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Plastic mulches suppressed weeds and increased red raspberry yield in a spring-planted field

Volume 8 Issue 9


Huan Zhang1, Carol Miles1, Shuresh Ghimire2, Chris Benedict3, Inga Zasada4, and Lisa DeVetter1

1Washington State University, Northwestern Washington Research & Extension Center, Mount Vernon, WA
2University of Connecticut, Tolland County Extension Center, Vernon, CT
3Washington State University, Whatcom County Extension, Bellingham, WA
4USDA-ARS, Corvallis, OR


Transplanted red raspberries on plastic mulch
Figure 1. TC transplants grown with a biodegradable plastic mulch.


  • Tissue culture (TC) raspberry transplants can be difficult to establish and are weak competitors with weeds.
  • Polyethylene (PE) mulch is used to manage weeds, minimize soil moisture loss, modify soil temperature, and promote yield and quality of fruits and vegetables. However, PE mulch removal and disposal are both costly and challenging (Lamont, 2017).
  • Biodegradable plastic mulch (BDM) can be an alternative to PE mulch and is designed to biodegrade in soils after incorporation, thereby reducing the economic and environmental problems associated with PE mulch removal and disposal (Fig. 1; ASTM, 2018; Miles et al., 2017).
  • Few studies have tested BDMs and PE mulch in perennial production systems, such as floricane red raspberry.
  • Root lesion nematode (Pratylenchus penetrans; RLN) is a plant-parasitic nematode with a wide host range, including raspberry (Castillo and Vovlas, 2007; Zasada et al., 2015).
  • Results are conflicting from previous reports regarding the impacts of plastic mulches on RLN populations (Gerbrandt, 2015; Miller, 1976; Miller and Waggoner, 1963). There is a concern that increased soil temperatures under BDMs and PE mulch could increase RLN reproduction and subsequent population densities.


  1. Evaluate establishment, growth, and yield of TC raspberry grown with BDMs and PE mulch in comparison to a bare ground (BG) control (herbicides and hand weeding – industry standard practice).
  2. Assess weed incidence and population densities of RLN in raspberry grown with BDMs and PE mulch in comparison to BG control.

Materials and Methods

Experimental Design:

  • An on-farm experiment was established in Lynden, WA, as a randomized complete block design in May 2017 with 6 treatments including 4 BDMs (BASF and Novamont both at 0.5 and 0.6 mil thicknesses), PE mulch (1 mil thickness), and BG control (Table 1).
  • Treatments were replicated five times. The field was planted with ‘WakeTMField’ raspberry.

Table 1.


Data Collection:

  • Plant growth was measured monthly as primocane height and number from 10 plants per plot from May to Oct. 2017 and Sept. 2018 (Fig. 2).
  • Primocane emergence was measured from a 30 ft region in each plot in July 2018.
  • Fruit yield was determined from 13 harvests from June 29 to Aug. 10, 2018.
  • Cumulative weed number as well as fresh and dry shoot biomass present within an 11 ft2 area were recorded monthly from May to Oct. 2017.
  • RLN densities were determined in soil in May 2017 and both soil and roots in Oct. 2017 and May and Sept. 2018 (Fig. 3).

Figure 2. Comparison of plant height on July 6, 2017 (50 days after transplanting); bare ground (BG) control (A) and a plastic mulch treatment (B).


Figure 3. Root collection for root lesion nematode extraction.


  • Average primocane height and number measured in Oct. 2017 were 14 in. and 5 canes/hill greater, respectively, in all mulched treatments relative to the BG control (Figs. 4A and 4B).
  • Average yield (8900 lbs/acre) across all mulched treatments (BDMs and PE mulch) was 34% higher than the BG control (6200 lbs/acre) in 2018.
  • Primocane height measured in Sept. 2018 did not differ among treatments.
  • Primocane emergence measured in July 2018 was lower in PE and Novamont 0.5 (a BDM) compared to the BG control (Table 2).
  • Weed incidence was reduced in all mulched plots compared to the BG control from May to Oct. 2017 (Fig.5).
  • Soil temperature was on average 2.3 °F higher in all mulched treatments compared to the BG control during the 2017 growing season (data not presented).
  • RLN soil and root population densities in Sept. 2018 samples were greater when soil and plants were treated with PE mulch (350 RLN/100g soil and 2605 RLN/g root); no symptoms of nematode feeding were observed on the plants.

