Performing Department
Cooperative Extension Service
Non Technical Summary
Invasive species are considered a leading cause for the loss of biodiversity and natural resources prompting many land and resource managers to initiate control programs. Prunus padus an invasive tree in the boreal forests of Alaska is believed to alter fish and wildlife habitat. Herbicides are often used to control Prunus padus because roots or stumps left after removal of the above ground plant will regenerate. Herbicides though have unintended impacts to natural resources and non-target vegetation due to movement through drift or runoff and persistence beyond the time needed for control. To avoid these non-target impacts invasive plant managers utilize direct treatments such as basal bark (application of herbicide to trunk of tree from ground up to 36 cm) treatments of trees. Previous work has indicated that these basal bark applications to Prunus padus do release herbicide to the soil resulting in non-target impacts and potential accumulation of aminopyralid, a persistent herbicide. However this prior work did not study the complete removal of Prunus padus trees from an infestation and if removal of denser infestations results in an increase in frequency of non-target impacts that deserve caution. This study will determine how the density of trees treated in a plot impacts the frequency of observed non-target impacts and accumulation of herbicide in the soil. Results of this work will inform managers of thresholds of Prunus padus infestation that basal bark treatments should not exceed. Further this research is an example of issues to study to avoid non-target impacts with similar infestations where direct treatments are used.Invasive species concerns have further prompted land managers to require the use of certified weed free straw and forage that is used for bedding, feed, and production of erosion control materials. Producers in Alaska have embraced this value-added product providing it to the Iditarod sled dog races, general consumers, and manufacturers of erosion control tubes. Production to meet demand is hampered though by broadleaf weed species that can set seed multiple times in a growing season. The use of persistent herbicides would control these weed species, however, in some instances carry over has caused damage to rotational crop species leading producers to stop use of these herbicides. Without the use of persistent herbicides large portions of fields are not able to pass certification limiting the availability of weed free straw in Alaska. This project will trial new rotational strategies and determine if carry over from fallow year applications provides the desired weed control without impacting species used in crop rotations specifically peas and potatoes.Of paramount importance to developing an understanding of herbicide persistence is the sorption characteristics of herbicides under various soil and climatic conditions that occur at northern latitudes. Aminopyralid and clopyralid are popular herbicide in Alaska because they provide effective control of orange hawkweed (Hieracium aurantiacum), bird cherry (Prunus padus), bird vetch (Vicia cracca), and other species. Recently published Alaskan field degradation data indicates aminopyralid can persist at harmful levels to sensitive non-target species, and soil attenuation is likely primarily driven by sorption of the herbicide to soil particles. This study will characterize soil sorption characteristics and climatic factors to calculate relative contributions to field degradation. This will decrease uncertainty with plant-back intervals and environmental exposure data, for which a data gap is noted in the pesticide use risk assessment.
Animal Health Component
0%
Research Effort Categories
Basic
90%
Applied
10%
Developmental
(N/A)
Goals / Objectives
GoalsInvasive Chokecherry ManagementWe hypothesize that total treatment of Prunus padus trees in a plot will increase the amount of herbicide in soil and non-target damage that occurs from treatment with persistent herbicides. Since short term non-target damage could be tolerated, the information from this project will be used to identify when persistent herbicides should be avoided. Further information will be used to identify when restoration of sites through natural regeneration or revegetation will be successful.Objective: Identify when persistent herbicides should be avoided and restoration of sites through natural regeneration or revegetation is needed.Certified Weed Free Straw ProductionWe hypothesize that persistent herbicides can be used to effectively control broadleaf weeds in grain crops while not damaging later rotations to sensitive species if herbicides are applied during a fallow period followed by two years of grain production prior to planting sensitive crop species. Demonstrating this will result in new opportunities for agricultural producers to increase certified weed free straw, while allowing for rotations to sensitive crops.Objective: Develop new methods for agricultural producers to use persistent herbicides to increase certified weed free straw production while allowing for rotations to sensitive crops.Sorption experimentsWe hypothesize that the attenuation of aminopyralid, clopyralid, triclopyr, and metsulfuron methyl are driven primarily by abiotic partitioning, and that non-target impacts from bioavailable residues are the result of a desorption process. These data will be used to correlate herbicide persistence times to those in the chokecherry management and weed free straw field trials. The data will allow agricultural producers and land managers to determine plant back times for restoration or rotation to sensitive crop species after an herbicide application based on their soil characteristics and environmental factors.Objective: Using soil characteristics and environmental factors predict plant back times for sensitive plant species after use of persistent herbicides.
