HOST STATUS AND AMENDMENT EFFECTS OF COWPEA ON MELOIDOGYNE INCOGNITA IN VEGETABLE CROPPING SYSTEMS

Abstract

A field experiment was conducted to study the mode of action of cowpea (Vigna unguiculata) on plant-parasitic nematode suppression, and to differentiate the nematode suppressive effect from the green manure effect performed by cowpea. The experiment was a 3×3 split-plot design in which the main plots were summer planting of Meloidogyne incognita resistant ('Iron Clay') and susceptible ('White Acre') cowpea, and fallow. The three subplots received biomass of 'White Acre' cowpea or 'Iron Clay' cowpea or no biomass. Planting of cowpea (regardless of cultivar) resulted in phytotoxicity to 'Purple Top' turnip (Brassica rapa) when planted immediately after the cowpea cover crop. Planting of 'Iron Clay' cowpea suppressed M. incognita population densities due to poor host effect rather than from any allelopathic effect from crop residue amendments. However, this nematode suppression was only significant in crops that were very susceptible to M. incognita such as bush bean (Phaseolus vulgaris) and lima bean (P. lunatus). Green manure (crop fertility) effect from growing cowpea was negligible on leguminous cash crops. However, the yield of turnip, a non-leguminous crop, was higher when plots were previously 'Iron Clay' cowpea followed by the cover crop amendment as compared to plots that were fallow without cowpea amendment.