ASHS 2024 Conference

Utilizing single-use polyethylene (PE) mulch in agriculture is controversial due to concerns with plastic waste generation and pollution. An alternative option to PE mulch is hydromulch (HM), which is paper-based, biodegradable, and potentially could be certified organic. HMs can be produced from water, recycled paper, and organic-approved tackifier(s). The objective of this experiment was to determine the efficacy of different HM formulations on yield, fruit quality, mulch coverage, and weed suppression in a mature planting of northern highbush blueberry (Vaccinum corymbosum ‘Valor’) grown in eastern Washington. Using a randomized complete block design with four replications, four mulch treatments were tested: (i) HM with 4% guar gum, (ii) HM with no tackifier, (iii) paper mill slurry, and (iv) woven PE mulch (hereafter “weedmat”). The papermill slurry was made by agitating recycled paper with water and sodium hydroxide until the paper was pulped and ink removed. Yield, fruit firmness, titratable acidity as percent citric acid, total soluble solids, and pH were similar across all treatments. Mulch coverage measured as percent soil exposure was greatest for the slurry, followed closely by the 4% tackifier and no tackifier treatments. Weedmat had the lowest percent soil exposure. All treatments mostly suppressed dicot weeds, however, the no tackifier and slurry treatments had the greatest dicot numbers. The 4% tackifier suppressed nearly all dicots. HMs struggled to suppress monocots, with the slurry and no tackifier treatments performing the worst at monocot suppression. The 4% tackifier treatment was better than the other HM formulations, however, it had little-to-no effect on nutsedge (Cyperus esculentus) while weedmat suppressed all monocots. Weed biomass data revealed different patterns with the 4% tackifier treatment having similar weed biomass compared to the slurry and no tackifier treatments. This was likely due to lack of competition, as when weeds penetrated the 4% treatment they did not have other plants to compete with, and thus accrued biomass much faster than weeds in the slurry and no tackifier treatments. Although weed and fruit quality was maintained, future research should focus on increasing HMs ability to suppress nutsedge and other vigorous weed species.