I can't find the memory stick the scans are on (I moved), and the ARS annuals are boxed in the garage, but in the seventies or eighties, there were at least two articles in the American Rose Annuals about the use of ground pine bark cleaning root knot nematodes from the soil. It was used both as an amendment, mixed in the soil as well as a mulch. Previously infected soils and plants were found to be "cleaned" of the infestation simply due to the cleansing action of the pine bark. You might consider using it if it's locally available in your area. You might also search this forum for the scans as I am sure I have posted them within the past two years when the nematode question was raised previously. Good luck.

Personally I have given up doing anything to the soil to control these nematodes. Whatever I have done works for a while, but the nematodes come back. Any type of organic material discourages them, so worm castings and the soil drench described above should have some effect. However, I think the effects will be rather short-lived. Maybe if you have vegetables or something that you harvest in one season it will help a lot. I try to plant perennials and there has only been a few things that have worked for me. First is to buy plants that aren't bothered by these nematodes. Most azaleas and camellias, for example, aren't bothered by them, nor are most trees. On the other hand roses and gardenias need to be grown on grafted rootstocks--although there are some roses (Louis Philippe sp?) that are resistant. The second thing that works for me is to put the plants in pots, use potting soil or amended soil and then place the pots on some type of cement or concrete. The nematodes don't like concrete. If you put the pot on the ground eventually the nematodes will reach the roots. The nematodes love sandy soils. Some people who live in areas with little sand aren't bothered by them as much, however, most of Florida sits on top of sand, so most of us need to be concerned with root knot nematodes.

I removed the chard. For now I think I'll dig in plenty of organic matter, and plant mustards and rapeseed in the area, and dig them in before they flower. I'll probably eat some of the mustard greens along the way. Not too much of a sacrifice as I was probably going to plant some mustard greens there anyway.

I haven't used them for that myself, but Beneficial nematodes are known to combat root knot nematodes. I have used them for various grubs in the lawn and in pots and they worked very well.