Figure 4. Primocane height (A) and primocane number (B) of ‘Wake™Field’ raspberry in 2017 grown with polyethylene (PE) and biodegradable plastic mulches (BASF and Novamont treatments) compared to bare ground (BG) during establishment. NS, **, *** indicate nonsignificant or significant differences at P≤0.001 or 0.0001, respectively, using a means comparison with a Tukey’s honestly significant difference test.

Table 2.


Figure 5. Cumulative weed number per 11 ft2 for establishing raspberry grown with polyethylene (PE) and biodegradable plastic mulches (BASF and Novamont treatments) compared to bare ground (BG) in 2017. * Indicates significant difference at P<0.05 using a non-parametric multiple comparisons Wilcoxon test.

Discussions & Conclusions

  • Plants grown with BDMs and PE mulch exhibited greater primocane height and number during their first year of growth and had higher yields than the BG control.
  • Few weeds were observed in all mulched treatments, so no hand weeding was needed. However, growers hand weeded the BG plots 3 times during 2017 growing season. Therefore, mulches eliminated the need for hand weeding labor at this experimental site.
  • While RLN population densities were higher under PE mulch, there were no observed effects of nematode feeding on plant health.
  • Overall, BDMs and PE mulch performed better than bare ground in a commercial red raspberry field established using TC transplants.

Future work

  • Yield will be determined in 2019 from all treatments.
  • Root and soil samples will be collected in Sept. 2019 for RLN quantification.
  • Mulch removal and disposal options for PE will be explored in Whatcom County, WA.
  • An economic analysis of using plastic mulches (BDMs and PE mulch) in red raspberry production will be generated.
  • A fall-planted trial with BDMs and PE mulch is on-going in Lynden, WA.
  • Potential products that can promote BDM surface and in-soil degradation are under investigation at WSU NWREC, Mount Vernon, WA.
  • TC red raspberry grown with different mulches designed for multi-seasonal purposes is being evaluated at WSU NWREC, Mount Vernon, WA.
  • Information will be shared with stakeholders as it becomes available.


American Society for Testing and Materials (ASTM). 2018. Standard test method for determining aerobic biodegradation of plastic materials in soil. ASTM D 5988-18. ASTM International, West Conshohocken, PA.

Castillo, P. and N. Vovlas. 2007. Pratylenchus, Nematoda, Pratylenchidae: diagnosis, biology, pathogenicity and management. Nematol. Monogr. Perspect. 6:1–530.

Gerbrandt, E. 2015. New techniques for getting raspberries and strawberries off to a better start. 2015 Lower Mainland Horticulture Improvement Association Horticulture Growers’ Short Course. Accessed on 10 June 2019 at:

Lamont, W.J. 2017. Plastic mulches for the production of vegetable crops. A guide to the manufacture, performance, and potential of plastics in agriculture. Elsevier.

Miles, C., L. DeVetter, S. Ghimire, and D.G. Hayes. 2017. Suitability of biodegradable plastic mulches for organic and sustainable agricultural production systems. HortScience 52:10-15.

Miller, P.M. 1977. Interaction of plastic, hay and grass mulches, and metam sodium on control of Pratylenchus penetrans in tomatoes. Journal of nematology, 9(4):350.

Miller, P.M. and P. E. Waggoner. 1963. Interaction of plastic mulch, pesticides and fungi in the control of soil-borne nematodes. Plant and Soil, 18(1):45-52.

Zasada, I.A., J.E. Weiland, Z. Han, T.W. Walters, and P. Moore. 2015. Impact of Pratylenchus penetrans on establishment of red raspberry. Plant Dis. 99:939-94.



Thank you to Sean Watkinson, Ed Scheenstra, Matt Arrington, Clara TeVelde, Nadia Bostan, Weixin Gan, Qianwen Lu, and Washington raspberry growers for their support. We are also grateful for the support and assistance of Juan Garcia and Riley Spears at Rader Farms. Also, we would like to acknowledge the entities below for funding and materials support:

Washington red raspberry commission logo


Bio360 logo


BASF company logo


Novamont company logo


Washington State Department of Agriculture logo


Washington State Commission for Pesticide Registration logo

This study was published in 2019.

Zhang, H., C. Miles, S. Ghimire, C. Benedict, I. Zasada, and L. DeVetter. 2019. Polyethylene and biodegradable plastic mulches improve growth, yield, and weed management in floricane red raspberry. Sci. Hort. 250:371-379.

For more information: free feel to contact Huan Zhang ( or Lisa DeVetter (

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