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Evaluating the Impacts of Border Vegetation Patterns on Multifunctional Biodiversity and Crop Production in Washington Blueberry

Herbaceous flowering or woody plant borders are controversial in commercial blueberry (Vaccinium corymbosum) production. Border vegetation has the potential to increase populations of native pollinators and beneficial insects and birds that feed on key blueberry pests, such as spotted wing drosophila (Drosophila suzukii; SWD); however, they may also draw pollinators away from the crop, serve as overwintering and/or refugia sites for SWD, and increase populations of wild birds that feed on fruit and transmit foodborne pathogens. The objective of this project was to explore the impacts of border vegetation adjacent to commercial blueberry fields on multifunctional biodiversity, with an emphasis on pollination services, populations of beneficial and pest insect and bird species, and crop production. The hypothesis is that vegetation adjacent to blueberry plantings will increase multifunctional biodiversity and associated benefits, which will be measured as increased pollinator activity, increased populations of beneficial insects and insect-eating birds (with the potential for biocontrol), and enhanced crop productivity relative to plantings without adjacent border vegetation. However, we also hypothesize that adjacent vegetation will provide refugia for SWD and problematic birds (i.e. species that predate on fruit or transmit food-borne pathogens) that may limit the benefits of border vegetation. We tested our hypotheses in 2017 by comparing pollination services, populations of beneficial and pest insect and wild bird species, and production attributes of blueberry grown with or without adjacent border vegetation on 9 commercial farms in northwest Washington. Our border vegetation treatments include: 1) Control (no vegetation adjacent to the site); 2) Woody perennial vegetation [mixture of woody perennial species including Cedar (Cedrus sp.) and Arborvitae (Thuja sp.)]; and; 3) Herbaceous vegetation [mixture of monocots (e.g., Poa sp. and quackgrass (Elymus sp) and broadleaves (E.g., Taraxacum officinale)]. There were no differences in pollinator abundance, flower visitation rates, or estimated yield and fruit quality across the treatments. Different species of insects and arachnids were collected during a 16-week period using an insect vacuum and apple cider vinegar traps. Virtually no SWD were recovered and populations of all arthropod species declined in the border vegetation after a pesticide application. Yellow sticky cards used to monitor the movement of beneficial and pest insect species suggest there are no differences in their in-field populations by treatment. However, there were overall greater populations of both pest and beneficial insects in the border vegetation relative to in the blueberry field. Habitat-based point-counts were used to evaluate how border vegetation influenced populations of wild bird species. Pest species were observed in all treatments and densities of birds increased with decreasing distance to our border vegetation treatment. Data from this project show that our evaluated border treatments have small to negligible impacts on our measured variables and we did not detect any clear multifunctional benefits associated with our different border vegetation treatments.

Grant Information

  • Project ID: 171
  • Project Status: Complete

2018

  • Principal Investigator(s): Wasko-DeVetter, L.
  • Investigator(s): Arrington, M., Gerdeman, B., Snyder, W.
  • Grant Amount: $31134
  • 2018 Progress Report

Publications

  • DeVetter, L.W., B. Gerdeman, M. Arrington, H. Spitler, B. Snyder, and O. Smith. 2018. How Border vegetation impacts pollination and insect and bird species abundance on Washington blueberry farms. WSU Whatcom Ag Monthly. < https://extension.wsu.edu/wam/how-border-vegetation-impacts-pollination-and-insect-and-bird-species-abundance-on-washington-blueberry-farms/>.
  • DeVetter, L.W., M. Arrington, B. Gerdeman, H. Spitler, O. Smith, and W. Snyder. 2019. Border vegetation has few impacts on multifunctional biodiversity and crop production in commercial blueberry. Canadian Entomologist. In preparation.
  • Smith, O., L.W. DeVetter, and W. Snyder. 2019. Analysis of avian fecal samples from Washington blueberry fields. In preparation.

Additional Funds Leveraged

We collaborated with Catherine Lindell at Michigan State University and applied to the USDA CPPM program in 2018. The title of the grant was: “Cultural management practices as influences on services and disservices provided by birds in fruit crops”. We were unsuccessful, but plan to re-apply in 2019.

Impacts

  • Short-Term: This project provided quantitative data on the impacts of non-flowering border vegetation on multifunctional biodiversity and crop yield/quality in commercial blueberry production systems in Washington. We have shared this information with growers through established outreach mechanisms.
  • Intermediate-Term: The current practice among blueberry growers is to establish border vegetation to mitigate drift from pesticide applications next to sensitive areas and to provide a riparian buffer for the protection of waterways. These practices are often viewed as regulatory necessities. Seldom do growers mention or realize the potential for border vegetation to improve pollination and biocontrol, or to conversely worsen pest problems by harboring pest insects and frugivorous birds. Our intermediate-term goal is to pursue federal-competitive funding to further study and describe ways to maximize benefits, and minimize any harms, resulting from border plantings alongside blueberry fields. To date, however, our preliminary results have not supported the conclusion of any impact (positive or negative) of border vegetation on our measured variables. Flowering borders that are intentionally established for pollination services and with a bloom that overlaps with blueberry may result in more positive findings and should be investigated. However, there are constraints with regards to integrating these into commercial blueberry production. Locations to install flowering borders will need to be identified and managed, which growers may be reluctant to do. Additionally, our data suggests that there is the potential that regular pesticide applications could limit the benefits of these flowering borders.
  • Long-Term: Blueberry productivity in western Washington is lower on a per area basis compared to eastern Washington. Much of this has been attributed to constraints during pollination, which could be improved through more resilient pollination systems. Insect pest pressure from SWD is also more severe in western Washington, resulting in regular insecticide applications. Over time, border vegetation that shows a detectable benefit may lead to more resilient pollination systems due to increased biodiversity from adjacent vegetative borders, which may increase yields. Beneficial insects and birds may also be better conserved, which may lessen SWD infestations and lead to reduced pesticide applications. Growers’ perception of border vegetation may also be enhanced to encompass how they impact pollination services, biocontrol, and crop productivity. However, the potential insect-mediated benefits may be lost if growers maintain their robust insecticide programs, as we observed declines in insect populations in our study that coincided with insecticide application. Improved integrated pest management (IPM) for SWD may help reduce the need for these insecticide applications.