Root-Knot Nematode in Strawberry

Do you know how to diagnose root-knot nematode in strawberry?

We recently came across a rare occurrence of root-knot nematodes in two samples submitted to the Strawberry Center’s Disease Diagnostic service. The samples were both from the Santa Maria district and were both positive for root-knot nematodes (Meloidogyne spp.). The species most commonly associated with damage in California strawberries is the northern root-knot nematode, M. hapla. We are still working on identifying the species in the current samples.

If you suspect root-knot nematodes look for mild root galling and stubby roots (Fig. 1 and 2). Using a 14X or 20X handlens you’ll be able to find some gravid females protruding from the root surface (Fig. 3). If you find these symptoms, please submit a sample to Cal Poly Strawberry Center’s Disease Diagnostic Service to confirm the diagnosis.

Below are several photographs showing what to look for.

Figure 1. Stubby root symptom in strawberry. (photo by S. Hewavitharana)
Figure 2. A close-up of a stubby strawberry root. (photo by S. Hewavitharana)
Figure 3. Root-knot nematode gravid female containing eggs. (photo by S. Hewavitharana)

The female nematodes are barely visible to the naked eye and can be seen using a 14X or 20X handlens. The female nematodes become enlarged and produce many eggs (Fig. 3) which you can see with further magnification. A gravid female is about 0.7 mm long, much smaller than a two-spotted spider mite (2-3 mm). When the environment is favorable, a single female may produce 1,000 eggs (Fig. 4).

Figure 4. Root-knot nematode eggs.
(photo by S. Hewavitharana)

After conducting a soil nematode extraction, male and juvenile nematodes (Fig. 5) can be observed.

Figure 5. Juvenile Meloidogyne sp. nematode. (photo by S. Hewavitharana)