Application of Biodegradable Mulches in Small Fruit Production

Lisa W. DeVetter, Assistant Professor in Small Fruit Horticulture


Figure 1.'Meeker' raspberry grown with a BDM.  Photo taken at Honcoop Farms.

Plastic agricultural mulches based on polyethylene or polypropylene have become an industry standard for specialty crop production due to the ability of these mulches to effectively control weeds, minimize soil moisture loss, modify soil temperatures for optimal growth, and promote earlier and greater yields of high quality crops.  However, removal and disposal of plastic mulch is labor intensive and expensive, leaving some growers to resort to stockpiling, landfilling, burying, and illegally burning mulches.  Biodegradable mulches (BDMs) offer the opportunity to minimize some of the economic, environmental, and human health costs of plastic mulches and their associated disposal.  BDMs are engineered to undergo abiotic weathering and subsequently biodegrade upon incorporation in soils through microbial-aided processes.  Some BDMs deteriorate in as little as 4-13 months, but the duration of time is contingent upon the manufacturing of the BDMs and the environment it is utilized in.  The WSU Small Fruit Horticulture (SFH) program has begun investigating the application of BDMs in small fruit production in western Washington.  Specific crops we are focusing on include tissue-culture (TC) red raspberry, blueberry, and day-neutral strawberry.


Red Raspberry

As TC cultivars of red raspberry are adopted by industry, it is important to develop good horticultural practices to ensure their quick and rapid establishment.  Mulches, including select BDMs, may have application in promoting the establishment of TC raspberry by minimizing weed pressures and optimizing the soil environment to promote their growth.  BDMs grown with ‘Wakefield’ are currently being trialed at Honcoop Farms (Fig. 1) and we look forward to more research assessing the potential utility of BDMs in raspberry.



Highbush blueberry is typically grown with sawdust or bark mulch.  However, many systems are exploring the application of landscape fabrics (aka, “weedmat”), which are typically made of polypropylene and are not biodegradable nor compostable.  These materials offer many horticultural advantages, but also contribute to the generation of waste.  Dr. Miller and I are investigating alternative weed management systems and one of our treatments includes a fully compostable mulch made of spunbound poly(lactic acid), or SB-PLA, which is made of nonwoven biobased polymers.  This material is more durable than several of the other BDMs available on the market.  This project was initiated in 2015 and we will be assessing the influence this material has on crop growth, weed control, as well as in-field durability and longevity (Fig. 2).  This particular project is funded through WSU’s BIOAg program.


Day-Neutral Strawberry

Conventional production of day-neutral strawberry is dependent on polyethylene based plastics, which subsequently produces large volumes of plastic waste.  My graduate student, Mr. Faustich, and I, along with our collaborators Drs. Miles and Sablani, are testing the application of three BDMs at the WSU-NWREC.  In this experiment, three BDMs are being grown with ‘Seascape’ and ‘Albion’ strawberry and the BDMs under investigation include: 1) a corn-starch based film; 2) a bio-based polyhydroxyalkanoate (PHA) based film; and 3) a cellulose-based mulch (organic approved).  The influence of these materials on crop growth, yield, fruit quality, and weed management are being compared to polyethylene plastic mulch and no mulch controls.  We are in the second year of this experiment and so far have observed that all mulches provided adequate weed control (Fig. 3), maintained yield, and were better when compared to the non-mulch control.  The PHA-based mulch deteriorated faster than the other treatments, which may be problematic when trying to maintain the productivity of this system and we are subsequently looking at alternative formulations of PHA-based mulches in 2015.  This experiment is in the second year phase and additional data are being collected and analyzed.  So far, data suggests BDMs are a good alternative to plastic mulches in day-neutral strawberry production in western Washington.  This project has been funded through WSU’s Emerging Research Issues program.



Special thanks to BDM collaborators, including Dr. Carol Miles (Vegetable Horticulture, WSU), Dr. Shyam Sablani (Biological Systems Engineering, WSU), Dr. Doug Hayes (Polymer Chemist, University of Tennessee), Dr. Tim Miller (Weed Science, WSU), Mr. Curtis Faustich (M.S. Graduate Student in DeVetter’s SFH program), Mr. Sean Watkinson (SFH Technician), and Mrs. Rachel Weber (SFH Assistant).  Also, special thanks to Mr. Randy Honcoop (grower cooperator) and collaborating BDM manufacturers.




Figure 2. 'Draper' blueberry grown with SB-PLA, a fully compostable BDM made of biobased and non-woven materials. Photo taken March 30, 2015.

Figure 3. 'Albion' strawberry grown with four mulch treatments, including (numbers in the pictures correspond with the provided treatment number): 1) corn-starch based BDM film; 2) a bio-based polyhydroxyalkanoate (PHA) based BDM film; 3) a cellulose-based BDM (organic approved); and 4) polyethylene plastic.  Photos taken on May 30 and July 31, 2014, demonstrate the rate of visual deterioration and effect on crop growth.