Garlic White Rot, Anyone?

A few newly weeded, super-cute, disease-free (knock on wood) garlic plants.

I love garlic. With a harvest of just four garlic braids last year, I decided we needed to ramp up production. In fact, I set a goal of growing a year’s supply of garlic this winter. I think we’re going to fall a bit short of the mark, but I’m pleased to report that we do have one long raised bed devoted to garlic and onions.

I’ve never known much about garlic diseases, and I’ve always had healthy alliums. This past weekend, however, I overheard talk of garlic white rot. By the fearful tenor of the gardener doing the talking, I decided this might be a disease worth looking up.

I didn’t have to look far. Sclerotium cepivorum, the fungus that causes white rot, can quickly kill garlic and onion plants. First the plant’s leaves turn yellow and die back. Then the bulb begins to rot. Apparently at this stage, it’s very easy to pull up the garlic, and you’ll find telltale white fluff on the bulb. The fluff later becomes more compact, forming black pinhead-sized sclerotia.

Pinhead-sized What? 

In laymen’s terms, sclerotia are hardened fungal bodies that allow the fungus to survive tough times. For garlic white rot, this means that the fungus can live in the ground for upwards of thirty years without food, just waiting for the next garlic or onion planting to feed on. I shudder to think of waiting thirty years to grow garlic again.

Of course you don’t have to wait that long to plant again, and there are a number of treatment methods available to farmers. According to UC Davis, however, chemical treatments are necessary in order to grow alliums once soil is infected with white rot.

I’m no expert on any of this, but what I found most sobering was the thought that I could inadvertently introduce white rot through planting infected garlic sets and then be stuck with the disease for the rest of my gardening life.

Aside from planting garlic from seed, which sounds like a pain to me, there are a number of prevention and organic management options, all boasting imperfect results. For instance, it’s possible to dip cloves in hot water before planting with the hope of killing off the fungus. If your soil is already infected, you can plant bunching onions. They’ll trigger the sclerotia to germinate, but won’t allow time for new sclerotia to form before harvest.

I guess the moral of the story for those of us lucky enough to have avoided the disease thus far is to be extremely cautious about where we get our garlic sets, or to plant from seed. Planting leftover cloves from the grocery store is probably a terrible idea, given that there’s no way of knowing the garlic’s origins, let alone the condition of the soil in which it grew.

But what about planting sets from a nursery? For the past several years, we’ve purchased sets from Common Ground, a local organic nursery. I’ve also saved and replanted my own elephant garlic, since I find the sets unpalatably spendy.

I spent a few hours this morning doing some long-overdue weeding in the allium bed. So overdue in fact, that plant excavation might be a more appropriate description. So far, thankfully, my little alliums look healthy despite their gardener’s lack of attention to the threat of white rot. Whether I’ll continue planting nursery sets without further precaution next year, I haven’t yet decided. At this point, I can’t see myself planting a year’s garlic from seed, but from what little I’ve learned of white rot, I’d hate for laziness to be my folly.

Before the excavation.

After the excavation.

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