Nematodes of grasses and weeds

Abstract

Numerous grass species are used as pasture and cover crops in crop rotation systems in South Africa. A wide range of weed species are also present in local cropping systems and adversely affect crop production. The identification of the economically important nematode pests that are associated with both grasses and weeds is presented. The presence of the seed- and leaf-gall nematode Subanguina wevelli in seeds of Eragrostis curvula is, for example, a matter of great economic concern to the local grass seed industry. Methods to eliminate seed- and leaf-gall nematodes from consignments of grass seed for export, including the use of sieving and flotation, have been investigated, but were ineffective. Ryegrass toxicity, resulting from the association of Anguina funesta with a coryneform bacterium (Clavibacter sp.) and A. agrostis with the bacterium Clavibacter toxicus is also described. Every year, cattle and sheep die from ryegrass toxicity. Concerning weeds, an extensive nematode survey was done in the fields of local smallholding farmers and showed the association of a wide range of plant-parasitic nematodes with 38 weed species. The predominant plant-parasitic nematode species identified were Meloidogyne hapla, Meloidogyne incognita, Meloidogyne javanica, Pratylenchus zeae, Helicotylenchus dihystera, and Rotylenchus unisexus. Both survey and host suitability assays showed that Tagetes minuta, reported and perceived to be a poor host of Meloidogyne spp., have the potential to serve as a good host for the economically important root-knot nematode species M. incognita and M. javanica