Hydromulch suppresses dicot but not monocot weeds and maintains yield and fruit quality in established blueberry

Authors: WEISS, BENJAMIN - Washington State University; MAUPIN, BRIAN - Washington State University; BAJWA, DILPREET - Montana State University; DURADO, ANDREW - Montana State University; Weyers, Sharon; AHMAD, WAQAS - North Dakota State University; GRAMIG, GRETA - North Dakota State University; WASKO DEVETTER, LISA - Washington State University

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/15/2025
Publication Date: 10/1/2025
Citation: Weiss, B., Maupin, B., Bajwa, D.S., Durado, A., Weyers, S.L., Ahmad, W., Gramig, G., Wasko Devetter, L. 2025. Hydromulch suppresses dicot but not monocot weeds and maintains yield and fruit quality in established blueberry. HortScience. https://doi.org/10.21273/HORTSCI18739-25.
DOI: https://doi.org/10.21273/HORTSCI18739-25

Interpretive Summary: Woven plastic weedmat is widely used in highbush blueberry (Vaccinium corymbosum) production due to its capacity to suppress weeds, improve soil microclimates, and increase yields. However, weedmat and similar plastic mulches can result in soil contamination or landfill costs. Research is needed on hydromulches, a closed-loop, sprayable, biodegradable technology that could provide a sustainable alternative for growers while preserving the horticultural benefits of plastic mulch. The objective of this experiment was to evaluate the effects on weed suppression, yield, fruit quality, tissue nutrient status, and seasonal durability under two hydromulch formulations compared to a weedmat control in an established planting of ‘Valor®’ blueberry. The hydromulch formulations tested were a cellulosic paper base, or a paper base with 4% guar gum tackifier acting as a glue in 2023 and 2024 in a dry climate. Number and biomass of monocot weeds were greater under hydromulches compared to the weedmat, but greater numbers of dicot weeds under hydromulches were relatively suppressed in comparison to monocots. Additionally, blueberry yield and fruit quality were not different among hydromulchs and weedmat. Leaf tissue nutrient varied from established standard ranges between years but were not influenced by hydromulch treatment. The suppression of dicot weeds, and lack of effect on yield, fruit quality and plant nutrition in an established blueberry field indicate that hydromulches are a promising substitute for plastic weedmat mulches. Organic blueberry producers and other weed scientists will benefit from better understanding of weed control with biodegradable and organically-certifiable alternatives to plastic mulch.

Technical Abstract: Woven plastic mulch ("weedmat") is widely used in highbush blueberry (Vaccinium corymbosum) production due to its capacity to suppress weeds, improve soil microclimates, and increase yields. However, weedmat and other mulches made with non-biodegradable plastics are difficult to recycle, resulting in large amounts of plastic waste being landfilled. Complete removal of plastic mulch from fields is challenging, resulting in macro- and micro-plastic contamination of agricultural soils and the surrounding agroecosystem. While soil-biodegradable plastic mulches address many of these issues in conventional agriculture, National Organic Program regulations in the United States prohibit their use in organic systems. Hydromulch is a closed-loop, sprayable, biodegradable mulch technology that could provide a sustainable alternative for organic growers while preserving the horticultural benefits of plastic mulch. However, research on hydromulch efficacy in perennial systems is scarce. The objective of this experiment was to ascertain the effects of multiple hydromulch formulations on weed suppression, yield, fruit quality, tissue nutrient status, and seasonal durability [measured as percent soil exposure (PSE)] in an established planting of ‘Valor®’ blueberry. Two hydromulches formulated a cellulosic feedstock with or without a 4% guar gum were compared to a weedmat control in 2023 and 2024 in a dry climate. Hydromulch formulations had a significantly greater number and biomass of monocot weeds when compared to weedmat due to higher levels of seasonal mulch deterioration and monocot growth habit. Yield and fruit quality in hydromulch treatments were similar to the weedmat, although the 4% guar gum hydromulch had one-third lower yield relative to the no tackifier hydromulch treatment in 2023. Significant but inconsequential deviations from leaf tissue nutrient standards were observed but were not attributed to hydromulch treatment. This study illustrated that the evaluated hydromulch formulations suppressed dicot but not monocot weeds while maintaining yield and fruit quality in an established blueberry field. Future hydromulch research should focus on increasing its mechanical properties to enhance monocot weed suppression, the cost-benefits of hydromulch adoption, and understanding any soil health implications of hydromulch use.