By Celestine Duncan, Vanelle Peterson, Jim Ghekiere and Stan Hutala
Techline editor/field scientist, Dow AgroSciences, and Liberty County Weed District respectively.
Russian olive (Elaeagnus angustifolia) is an invasive tree of Eurasian origin that was introduced as an ornamental plant to North America. Although considered a desirable component of windbreaks in some semi-arid environments in the West, it has spread from intentional plantings and invaded many riparian areas. Once naturalized, the plant can dominate riparian and lowland sites, causing serious ecological changes to these important habitats. Potential losses include wildlife, agriculture, and recreation.
Historical management of Russian olive includes mechanical cutting, mowing or shredding followed by herbicide treatments. However, there was limited data on the effectiveness of aerial application of triclopyr ester (Remedy® Ultra) or amine (Garlon® 3A*) applied alone and in combination with Milestone® specialty herbicide on Russian olive. Research methods and results from a study conducted in northcentral Montana are described within this article.
The objective of the study was to compare the effectiveness of aerial treatment of Remedy Ultra applied alone, to Remedy Ultra or Garlon 3A applied in combination with Milestone specialty herbicide to Russian olive. The study site is located on the Marias River floodplain in northcentral Montana just downstream from a cooperative Russian olive removal project by Liberty County Weed District and the Bureau of Land Management. Russian olive trees in the study area ranged in size from seedlings less than 1 foot in height, to 20 foot tall trees. Cooperators in the study included Liberty County Weed District, landowner Jody Hansen, and Dow AgroSciences LLC.
Plot size for each herbicide treatment was about seven acres. Prior to application, two-100 foot permanent transects were located in each treatment area and a non-treated control. Transect sites were selected to include a mix of small and large Russian olive trees. Trees size and location were recorded within 12 feet on either side of the center of the transect (2400 sq ft). Herbicide treatments were applied with a Hiler helicopter at 3 gallons total solution per acre on August 26, 2016 (Table 1). Growing conditions were good to excellent at application and environmental conditions were favorable for aerial treatment.
The percent defoliation of Russian olive trees was recorded within each transect 10 months after treatment (MAT) and the number of live and dead trees (complete defoliation/no regrowth) recorded 12 MAT. Additional observations were collected 12 MAT on Russian olive trees growing outside of transects to increase the number of observations.
Herbicide, application rate*^, and number of trees by size category observed in each area 12 months after treatment.
Results of the study showed that the height of Russian olive trees at time of treatment was an important factor influencing the degree of defoliation and control. Herbicide treatments applied to trees less than 6 feet in height provided greater defoliation at 10 MAT than the same treatments applied to larger trees (Figure 1). Remedy® Ultra alone at 2 quarts per acre (qts/A) provided 54% defoliation to trees less than 6 feet tall at 10 MAT; however, the addition of Milestone® at 7 fluid ounces per acre (fl oz/A) to either Remedy Ultra or Garlon® 3A increased the level of defoliation to 97 and 92% respectively for trees in this size category. As tree size increased, the percent defoliation on Russian olive trees declined to less than 50% for trees greater than 10 feet tall regardless of herbicide treatment. Field observations suggest that Russian olive density also influenced the level of defoliation and control. As tree density increased the percent defoliation declined, possibly as the result of poor herbicide coverage with aerial application under dense tree canopy.
Percent defoliation of various size Russian olive trees 10 months following aerial application of Remedy® Ultra or Garlon® 3A plus Milestone® specialty herbicide compared to Remedy Ultra alone.
At 12 MAT, complete control (no regrowth) of Russian olive trees was greatest on trees 6 feet or less in height, and with treatments that included Milestone (Figure 2). There was no difference in Russian olive control between Garlon 3A plus Milestone and Remedy Ultra plus Milestone 12 MAT. Russian olive trees that were not completely defoliated at 10 MAT continued to regrow by 12 MAT. There were no Russian olive seedlings observed in herbicide treatments that included Milestone (Figure 3). Russian knapweed and Canada thistle growing in association with the trees were also controlled with Milestone.
Percent control (no regrowth) of Russian olive trees less than and greater than 6 feet in height 12 months following aerial application of Remedy® Ultra or Garlon® 3A plus Milestone® specialty herbicide compared to Remedy Ultra alone.
Percent control of Russian olive seedlings 12 months following aerial application of Remedy® Ultra or Garlon® 3A plus Milestone® specialty herbicide compared to Remedy Ultra alone.
