Like everyone I would like to avoid Nematodes. I’ve read hot water dips get rid of Nematodes prior to planting but who knows about the best way? My ground does not have Nematodes of any kind at this time. I’ve read they are devastating to garlic crops. http://ipm.ucanr.edu/PMG/r584200111.html. I got black rot once on a grape I ordered from a reputable nursery and it took years to eradicate BR. Never hurts to be as careful as possible right? This guide looks interesting which discusses vegetable production http://extension.psu.edu/publications/agrs-028
Update
The bulbs can actually be tested. The hot water method is no longer recommended http://www.extension.umn.edu/garden/yard-garden/vegetables/stem-and-bulb-nematode-in-garlic/