In Florida, Tetranychus urticae Koch, the twospotted spider mite (TSSM), is the most detrimental arthropod pest in strawberry (Fragaria X ananassa Duchesne). Chemical tactics are available to control this pest but they must be repeated throughout the season. Non-chemical control strategies rely on the use of certified plants, resistant varieties, and the use of predatory mites. Biological control provides a practical option to pesticides. The objective of our research was to study the effectiveness of two species of predatory mites, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus McGregor in the field in the 2003-04 and 2004-05 seasons. The on-farm experiment was carried out in two growers’ fields in three sites: central and northern Florida, and South Carolina. Predatory mites were released at a rate of one predatory mite per plant when approximately 10% of the leaflets were infested with one or more TSSM. Phytoseiulus persimilis, is a better suited for central Florida than is N. californicus; however, N. californcius densities seem to develop more slowly than densities of P. persimilis. In northern Florida and Charleston, S.C., N. californicus provided better control of TSSM than P. persimilis. Marketable yields were significantly higher in treatments with N. californicus during the 2003-04 field season in northern Florida. The population dynamics of the TSSM and predatory mites are presented. Our data suggest that early releases of predatory mites, sometimes in combination with miticides, can provide season long control.