what caused my garlic to rot? rotation, rotation, rotation

I've been thinking about why half of my garlic crop rotted this year.

In early spring, my garlic plants yellowed and curled and then died. This started mostly in one area of the bed and then gradually other plants curled and died more slowly. Some just stopped growing looking like a small plant, but when pulled, the bulb was rotten.

Once I saw the plants rotting, I worried that I planted where onions had been last year and maybe garlic the prior. This is my list for crops the bed the garlic was in.

2009: tomatoes, peppers
2010: beans, dill
2011: squash
2012: garlic
2013: roots, including onions
2014: squash
2015: garlic

So next I looked into garlic rot information online. I looked at a Cornell Plant Clinic factsheet on garlic diseases. There are several different types of garlic rot. I'm not sure which I had, but the ways to address them all are the same, so I'm not going to worry about an ID.

The Cornell sheet says:

... as with any crop, it is important to plant clean healthy seed. For most of the mentioned diseases (Basal Rot, White Rot, Downy Mildew and Nematode infestation), once the pathogen is established in a field, rotation away from Allium spp. for several years is an essential management tool.

It looks to me like I didn't rotate well because onions are also an Allium species. I think they snuck in there are ruined my 3 year rotation. Darn.

Well, next year I'll have clean fresh garlic seed and I'll see what I can do to avoid this bed for a long time.