Polyethylene and soil-biodegradable plastic mulches in raspberry production

Floricane raspberry (Rubus ideaus) growers in the Pacific Northwest region of North America are adopting plastic mulch for improved establishment of raspberry planted as tissue culture transplants. Plastic mulch is traditionally made with non-degradable polymeric feedstocks (polyethylene or PE), which leads to accumulation of plastic waste at the end of the production cycle. Soil-biodegradable plastic mulch (BDM) is an alternative to non-degradable mulch and provides similar horticultural benefits without the waste generation but has undergone minimal study in perennial systems. We evaluated PE and BDMs in both spring- and summer-planted raspberry systems. Both mulch types led to increased growth and yields in spring-planted systems relative to the non-mulched control, which is attributed to increased weed control, soil temperature, and moisture conditions. No yield gains were observed in the summer-planted system, although both mulch types provided weed control and reduced the need for herbicides and hand weeding. Woven plastic mulches were also evaluated for multi-year mulching in spring-planted raspberry and provided similar yield benefits as PE and BDMs; however, they are more costly and can reduce primocane growth. Risk and uncertainty assessments among raspberry growers indicate that market and production risks are of greatest concern when it comes to mulch adoption. Sources of production risks mentioned by growers include impacts of plastic mulches on soilborne diseases and growth of roots and canes, while durability and degradability were uncertainties identified specific to BDMs. The higher purchase cost of BDMs has led growers to assume they are less economical despite greater costs associated with PE mulch removal and disposal. As a result, growers are adopting PE mulch for their horticultural benefits and perceived low risk. This research highlights the benefits of mulching in perennial raspberry, as well as future areas of research to support sustainable utilization of plastic mulches.