Humic and fulvic acids were extracted from compost and biogas manure by alkaline (either NaOH 0.5 N or KOH 1 N), and tested against the root – knot nematode, Meledogyne incognita, in vitro and in vivo on both tomato and cow pea and compared with the nematicide, vydate. In vitro vydate at double application dose was the best treatment for inhibiting hatch (47.37%, 45.7% inhibition) with humic and fulvic acid respectively, and was significantly more effective than all others treatments, Humic acid extracted from biogas by NaOH (1 ml L-1 ) was the least effective treatment for inhibating hatch, but humic extracted from compost by KOH (2 ml L-1) was significantly better than the other treatments in reducing the number of surviving juveniles. Humic acid achieved the highest percentage of nematode inhibition (26.09%) in compared with fulvic acid extracted from compost by NaOH in which it was low effective for inhibiting hatch. On the other hand fulvic acid extracted from biogas by KOH was the best treatment in reducing the number of surviving juveniles and achieved up to 45.1 % inhibition and was significantly more effective than all others treatments. In vivo, fulvic acid (2 ml L-1) significantly reduced the numbers of galls, final population, population build- up (Pf/Pi) and nematode reduction percentage. About 1 ml of fulvic acid indicated all best treatment, and the application of both humic acid was nearly effective as Vydate (double treatment). The double application of humic acid gave the best plant growth (fresh and dry weights) in cow pea and tomato plants. All treatments reduced nitrogen content in plants (tomato and cow pea plants), but fulvic acid once or twice dose increased phosphorus content in tomato plant more than vydate. Potassium content in tomato plants was increased in vydate treatment than in the other treatments.