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The efficacy of the phosphonate fertilizers, Calphos(®) (a.i. calcium phosphonate), Magphos(®) (a.i. magnesium phosphonate and potassium phosphonate) and Phosphoros(®) (a.i. potassium phosphonate) against two species of root knot nematodes (RKN), Meloidogyne javanica and M. incognita is evaluated. Laboratory experiments showed that Calphos(®), Magphos(®) and their main components inhibited egg hatching and caused 100% mortality of the second stage juveniles (J2s) of the two RKN species; the hatching inhibition effects persisted after transferring the egg masses of both species to water. However, Phosphoros(®) (0.5%) did not suppress egg hatching or the survival of J2s of both RKN species. No hatching occurred when egg masses were treated for one week with the nematicide Vydate L(®) (2 ml/l), however, J2s hatched when the Vydate L(®) treated egg masses were moved to water. The glasshouse study indicated that Magphos(®), Calphos(®) and Phosphoros(®) reduced root galling caused by M. javanica by 98, 66 and 47%, respectively, in comparison to the untreated controls. Magphos(®) resulted in the lowest number of root galls formed by M. incognita, the reduction was 84%. In contrast, Calphos(®) and Phosphoros(®) reduced galling by 47 and 39%, respectively. The Magphos(®) treatment resulted in the lowest numbers of egg masses and the lowest reproductive factor (RF) of both nematode species. However, plants treated with Phosphoros(®) resulted in higher foliage weights compared with the application of the other two fertilizers and the untreated plants.