There are many beneficial nematodes in agricultural soil, however some nematodes are plant parasitic. When plant parasitic nematodes are present in high numbers in soil, they can cause significant yield losses to horticultural crops. The extent of loss depends on the crop, nematode species and soil populations.

The most destructive and common plant parasitic nematodes in Ontario fruit crops are root-lesion (Pratylenchus penetrans) and northern root-knot (Meloidogyne hapla). The northern root-knot nematode is becoming more prevalent. The pin (Paratylenchus sp.) and dagger (Xiphinema sp.) nematodes occasionally cause yield losses to some fruit crops in isolated fields. The dagger nematode is mainly a virus vector on grape, raspberry and apple.

Generally, symptoms of nematode injury include:

  • uneven plant growth
  • poor plant establishment
  • plants weakening over time
  • poor root growth
  • knots or galls on roots
  • excessive branching of roots, hairy root symptoms

Root-lesion nematodes can be a major cause of orchard replant failures. They can also cause a decline in vigour of existing peach and cherry orchards. These nematodes cause small brown lesions on the white lateral roots and kill the fine feeder roots. When lesions merge, the entire root system appears discoloured. Root lesions are frequently invaded by other pathogens which can cause root rot. Severely affected trees may lose all feeder roots. Young replant trees may die. Existing trees lack uniformity.