The use of olive mill wastes for the control of root-knot nematodes

The suppressive effect of olive mill wastes was tested in a field experiment in sandy soil, infested by Meloidogyne incognita, in the Province of Lecce, southern Italy. The field was subdivided in 12 m2 plots distributed at random in four blocks. Treatment consisted of different dosages (10, 20 and 40 t/ha) of two composts prepared with either exhausted or fresh olive pomace or raw extraction sewage at rate of 40 or 80 m3/ha. There were four untreated control plots and four plots on which the granular 5% formulation of fenamiphos had been broadcast incorporated into the soil at the rate of 300 Kg/ha, one week before planting the tomato cv. Tondino di Zagaria. All treatments statistically increased tomato yields with respect to the control. Conversely, the root gall index, assessed according to a scale from 0 (no gall at all) to 5 (root system of reduced size and deformed by large galls), was significantly reduced in all treated plots. Also soil populations of the root-knot nematode declined, significantly compared to the control, except in the soil treated with the lowest doses of raw sewage or exhausted pomace compost.