Russian olive infestations often include a mix of trees ranging in size from seedlings less than 1 foot tall to mature trees more than 20 feet in height. Aerial applications of Remedy® Ultra or Garlon® 3A in combination with Milestone® at 7 fl oz/A will effectively control Russian olive trees 6 feet or less in height (Figures 5 and 6). Aerial application will reduce the amount of time and labor involved in controlling Russian olive infestations especially those that are newly invading. Larger trees (greater than 6 feet tall) should be removed by basal bark treatments, or by cutting, mowing or shredding, followed by cut surface herbicide treatments prior to aerial application (http://techlinenews.com/articles/2012/12/30/saltcedar-and-russian-olive-management). This will control large trees and open the canopy for more effective herbicide coverage of smaller Russian olive trees and seedlings during aerial application. The addition of Milestone has the benefit of controlling Russian olive seedlings for at least one year following treatment, and removal of invasive broadleaf plants such as thistles and knapweeds that may be present on the site.
Non-target desirable woody vegetation such as buffalo berry (Shepherdia canadensis), rubber rabbitbrush (Ericameria nauseosa) and cottonwood (Populus sp.) may be damaged during aerial application of either Remedy® Ultra or Garlon® 3A in combination with Milestone®. If damage to desirable shrubs cannot be tolerated, then Russian olive growing near desirable woody plants can be removed with basal bark or cut surface herbicide applications, and buffers established to minimize exposure during aerial application. Although injury to buffalo berry and rubber rabbitbrush was evident within the study area, young willows (Salix sp) were observed growing in all three of the herbicide treated sites 12 MAT (Figure 4).
Figure 4. Willows were released in some areas following removal of Russian olive with Remedy® Ultra or Garlon® 3A plus Milestone® specialty herbicide, or Remedy Ultra alone.
Recommendations for aerial herbicide application on Russian olive:
- Remove trees larger than 6 feet in height prior to aerial application. This can be accomplished by cutting followed by cut surface herbicide treatments or by basal bark herbicide treatments. http://techlinenews.com/articles/2012/12/30/saltcedar-and-russian-olive-management
- Remove trees immediately adjacent to water or other areas that may be difficult to treat by aerial application.
- Identify areas of non-target desirable woody vegetation. If damage cannot be tolerated, Russian olive near these plants can be removed by cutting followed by cut surface herbicide treatments or by basal bark herbicide treatments.
- The addition of Milestone® at 7 fl oz/A to either Garlon® 3A or Remedy® Ultra is critical to increase Russian olive control and aid in controlling new Russian olive seedlings.
- Follow-up management for at least two years after aerial application is needed to control Russian olive regrowth and seedlings that may germinate the second growing season.
Figure 5. Control of Russian olive trees less than 6 feet in height was greatest with Milestone® specialty herbicide at 7 fl oz/A plus either Garlon® 3A at 2.8 qts/A (left) or Remedy® Ultra at 2 qts/A (middle) compared to Remedy Ultra alone at 2 qts/A (right) 12 months after treatment.
Figure 6. Control of Russian olive trees greater than 6 feet in height ranged from 100% (left) to less than 30% defoliation (right) with Garlon® 3A at 2.8 qts/A plus with Milestone® specialty herbicide at 7 fl oz/A. Results were similar with Remedy® Ultra plus Milestone.
*VASTLAN SPECIALTY HERBICIDE IS FORMULATED AS A SOLUBLE LIQUID AND CONTAINS 4 POUNDS ACID EQUIVALENT PER GALLON OF TRICLOPYR CHOLINE. THE CHOLINE FORMULATION OF TRICLOPYR REDUCED THE SIGNAL FROM “DANGER” ON GARLON 3A TO “WARNING”. GARLON 3A HAS A 3 LB ACID EQUIVALENT PER GALLON.
™ ®Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. Milestone is not registered for sale or use in all states. Contact your state pesticide regulatory agency to determine if a product is registered for sale or use in your state. Label precautions apply to forage treated with Milestone and to manure from animals that have consumed treated forage within the last three days. Consult the label for full details.
State restrictions on the sale and use of Remedy Ultra apply. Consult the label before purchase or use for full details.
Always read and follow label directions.
Active ingredients for products mentioned in this article. Product (active ingredient): Milestone (aminopyralid); Garlon 3A (triclopyr-amine); Remedy Ultra (triclopyr-ester).