Project Methods
Invasive Chokecherry ManagementStudy areasAnchorage and Fairbanks, the largest urban areas of Alaska, have large infestations of P. padus. Infestations of P. padus in Anchorage are well documented along the Chester and Campbell Creek greenbelts (AKEPIC 2018). In Fairbanks, infestations exist in small unmanaged natural areas throughout the city.Site and plot selectionSites selected in the Anchorage and Fairbanks areas will have varying densities of P. padus measured as number of stems per area. Sites will be 1 hectare in size and contain plots (5 m radius) with at least 5 m between plots to prevent impacts from overlapping. Plots marked with GPS and center points will be permanently marked with a metal stake and identification tag buried in the ground.TreatmentsTreatments will consist of full and half label rates for triclopyr, aminopyralid, and a no treatment control. All treatments will utilize Basal Oil (Alligare) as a surfactant with a factory added blue dye. Treatments in Anchorage and Fairbanks will be assigned as randomized complete block with 5 blocks and 5 treatments including the control for each block. The Fairbanks and Anchorage treatments will be analyzed in a factorial design to determine if they significantly differ from each other or if the treatments can be combined resulting in 10 total replicates per treatment.Evaluation of target and non-target impactsWithin plots, native and non-native species abundance and diversity will be measured. A census of all woody vegetation > 0.1 m in height will be taken within the plot. We will establish four 1 m2 subplots in each plot in which we will characterize understory herbs and woody vegetation <0.1 m in height. Each subplot will be placed in a North, South, East, or West quadrant of the plot. All plants less ≤ 0.1 meter in height within the subplot will be counted and identified to calculate the abundance of each species within the subplots. Percent cover of each species in the subplot will be visually estimated. These whole and subplot measurements of vegetation abundance will be repeated 1 year after treatment. We will record percent defoliation of P. padus that are > 0.1 m in height one and two years after treatment. Any herbicide damage to non-target plants observed will be scored (Washington State University 2002), and representative samples of impacted plant material will be taken to extract herbicide residues from plant tissues.Soil sampling, and detection of herbicideSoil samples 10 cm in depth will be taken at 8 random locations located within each plot before treatments, and one year after treatments. Approximately 10 g of soil from samples will be used to quantify aminopyralid residues using LC/MS-MS methods at UAA that were optimized in Tomco et al. 2016. A sensitive species (e.g. Crepis tectorum) will be planted in the remaining soil as a bioassay to determine biological availability of herbicide residues.StatisticsChanges in vegetation, soil herbicide residues, and bioassays will be analyzed with a multivariate General Linear Model with a repeated measures design with treatment type, and location as factors, initial P. padus cover and initial native plant cover as covariates. Dependent variables will include the post treatment vegetation measurements of percent defoliation of treated P. padus, change in P. padus cover, change in native plant diversity and abundance from pre-treatment to each year after treatment, the number of time non-target herbicide damage is observed in each plot, change in soil herbicide residues after treatment, and dry mass of bioassay.Certified weed free straw productionStudy areasPlots will be established at the Fairbanks and Matanuska-Susitna Experiment stations.Crop and plot set upExperimental design will allow for characterization of the residual soil properties in a field setting while testing if rotations can provide for continued control without carryover of the herbicide. Plots will be set up with a randomized complete block design using 5 blocks. Treatments will include using full label rates of aminopyralid, clopyralid, MSM+2,4-D, and a no treatment control. Crop rotations used in the trials will include a fallow year, followed by two years of grain, the fourth-year peas will be planted, followed by potatoes in the fifth year. This rotation should allow for the producers to benefit from the nitrogen accumulation of the peas on their most nitrogen dependent crop, potatoes. The MSM+2,4-D treatment plots will have annual applications to the grain in addition to the fallow which is presently the common practice.Residual control of weeds with the herbicides will be tested each year using bioassays with hempnettle and hawksbeard. These bioassays will be coupled with extraction of herbicide from the soils and analytical determination of the quantity present. Additionally, we will test for residual herbicide (aminopyralid and clopyralid) presence in the harvested straw.Soil and plant samplingThree soil samples from each treated plot will be collected during the spring of each season to determine residual concentrations of herbicide. Bioassays will also be performed to determine the potential for non-target damage to sensitive species. After planting and harvest of grain, straw material will be tested for the presence of aminopyralid and clopyralid to determine if herbicide is carried over in plant material from the previous season applications. Testing plants and soil for presence of herbicide will show if soil herbicide concentrations in year two and three are low enough to not carry over in the crop, but high enough to affect target weeds.StatisticsComparisons of non-target damage to rotational species, and control of weeds in these plots will be accomplished using an ANOVA where treatment is the factor. The dependent variables are the soil herbicide residual concentration, straw herbicide residual concentration, and dry mass of Crepis tectorum determined from the bioassays.Pesticide sorption behaviorLab studiesLab studies will characterize the sorption behavior of aminopyralid and clopyralid by determining several commonly-reported indices that can be compared to EPA registration data. These are: sorption affinity (Kd), organic-carbon-normalized distribution (Koc), sorbent capacity, and desorption potential (Schwarzenbach 2005, OECD 2000). Herbicide-free soil samples from soils at field sites in Alaska where the barley trials, and the Prunus trials are located will be collected, bagged, and transported to the Tomco lab at University of Alaska Anchorage. Soil will be dried and sieved through 2mm mesh. To eliminate interfering microbial processes, soil will be sterilized by gamma irradiation. Isotherms will be constructed from as previously identified using the batch equilibration methods (OECD 2000, OPPTS 1998). Batch incubation microcosms will be created; these will consist of a series of serum vials each with 50 g sieved soil with water. Vials are spiked with herbicide at a range of concentrations based off the label rate (0X, 0.01X, 0.05X, 0.1X, 0.5X, 1X, 5X). The samples are incubated at one of three temperatures (5°C, 10°C, 20°C) in triplicate on a rotary shaker for 72 hours to reach an equilibrium phase where herbicide is maximally sorbed to soil suspended in solution. The equilibrium phase is separated by centrifugation, and an aliquot of supernatant is decanted from each vial.The extraction procedure and analysis are outlined in Vasquez et al. 2010 and Mulligan et al. 2015, and we will calculate values similarly as noted in these studies.StatisticsLinear regression will be used to determine the Freundlich parameters values Kf and N, standard errors, and coefficient of determination R2. ANOVA test will be used to determine differences between the soils, desorption isotherms, and treatments with post hoc comparisons.