Effect of cover crops and cultural treatments on plant parasitic nematode density, fungal root disease severity and yield in white clover

Abstract

Maize (Zea mays), sorghum (Sorghum bicolor), rapeseed (Brassica napus) and molasses grass (Melinis minutiflora) were tested for their ability to host clover root-knot nematodeMeloidogyne trifoliophila in a glasshouse pot experiment and were found to be a poor hosts. A second experiment determined the value of these plants as soil amendments in reducing nematode numbers or improving white clover (Trifolium repens) growth. The effects of these crops together with a range of cultural treatments were also evaluated in a field experiment at Wollongbar Agricultural Institute, New South Wales, Australia, for their impact on nematode population and root rot disease severity. A chopped shoot amendment of sorghum was effective (P<0.05) in reducing the number of root galls and eggs in white clover roots and improving plant growth in the pot test. Overall, cover crop treatments, in particular molasses grass and maize, reduced (P<0.01) field densities of Heterodera trifolii but the population densities recovered quickly after re-establishment of white clover pasture. Dry matter yields were improved only up to 11 weeks after clover establishment. Although cover crops showed potential for improving yield and in reducing the population of certain nematodes, removal of white clover pasture for 5 months as a management practice does not appear to be useful in overcoming root and stolon rot diseases of white clover in this subtropical climate.