Control and dispersal of Russian olive (Elaeagnus angustifolia L.)

Russian olive (Elaeagnus angustifolia L.) is a noxious, perennial tree or shrub that has invaded thousands of acres across the western United States. Trees are saline tolerant, drought tolerant, form actinorhizal associations with Frankia spp. to fix nitrogen and are actively dispersed by birds. ;Two areas that were researched for this thesis included the control of Russian olive trees through applications of aminocyclopyrachlor and the second being dispersal of Russian olive seeds by European Starlings (Sturnus vulgaris). ;Aminocyclopyrachlor is in a new family of chemistry called the pyrimidine carboxylic acids under the synthetic-auxic herbicides mode of action. We examined several different application techniques (e.g. cut stump, basal bark and hack and squirt applications) to assess the efficacy of aminocyclopyrachlor. The majority of our work consisted of cut stump applications, where we performed two studies evaluating the season of application of aminocyclopyrachlor to Russian olive trees, the effect of size of Russian olive trees on efficacy of aminocyclopyrachlor. Whether cut stump application occurred in summer, fall, or winter, herbicides controlled Russian olive similarly, but not all trees were killed with a single treatment across all timings. Aminocyclopyrachlor at 1 and 2.5% applied in summer controlled 100% of Russian olive. A fall application of 5% aminocyclopyrachlor and a winter application of 30% triclopyr ester similarly killed all trees. Land managers targeting woody species consider 100% control to be acceptable and any regrowth requiring re-treatment is not acceptable. We examined "regrowth factor" as a means to quantify success taking into account the number and height of shoots 1 YAT at one field site. Regrowth was highest in the no herbicide/no oil check population, followed by the 100% Bark Oil Blue LT, 1 and 2.5% aminocyclopyrachlor in fall and 5% aminocyclopyrachlor in both fall and winter. No regrowth was recorded for the triclopyr ester for all three application timings as well as the summer and winter applications of 1 and 2.5% aminocyclopyrachlor, and the fall application of 5% aminocyclopyrachlor. Tree size is an important factor influencing efficacy and the interaction between treatment and site was significant where herbicides were more effective on smaller trees. For 3 to 9 inch trees, herbicide treatments controlled Russian olive similarly (88-100% control) and more effectively than the 100% JLB oil PLUS (50%) and the no herbicide/no oil check trees (47%). No herbicide treatment killed all 9 to15 inch Russian olive trees 1 year after treatment (1YAT), but 1% and 2.5% aminocyclopyrachlor with JLB oil PLUS, 30% triclopyr ester with JLB and 2.5% aminocyclopyrachlor with Bark Oil Blue LT controlled 88 to 93% of trees in this size class. Regrowth from larger trees was observed to be highly variable within treatments. ;aWe also examined the efficacy of aminocyclopyrachlor for the hack and squirt methodology as a means to control Russian olive trees. We compared hack and squirt applications of aminocyclopyrachlor to imazapyr (Habitat), glyphosate (Rodeo), aminopyralid (Milestone), triclopyr amine (Garlon 3A), Milestone VM+ (10:1 triclopyr amine + aminopyralid), and a 50:50 aminocyclopyrachlor + triclopyr amine mixture. Trees were 'hacked' using a hand held ax for every 3 inches of trunk diameter and then injected with 1 ml of undiluted herbicides. We found that aminocyclopyrachlor controlled 91% of Russian olive trees 1YAT. This level of control was comparable to both industry standards, glyphosate and imazapyr (94% and 98%, respectively). A 50:50 mixture of aminocyclopyrachlor and triclopyr amine controlled 98% of Russian olive trees 1YAT. Products containing aminopyralid (e.g. Milestone and Milestone VM+) had lower mean control (84% and 89%, respectively), than aminocyclopyrachlor. Triclopyr amine had the lowest percent control when applied alone at both field sites (77%). From our studies we showed that aminocyclopyrachlor is comparable to industry herbicide standards and thus, is an effective tool to control Russian olive trees by cut stump and hack and squirt applications. ;Previous research identified 51different species of birds that fed on and likely dispersed Russian olive seeds. European Starlings are invasive birds that were introduced into North America in the 1890s. We used field photographic observations and a controlled feeding study to gain a better understanding of the role European Starlings play in dispersal of Russian olive seeds. Our data indicate that indeed this bird species is a potential dispersal of Russian olive. Two studies were conducted to examine the dispersal of Russian olive seeds by European Starlings. In the first study, Russian olive trees were monitored for 1 year at two field sites to determine feeding behaviors of wild animals on Russian olive seeds using two trail cameras (WSCA01 Wing-Scapes Birdcam and a Moultrie MFH-DGS-I60 Game Spy digital camera). In the second study, 20 European Starlings were collected in the field and housed at the USDA-NWRC research facility in Ft. Collins, CO. Birds were kept in individual cages during the experiments where they were fed 25 Russian olive seeds per day and monitored for behavior using a 17 hour camcorder. Germination and viability of ingested seeds were compared to control seeds, hulled seeds, seeds ground on sandpaper and nicked, and seeds soaked in 17.8 M sulfuric acid (H2SO4) for 1hour. In the observational study, we determined that European Starlings did feed on Russian olive seeds in the wild, particularly in the late fall and early winter months (November to December). We also learned from the controlled experiment that European Starlings redily consume Russian olive seeds, with the majority of seeds being regurgitated after a 30 minutes of digestion. Digested seeds had the highest level of germination (57%) compared to hulled seeds (40%) and ground/nicked seeds (30%). Viability tests confirmed that digested/regurgitated seeds remained viable (87%) and had no net loss in viability after consumption.