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Determining the Effect of Biodegradable and Living Mulches on Annual Weeds and and Growth of Newly-planted Blueberry

In a newly planted blueberry trial, ‘Draper’ plants were transplanted from 1-gal pots into the field in March 2015.  Greenhouse-grown living mulch plants, creeping buttercup (Ranunculus arvensis L.) and sweet woodruff (Galium odoratum (L.) Scop.), were transplanted to a density of 1 plant/ft2 at the same time as blueberry.  Other plots were treated with 5 cm of sawdust or by an experimental BDM made of black spunbond polylactic acid.  These treatments were applied to cover all bare soil.  Soil in the fifth treatment was left bare.  BDM provided good to excellent weed control, reducing weeding time by 64% over the two years in the trial as compared to bare ground plots, including a 90% reduction in 2015.  Sawdust and creeping buttercup also reduced weeding time by 57 and 41%, respectively, performing better than sweet woodruff (increased weeding time by 15%).  Meadow vole (Microtis spp.) damage was extensive in all plots by the end of the second year and was considered to be the primary cause of blueberry mortality and was responsible for poor plant growth.  Number of live blueberry plants at the end of two growing seasons was greatest in sawdust (96% survival), contrasted with 26 to 48% survival in the other treatments.  Shoot and root biomass after two growing seasons was also maximized in sawdust-grown blueberry (331 and 1085 g/plant, respectively) compared to 220 g/plant or less for shoots or 448 g/plant or less for roots among the other treatments. Despite this, 85% of sawdust-mulched plants were considered to be unhealthy due to poor growth and early senescence of leaves.  Blueberry root and shoot growth was best in BDM and sawdust plots, indicating that these living mulches were not a good option in newly planted blueberry.  When blueberry plants were characterized according to their visible health, biomass of unhealthy blueberry plants was only 8 to 29% of the biomass from healthy blueberry plants.  If used in organic production, managers will have to take special precaution to manage vole activity regardless of mulch type to improve the likelihood of successful blueberry plant establishment.  In a separate trial in well-established ‘Duke’ blueberry, creeping buttercup and sweet woodruff were transplanted as described above in March 2015 and their effects on weeds and blueberry were compared to those from sawdust mulch.  Living mulches did not affect hand-weeding time in 2015, or mean berry weight and berry yield in either year.

Grant Information

  • Project ID: 150
  • Project Status: Complete

2015

  • Principal Investigator(s): Miller, T.
  • Investigator(s): Wasko-DeVetter, L.
  • Grant Amount: $12,839

2016

  • Principal Investigator(s): Miller, T.
  • Investigator(s): Harteveld, D., Wasko-DeVetter, L.
  • Grant Amount: $10,483

2018

Publications

A poster was presented at the XI International Vaccinium Symposium held in Orlando, Florida on April 10-14, 2016 (full-text article of 2015 results was accepted for publication by Acta Horticulturae:  Miller, T.W. and L.W. DeVetter.  2017.  Effectiveness of living and compostable mulches for weed control in Pacific Northwest highbush blueberry).  A journal article (likely for HortScience) for the newly planted blueberry trial is currently being written by Miller and DeVetter.

Additional Funds Leveraged

Project co-funding was unsuccessfully sought from Western Region Integrated Pest Management Center and the Washington Blueberry Commission.  DeVetter and Miller (joined by WSU faculty Sablani and Hoheisel, and WSU postdoc Harteveld) also unsuccessfully applied for an Organic Agriculture Research and Extension Initiative (OREI) proposal for more extensive testing of compostable and living mulches in 2016.

Impacts

  • Short-Term: Creeping buttercup was very effective at reducing growth of other weeds, but young blueberry root and shoot biomass were dramatically reduced in that planting.  Sweet woodruff was not as effective on controlling weed growth as buttercup, but blueberry growth was as poor in sweet woodruff plots as in buttercup.  Compostable mulch gave outstanding weed control, although blueberry biomass was similarly reduced as in living mulch plots.  Taking weed control and blueberry growth into consideration, then, sawdust was the best mulch for blueberry establishment of young blueberry plantings.
  • Intermediate-Term: Compostable mulches can provide effective weed control in newly planted blueberry, provided control of voles is adequate.  Because of negative effects on blueberry growth and survival, living mulches are not recommended for young blueberry plantings.  In established blueberry, living mulch did not significantly affect yield or weeding time, and therefore do not appear to be worth the time and cost of establishment as compared to sawdust mulching.