Hydromulches in Organic Strawberry Production: Effects on Densities of Insect Pests and Natural Enemies

Liquid‐sprayable cellulose hydromulches (HM) are alternatives to plastic polyethylene (PE) mulches for weed suppression in organic agriculture. However, their impact on arthropod pests and natural enemies remains unexplored. Various HMs made of shredded newsprint, water and guar gum were compared against white‐on‐black PE mulch, paper sheet mulch, a weedy check and a weed‐free control. Four HM treatments combining application rates (low: 5800 or high: 8700 kg dry weight ha −1 ) and colour intensity (dark or light) were tested in raised‐bed, drip‐irrigated organic strawberry crops at two sites: Absaraka and Fargo, ND. Densities of insect pests and natural enemies were measured via pitfall traps and pest‐specific sampling methods. Mulch treatments affected Lygus and Nysius bugs densities (Hemiptera: Miridae, Lygaeidae) via indirect positive effects of weed density. There were no effects of mulch on densities of spotted‐wing drosophila [ Drosophila suzukii Matsumura (Diptera: Drosophilidae)] or fruit infestation. Activity‐density of harvestmen, spiders, and large carabid beetles was similar among mulch treatments, likely reflecting high mobility across uneven surfaces. Activity‐density of medium‐ and small‐sized carabid beetles was typically highest in weed‐free or weedy plots. HMs appeared to have disrupted the movement of medium‐ and small‐sized carabid beetles at one location, although impacts on other arthropods appeared to be minimal or related to weed density. HMs are a promising weed management tool in organic strawberry systems, but our findings reveal complex relationships between mulch physical properties, weed communities, and arthropods that need to be considered.