Nematodes are microscopic roundworms. Some species have become parasitic pests of grapevines in Australia. Although they are difficult to detect, routine monitoring and careful consideration of vineyard practices- especially when planting new vines- can help reduce yield losses. Nematode infestation is verified by analysis of soil samples by a specialist laboratory. The risk of yield loss from nematodes is determined by the number of nematodes found in a soil sample of a given size.
Root-knot and other nematodes cost the industry $14 million per year, with losses varying across zones according to the cost of replanting with resistant rootstocks as well as the yield loss.
In addition to causing crop losses directly, plant-parasitic nematodes can act indirectly as virus vectors and may combine with other nematode species or fungal pathogens to exacerbate root malfunction. Badly infected vines will show poor vigour, have stunted growth and yield poorly.
The following nematodes are thought to be the most important in Australian vineyards:
- Root-knot nematode (Meloidogyne spp.)
- Dagger nematode (Xiphinema spp.)
- Citrus nematode (Tylenchulus semipenetrans)
- Root-lesion nematode (Pratylenchus spp.)
- Ring nematode (Criconemella xenoplax)
Nematode infestations can be managed in several ways.
- Resistant rootstocks can be used to help protect vines from some species of nematodes, particularly root-knot nematode.
- Chemicals effective against nematodes (nematicides) which are registered for use in viticulture are limited. Application should be concentrated in the areas in the vineyard where nematode populations are highest – this is usually along the vine rows, rather than in the inter-row strip.
- Promoting well-structured soils rich in organic matter will lead to a diverse soil ecology which might allow for the natural suppression of a range of pest organisms including nematodes.
- Biological control agents may provide some natural suppression in vineyards.
- The growth of resistant species in the mid-row may provide a mechanism for constraining nematode populations.