Traditionally, marigolds are grown to combat nematodes. But if you don't want to lose a season's worth of bed space to growing flowers (though since they attract bees are good to grow around plants that need heavy pollination) if you can ballpark identify the type of nematode you have, grow something that they don't like, or a crop that is resistant to that nematode. The last thing you want to do is feed them. There are also chemical solutions to nematodes. They are more of a problem here because we don't have winters to kill them off.
Another good strategy to dealing with soil pests is container gardening. For example if you want to grow a tomato that is susceptible to blight, grow it in a container until it is done and then transfer the container soil to a bed.
Another good strategy to dealing with soil pests is container gardening. For example if you want to grow a tomato that is susceptible to blight, grow it in a container until it is done and then transfer the container soil to a bed.