Application of Biodegradable Mulches in Day-neutral Strawberry Grown in Western Washington

Biodegradable mulches (BDMs) were introduced as an alternative to polyethylene (PE) mulches, which have economic and environmental challenges regarding costly removal and disposal.  Biodegradable mulches may provide the same horticultural benefits as PE mulches, but are engineered to degrade in soils upon incorporation.  Yet, BDMs have undergone limited testing, including with day-neutral strawberry (Fragaria × ananassa) typically grown with PE mulch in plasticulture.  The objective of this study was to evaluate whether BDMs are suitable for day-neutral strawberry production, with regional specificity to western Washington.  To accomplish this, a randomized complete block split plot experimental design was established in Spring of 2014 and 2015 at the Washington State University Research and Extension Center located in Mount Vernon, Washington.  The study consisted of five main plot treatments, replicated four times.  Treatments included: 1) a starch based BDM; 2) a prototype BDM; 3) a cellulose based BDM; 4) a PE positive control; and 5) a bare ground negative control.  Cultivar was the split plot factor and consisted of ‘Albion’ and ‘Seascape’.  Data collected includes crop yields, in-season mulch deterioration and intactness [recorded as percentage visual intactness (PVI)], and in-soil mulch degradation.  Yields were on average greater for ‘Seascape’ grown with PE mulch, while ‘Albion’ was less sensitive to the mulch treatments.  In both years of the study, yields were similar among the starch, prototype, and cellulose BDMs for ‘Seascape’ and ‘Albion’, while overall yields tended to be reduced for both cultivars in the bare ground plots.  For PVI, the starch and cellulose BDMs performed similarly in 2014 and together averaged 90% PVI compared to 98% PVI for the PE control by Sept. 30 (the last date of PVI data collection in 2014 and 2015).  The cellulose BDM deteriorated more rapidly in 2015, largely due to the effects of strong winds, and had a PVI of 64% by Sept. 30.  The starch BDM and PE mulch performed similarly in 2015, with 93% and 97% PVI by Sept. 30, respectively.  The prototype BDM deteriorated rapidly in 2014 (7.5% PVI by Sept. 30) and was replaced with a different formulation by the manufacturer in 2015 that had longer persistence in the field (62% PVI by Sept. 30).  Evaluations of in-soil mulch degradation are ongoing.  Results to date demonstrate BDMs perform differently based on their formulation, but are suitable for day-neutral strawberry production in western Washington.