Hi Dave –
I have been told numerous times that Beneficial Nematodes will NOT work on Root Knot Nematodes. In fact the University of Florida states:
“Currently, no predators are commercially available for augmentative releases for nematode control in vegetable production systems.”
So, the question is; how do you control harmful “root-feeding” nematodes organically? Chemical nematacides are available, but very expensive, extremely toxic and not approved for organic use. I believe your best bet for getting rid of root knot nematodes in the garden is to combine several least-toxic strategies, which include the following:
• Grow resistant varieties. Look for an “N” on the seed packet which indicates nematode resistant.
• Avoid moving infected soil to other parts of your garden. Nematodes do not travel far, but can be spread with tillers and hand tools.
• Rotate garden crops with plants that are known to reduce nematode numbers. Broccoli and cauliflower have been mentioned as good rotation crops.
• Soil Solarization — heating the soil with clear plastic prior to planting will reduce or eliminate many harmful organisms including nematodes.
• Build your soil with good organic soil amendments. Shellfish fertilizer (https://www.planetnatural.com/product/shellfish-fertilizer-50-lb/) contains chitin which encourages the growth of organisms that inhibit harmful pest nematodes.
Hope this helps!