Nematodes are very small. If you can actually see these critters, and this is just a guess, but you might compare to onion maggot, Hylemya antiqua. More common on onions and shallots...

hortster

Thank you , horster. Yes, I can see them, so I will read up on onion maggots.

If it makes you feel better, I have never seen so many onion root maggots in garlic -- usually it's more like two heads out of a hundred, or none. This year two out of five heads of small hardnecks were ruined. These grew near one another. It is possible that there was a "lens" of damage when flies laid eggs in a small area. Some silverskins in another bed had zero damage. Any opionions on whether it was location or variety that protected the silverskins?

In the link below, you can click to enlarge the photo with the root maggots in it.

Here is a link that might be useful: photo of onion root maggots on garlic

Planatus -- thank you for the photo (who else but a gardener would be thrilled to receive a photo entitled "onion root maggots on garlic" ? :) )

Yes, that's the culprit. And I guess it was a bad year for them. At least it's not a disease that requires sterilization of tools, etc.

Thanks for the info!

I had these maggots in many of my garlic cloves this year. They were harvested from a plot that hadn't been tilled as deeply as I would have liked. Winter heaved the cloves half way out of the ground. It seems like having the top part of the clove exposed was what caused the flies to find the garlic and lay their eggs on it. Any other opinions on that?

Mine were planted nice and deep, but the prolonged wetness probably caused some rotting tissues that attracted the flies.

This year's crop went into a bed that hasn't had onions in five years. Still, I planted more softnecks and fewer hardnecks because the hardnecks had more trouble last year with root maggots and fusarium. We dried the cloves from heads with issues, but I still had plenty of clean ones for planting, and more that are holding up well in storage.

It's true it's not a disease.

But because those critters are in the soil, you must rotate all alliums out of the area for 3 or 4 years.