Herbicide weed control is difficult in the first years of perennial crop establishment or in minor crops, and plastic sheet mulches can leave persistent residues. Liquid spray-on mulch (hydromulch) might be a solution in these cases. To test three hydromulch formulations on perennial weed emergence, greenhouse assays were conducted for two years in two localities to evaluate their rhizome sprouting and shoot emergence. Data, obtained from a completely randomized block design, were analyzed by means of generalized linear mixed models with binomial distribution and logit link function; the effects of hydromulch, species, and their interaction were considered fixed, while the other sources of variation (i.e., locality, year, block and rhizome length) were considered random. All three hydromulches, based on wheat straw, rice husk, and used substrate for mushroom cultivation, were capable of reducing rhizome sprouting of all four species tested when compared to the non-mulched treatment. Many rhizomes sprouted but were trapped under the mulch layer, especially those of Paspalum dilatatum (87%), Cynodon dactylon, and Sorghum halepense (around 50%), while Cyperus rotundus was least affected by the hydromulch treatments (16%). All three blends showed promising results in the reduction of perennial weed emergence, warranting field trials to test combined weed management strategies.