Nematodes

Nematodes are tiny (0.5-6mm long), worm-like creatures with needle-like mouthparts, which they use to puncture and feed from plant cells. Apart from the direct damage they cause, some species transmit viruses that debilitate the plants. Pest nematodes can be divided into two groups: those that live in the soil and feed on roots and those that are free-living and feed on aerial parts of the plant. Species of Longidorus and Xiphinema are relatively large nematodes (4-5mm long) that live in the soil. They are particularly important as vectors of various viruses, though heavy infestations of Xiphinema, the dagger nematode, can cause severe stunting and even plant death. Pratylenchus penetrans is an internal root parasite of various plants, including strawberry and raspberry. Severely infested plants show considerable stunting of roots and aerial parts, with necrotic lesions on the roots.
The stem nematode, Ditylenchus dipsaci, has a wide range of host plants. On strawberry, it lives within the plant and can invade runners while they are still closely attached to the mother plant. Young plants may also become infested from the soil, where the nematodes can survive for several years in the absence of host plants. Leaves become puckered and brittle, while stems become thickened and stunted. The leaf nematodes, Aphelenchoides spp., feed externally on young tissue within the crowns, growing points and runner buds.

Upper surface of the mid-vein of developing leaves and are most numerous in spring. A mass of them can resemble cotton wool when viewed under a microscope or strong lens. Attacked leaves become puckered and distorted, while severe infestations may cause the death of developing flower clusters and can even kill the main crown.

Cultural Management and Prevention

Unfortunately, there are no organically permitted chemical treatments for nematodes or biological controls available and little can be done to treat the site once infested. Thus, it is best to use cultural methods, such as the use of clean, certified planting material, to avoid nematode problems from the outset. The land should be checked for the presence of nematodes before planting.

Stem nematodes and leaf nematodes in infested runners may be killed by a pre-planting hot water treatment. This involves immersion of the runners for seven to ten minutes in water at 46°C, but great care is needed to avoid damaging the plants. Research in Germany and the Netherlands has indicated that planting Tagetes patula can result in a decrease in numbers of Pratylenchus in the soil..