Fifteen experimental trials were carried out under greenhouse conditions to evaluate the efficacy of preventative treatments based on phosphite salts on the following pathosystems: tomato/Phytophthora nicotianae, zucchini/P. capsici, lettuce/Fusarium oxysporum f.sp. Iactucae, rocket/Fusarium oxysporum f. sp. raphani, wild rocket/Plectosphaerella cucumerina and basii/Peronospora belbahrii. The possible use of phosphite salts in nursery cultivation systems is considered in comparison with chemical fungicides. Phosphites-based products reduced 66-88% and 56-72% the severity of Phytophthora crown root rot of tomato and zucchini, respectively. Four application with the phosphites-based products provided a disease reduction of Fusarium wilt of lettuce from of 33 to 83% and of 45 to 68% on cultivated rocket. These products provide the most constant results when applied in three treatments against Plectosphaerella cucumerina with a disease reduction ranging between 34%-82%. Phosphite-based products showed results statistically similar to mefenoxam when tested against downy mildew of basil. Their contribution to disease management can be very interesting, because they can complement other control measures.