You might be able to. There are many nematode species and they don't all affect the same thing.

Damage to onion and garlic has been observed by nematodes, but results have been mixed with some tests showing little to no damage and others showing major damage/stunting.

About all you can do is take a soil sample and send it to a lab for analysis to identify what nematode you have as a predictor of whether it will affect garlic. I don't know what this analysis costs, you might check with your extension agency to see if they have any info or if they do this analysis or simply if they know what crops are damaged by your area's nematode population.

Thanks, I'll check with extension.

~Thalia