Organic matter inputs, including plant residues, manure, and composted organic wastes, have been shown to significantly reduce the severity of a wide variety of root diseases, including those caused by Pythium spp., in natural systems (Perrin, 1986) and field systems (Lewis et al, 1992). Compost amendments have also been shown to reduce the incidence of bacterial spot in field tomato (Miller et al, 1998). Organic matter (OM)- mediated suppression of foliar diseases might be due to the induction of induced systemic resistance (ISR) by microorganisms supported by the OM. Induced resistance is a “state of enhanced defensive capacity” triggered by specific contact stimuli, whereby the plant’s active defenses are activated by a subsequent challenging pathogen (van Loon et al. 1998).