I'm pretty sure I have garlic nematode. More than half the crop is lost due to stunted, rootless, soft, stinky bulbs. I pulled the whole crop and can salvage some. How can I treat the soil?? Cover crop? Solarization? Of course I'll buy all new seed and plant in whole new spot. I want to get my soil back to clean and healthy.
I can't tell from your pictures if nematodes are the problem, or rot caused by other issues. The cure for all is to remove all remaining vegetation and not plant anything in the onion family or pea, parsley, celery, and salsify, which are alternative hosts for nematodes, in the area for four years. You could solarize with clear plastic, but it isn't necessary as long as you keep all of these away long enough for the problem to resolve itself. You can plant any other crops there while you are waiting them out.
See http://www.extension.umn.edu/garden/fruit-vegetable/growing-garlic-in-minnesota/index.html#botrytis and https://extension.umd.edu//sites/extension.umd.edu/files/_docs/articles/GarlicProblems_5-9-13.pdf for more information.