that 1 ml of herbicide/inch of trunk diameter is an acceptable rate using the frill cut method. In a follow-up study, trees were treated with 1 ml/inch of trunk diameter of Roundup or 2,4-D each month from November, 2006 through September, 2007. The results were compared with the 1.0 ml October treatment of the same chemical in the previous study. For 2,4-D, applications in September provided the best control. For Roundup, best control was achieved from applications in January, May, June, July, August and September. This suggests that September is the best time to apply 2,4-D and May through October is the best time to apply Roundup to Russian Olive using the frill cut method.

Introduction

Degradation of riparian areas, pastures and range lands in the Western United States is being intensified by the increasing encroachment of Russian olive (Elaeagnus angustifolia L.). The Russian olive is a small thorny tree or large shrub that is native to Europe. In the early 1900s it was promoted as a conservation plant by soil conservation districts and land grant universities.  Russian olive is an extremely hardy and adaptable plant that tolerates drought, alkaline and saline soils, can fix nitrogen from the air, and reproduces by seed and through root suckers. Trees produce copious small fruits that are relished by many species of wildlife (particularly birds). These attributes make it valuable in windbreak and wildlife plantings but have also allowed Russian olive to spread explosively, out-competing and displacing native vegetation. It often creates a monoculture, reducing vegetative diversity. Although Russian olive fruit is eaten by birds, Muzika and Swearingen (2009) and Stannard, Ogle, Holzworth, Scianna, and Sunleaf, (2002) indicate that solid stands of Russian olive trees support fewer species of birds than native vegetation.  These characteristics, along with its thorny growth habit, have caused many to view Russian olive as an invasive weed.

Russian olive has been declared a noxious weed in several western states and/or counties. Although it is no longer legal to plant Russian olives in these areas, the species continues to spread, reducing the quality of pastures and overpowering native riparian vegetation.  Russian olive is essentially a mono-culture along some sections of riparian areas in western states.  While total eradication of Russian olive is neither likely nor feasible, an aggressive control and maintenance program will help to restore desirable plant diversity.

There are four accepted methods of applying chemicals to Russian olives:

1. Foliar Spray—An herbicide solution is applied directly to the leaves of an actively growing plant. Foliar spraying does not always provide complete control, since leaf pubescence intercepts spray droplets before they reach the leaf surface. Care must be taken to apply herbicide to every branch, as unsprayed branches will not be killed. Dilution of the chemical is usually required.
2. Basal Bark Spray—Herbicide is applied to the lower area of the main trunk(s) of the tree and is absorbed through the bark. The herbicide is usually diluted with an oil or petroleum product, such as diesel fuel, to help with absorption.
3. Frill-cut—A hatchet or ax is used to cut notches through the bark and into the sap wood of the tree. Undiluted herbicide is poured or injected into each notch. Cuts are made with a downward motion so the resultant notches will hold the herbicide. Care must be taken to not girdle the tree with the chop marks.

4. Cut stump—The tree is cut down and the stump is sprayed or painted with herbicide within ten minutes of cutting, paying particular attention to the cambium layer.

An undiluted chemical is more effective with frill cut and cut stump application methods.

There are no effective biological controls available for Russian olive at this time. However, goats have been widely observed eating young growth and even stripping bark off older Russian olive trees.

Russian olives readily propagate sexually and asexually. Seeds are spread far and wide by birds and other wildlife that feed on the fruit. Trees that are cut off or pulled from the ground readily send up root suckers, creating even greater problems. Thus, it is very desirable to kill trees before removing them from the site, or to treat the stumps immediately upon removal of the crown.

Materials and Methods

Chemical Application Methods

For environmental concerns and ease of determining the quantity of chemical applied, the frill-cut method was employed in this field study. Recent field research studies were conducted in Carbon County and Emery County in Utah to help determine application rate and time-of-year effectiveness on frill-cut chemical application control of Russian olive.

Application Rates

Three different rates of Habitat (28.7% imazapyr), 2,4-D Amine (47.3% dimethylamine salt of 2,4-Dichlorophenoxyacetic acid), or Roundup (41% glyphosate) were applied to test trees to determine the efficacy of each herbicide and rate. Undiluted Habitat, 2,4-D and Roundup were applied at the rates of 1 ml, 1.5 ml, and 2 ml per inch of trunk diameter using the frill-cut method of application. One frill cut was made for each inch of trunk diameter and the appropriate amount of chemical (1.0, 1.5, or 2.0 ml) was applied to each cut.

Russian olive has both single-trunk and multiple stemmed growth habits. To reduce the number of variables in this field experiment, single-trunk trees that were six to eight inches in diameter at one foot from ground level were selected for application. Each treatment was applied to three trees, making twenty-seven treatments and three control trees. Control trees received frill cuts like treatment trees did, but no chemical was applied to the cuts. Treatment and control trees were marked with spray paint, and GPS coordinates taken so trees could be identified and evaluated.

 

---