Herbicide Application Timing is Key to Controlling Russian Olive Regrowth

Photo by Norbert Frank, University of West Hungary, bugwood.org

Photo by Norbert Frank, University of West Hungary, bugwood.org

Russian olive (Elaeagnus angustifolia) is a Eurasian tree originally introduced to North America as an ornamental plant. The tree is considered a desirable component of planted windbreaks in some semi-arid environments in the West. Since its introduction, Russian olive has spread from intentional plantings and invaded many riparian areas where it dominates the plant community causing serious ecological changes. Potential losses include wildlife, agriculture, and recreation.

Managing Russian olive trees includes mechanical cutting, mowing or shredding followed by herbicide treatments. Cut stump or modified cut stump herbicide applications with Vastlan™ specialty herbicide applied immediately following mechanical removal, or with Garlon 4 Ultra applied prior to re-sprouting will control Russian olive (See Saltcedar and Russian Olive Management). However, if herbicide treatments are not applied during this timing window, Russian olive will regrow quickly from non-treated stumps.

Research conducted in Wyoming and Nebraska studied the effectiveness of various herbicides and application timing on Russian olive regrowth following mechanical removal. Objectives of the studies were to:

  1. Identify an effective treatment for controlling Russian olive regrowth;
  2. Determine the best timing for herbicide treatments; and
  3. Identify the most cost- effective treatment (Wyoming location).

This article describes the results from these studies.

 

Material and Methods

Big Horn County, Wyoming

(Abstract: http://techlinenews.com/articles/2014/ro-richards-wsws-2010)

  • Russian olive trees were mechanically removed in February 2008 using a mulcher mounted on a skid steer (Figure 1).
  • Herbicide treatments were applied to Russian olive regrowth either in July or October 2008 (Table 1).
  • Height of Russian olive regrowth was 2 to 4 feet in July and 3 to 8 feet in October.
  • Treatments were applied in a randomized complete block design with three replications.
  • Plots were visually evaluated for percent control in June and October 2009.  

Henry, Nebraska

(Abstract: http://techlinenews.com/articles/2014/scro-sleugh-wsws-2010)

  • Russian olive trees were clipped to ground level in the spring 2008 to simulate a mechanical cutting operation and allowed to regrow through summer months.
  • Herbicide treatments were applied over the top of regrowth in September 2008 (Figure 2).
  • Treatment plots were arranged as a randomized complete block design with three replications.
  • Plots were visually evaluated for percent control nine months following treatment (June 2009).
Figure 1. Mulcher removing top growth of Russian olive trees in Wyoming.

Figure 1. Mulcher removing top growth of Russian olive trees in Wyoming.

Figure 2. Russian olive regrowth at time of application (September 2008) in Henry, Nebraska.

Figure 2. Russian olive regrowth at time of application (September 2008) in Henry, Nebraska.

Table 1. Herbicide, application rate, and date of application to Russian olive regrowth following mechanical removal in Big Horn County, Wyoming and Henry, Nebraska.

Table 1. Herbicide, application rate, and date of application to Russian olive regrowth following mechanical removal in Big Horn County, Wyoming and Henry, Nebraska.

 

Results

Results of the studies show that height of Russian olive regrowth at time of treatment is an important factor influencing control.

In Wyoming, herbicides applied in July to 2 to 4 foot regrowth provided significantly less control than similar treatments applied in October to 3 to 8 foot regrowth (Figure 3). Garlon 4 Ultra at 3 and 4 quarts per acre (qt/A) and Garlon 4 Ultra at 2 qt/A plus Milestone® at 7 fluid ounces per acre (fl oz/A) applied in fall provided more than 90 percent control of Russian olive regrowth one year after treatment (1 YAT). The addition of Milestone at 7 fl oz/A to Garlon 4 Ultra at 2 qt/A provided significantly greater Russian olive control (97%) compared to Garlon 4 Ultra at 2 qt/A alone (66%). Based on conclusions from the Wyoming study, the most cost effective and efficacious treatment was Garlon 4 Ultra at 2 qt/A plus Milestone at 7 fl oz/A applied in fall.

Figure 3. Percent control of Russian olive treated with Garlon 4 Ultra alone or with Milestone in Wyoming one year after treatment.

Results were similar in Nebraska nine months following treatment. Garlon 4 Ultra (3 qt/A) plus Milestone (7 fl oz/A) provided 98 percent control compared to the same rate of Garlon 4 Ultra alone at 50 percent control. Russian olive control with Garlon 4 Ultra plus Milestone herbicide provided similar Russian olive control as imazapyr (Nebraska location) nine months after treatment. However, grass injury ranged from 50 to 85 percent with imazapyr treatments compared to 0 to 5 percent grass injury with Garlon 4 Ultra plus Milestone (Figure 4 and 5).

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Figure 4. Desirable grass injury ranged from 50 to 85 percent with imazapyr treatments (left) compared to 0 to 5 percent grass injury with Garlon® 4 Ultra plus Milestone® (right) in Nebraska nine months after treatment.

Figure 5. Biennial thistles and other weedy species established in imazapyr-treated plots the year after treatment in Nebraska.

Figure 5. Biennial thistles and other weedy species established in imazapyr-treated plots the year after treatment in Nebraska.

 

Management Implications

Russian olive will re-sprout following cutting, mowing or shredding operations if herbicides are not applied to the cut surface or stump. Results of these studies indicate that:

  • Herbicide treatments to Russian olive regrowth must be delayed until regrowth is at least 3 to 4 feet in height (six months or more following cutting/mowing) to achieve acceptable control. This allows time for plants to develop adequate leaf area for more herbicide uptake from a foliar application. It may be necessary to delay the application until the year after cutting, or at least until late summer or fall following a cutting/mowing event the previous winter or spring.
  • The addition of Milestone herbicide at 7 fl oz/A to Garlon 4 Ultra at 2 qt/A increased Russian olive control and was the most cost effective treatment. The addition of Milestone also provides excellent control of invasive broadleaf plants such as perennial and biennial thistles present on the treated site without significant injury to desirable grasses.

 

References

 


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.

®™Trademark of The Dow Chemical Company (“Dow”) or an affiliated company of Dow. State restrictions on the sale and use of Garlon 4 Ultra apply. Consult the label before purchase or use for full details. Milestone and Vastlan are 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. Always read and follow label directions.