Big Horn County is located in north central Wyoming. Russian olive, Elaeagnus angustifolia, was listed as a state noxious weed in 2007. Russian olive removal projects were initiated across the state. A standard treatment program involves the mechanical removal of all above ground growth followed by a foliar treatment to regrowth. Standard herbicide recommendations for treating the regrowth proved to be inadequate. The objective of this project was to identify an effective herbicide, rate and timing. Russian olive trees were mechanically removed in February 2008 using a mulcher mounted on a skid steer. Plots were set up as a randomized complete block with three repetitions. Treatments included two timings: 5 months (July 2008) after removal when regrowth was 2-4 feet tall and 8 months (October 2008) after removal to regrowth from 3-8 feet. Early timing treatments were triclopyr ester alone at 2, 3, and 4 lb ae/A (2, 3, and 4 qts/A Remedy® Ultra/Garlon® 4 Ultra), triclopyr ester plus aminopyralid (Milestone®) at 2+ 0.11 lb ae/A (2 qt + 7 fl oz/A). Later timing treatments were triclopyr ester alone at 2 and 3 lb ae/A, triclopyr ester plus 2,4-D at 1 +1 lb ae/A, triclopyr ester plus aminopyralid at 2+0.11 lb ae/A, aminopyralid+metsulfuron at 0.11+.02 lb ae/A (Chaparral® at 3.3 oz/A), and triclopyr amine at 3 lb ae/A (Garlon® 3A^ at 4 qts/A [Vastlan™ specialty herbicide at 3 qts/A]) plus aminopyralid at 0.11 lb ae/A. All treatments included 1 qt of MSO/A. Plots were visually evaluated for percent control 1 YAT in October 2009. None of the early treatment plots yielded acceptable levels of control. In the later application timings, triclopyr ester at 2 lb ae/A plus aminopyralid at 0.11 lb ae/A yielded the highest control at 97%. Triclopyr ester at 3 and 4 lb ae/A both showed 93% control. Triclopyr ester at 2 lb ae/A provided only 66% control. The treatment that provided the lowest level of control at 47% was the triclopyr ester tank mixed with aminopyralid+metsulfuron at 1 lb+.11+.02 lb ae/A. Applications in July will not provide effective control of Russian olive regrowth. Treatments applied in October when there was more regrowth were significantly more effective. Adding 0.11 lb ae/A (7 fl oz/A) of aminopyralid to 2 lb ae/A (2 qt/A) triclopyr ester improved Russian olive control to 95% from 66% when triclopyr ester was applied at 2 lb ae/A alone.

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^Application rate conversion for Garlon 3A® to Vastlan™ specialty herbicide

Citation: RUSSIAN OLIVE CONTROL IN BIG HORN COUNTY, WYOMING. Ruth Richards*, Big Horn County Weed and Pest Control District, Greybull, WY; Mary B. Halstvedt, Dow AgroSciences, Billings,MT and Tom D. Whitson, University of Wyoming, Professor Emeritus.