Halophytes are gaining considerable attention due to their applications in saline agriculture, phytoremediation, medicine, and secondary metabolite production. This study investigated the bioactive components present inSilene uniflora(sea campion) hydromethanolic extract, and their antimicrobial activity was evaluated both in vitro and ex situ against two strawberry phytopathogens, namelyBotrytis cinerea(grey mold) andColletotrichum nymphaeae(anthracnose fruit rot). The main identified phytochemicals were mome inositol, saturated fatty acid esters, and cyclotetracosane. In vitro tests demonstrated complete inhibition of the growth ofB. cinereaandC. nymphaeaeat extract concentrations of 1000 and 1500 μg·mL−1, respectively, with an activity comparable to that of fosetyl-Al and substantially higher than that of azoxystrobin. This activity was improved upon conjugation with chitosan oligomers (COS), yielding inhibition values of 750 and 1000 μg·mL−1. The COS-S. unifloraconjugate complexes were then tested as protective treatments for postharvest storage of strawberry fruit, resulting in high protection against artificially inoculatedB. cinereaandC. nymphaeaeat doses of 3750 and 5000 μg·mL−1, respectively. The reported results open the door to the valorization of this halophyte as a source of biorationals for strawberry protection.