Neck rot in garlic is caused by Botrytis fungi that get into the neck tissue around harvest and cure time, and UC IPM’s Pest Management Guidelines for Onion and Garlic (UC ANR Publication 3453) tie the fungus’s activity in soil to a temperature window of 50 to 75°F. The damage rarely shows at digging. It shows up weeks later as grey fuzzy growth and hard black flecks between the scales, once bulbs are already braided or bagged. Check every neck for firmness before you commit a batch to storage, because a soft neck now becomes a collapsed, mushy bulb within a month.
What you are looking at
In the field, plants carrying a heavy infection look stunted next to their neighbors, with the outer leaves dying back from the tip. The tissue at the base of the leaves and neck turns water-soaked at first, a dull grey-green that looks bruised rather than diseased, then dries out to a papery, straw-colored necrotic patch. This is easy to miss at harvest because garlic naturally yellows and dies back as it matures, and a grower digging a full bed has no reason to inspect every neck closely.
The disease declares itself properly in storage. Cut into a neck that has gone soft and you will find grey, fuzzy sporulating growth spreading between the scales, sometimes dusty enough to puff when disturbed. Within that grey mat sit small, hard, black bodies called sclerotia, often no bigger than a match head, irregular in shape rather than round. These sclerotia are the fungus’s survival structures, and their presence is the clearest confirmation you are dealing with neck rot rather than ordinary storage shrinkage. A bulb like this feels soft or spongy when you squeeze the neck, well before any smell develops.
Where to look first
- Squeeze every neck at curing, not just the ones that look wrinkled
- Cut open any bulb that feels soft at the neck, do not just discard it unopened
- Check between the outer scales for grey fuzz, not just the surface
- Note that symptoms often appear two to four weeks into storage, so a clean-looking harvest day tells you very little
What it is not
Most yellowing garlic is not diseased at all. Garlic naturally dies back as bulbs mature, and uneven watering, nitrogen shortage, or plain heat stress will all yellow leaves from the tip down in a way that looks alarming but resolves on its own or simply signals it is close to harvest time. The detail that separates ordinary dieback from a real problem is timing and pattern: dieback that matches the rest of the bed and arrives near expected harvest is normal, while stunting and collapse that hits scattered plants earlier than their neighbors deserves a closer look.
Two other garlic problems get confused with neck rot because they also cause stunting or off-color foliage, but each has one detail that rules out the others.
| Problem | Where it shows first | Distinguishing detail |
|---|---|---|
| Neck rot (Botrytis) | Neck and outer leaf base, then storage | Grey fuzzy growth and black sclerotia between scales |
| Pink root | Roots | Roots turn pink to red and shrivel, foliage stunts but bulb tissue stays firm |
| Garlic mosaic virus | Leaves, from emergence | Yellow or light green streaking along the leaf blade, bulbs shrink over generations rather than rotting |
| Natural dieback | Whole planting, evenly | Matches expected harvest timing, no soft tissue or fuzz on cutting |
If your garlic is yellowing evenly across the bed as harvest approaches, that is very likely just maturity, not disease. Reserve suspicion for plants that lag behind their neighbors or bulbs that go soft at the neck after they are already in storage.
Where it comes from and when it strikes
Botrytis is a soil-borne fungus that also survives on old crop debris and on infected seed cloves, which is how it most often enters a garden that has never grown garlic before. Once established, it produces sclerotia that sit in the soil between plantings and germinate again when conditions suit them, which is part of why a single bad season can leave a bed compromised for years afterward.
UC IPM’s guidelines put the fungus’s active range at 50 to 75°F, and that figure is a soil temperature, not an air temperature reading off a weather app. Soil in a mulched or shaded bed can sit well below the air temperature on a warm afternoon, and the reverse is true on bare, sun-baked ground, so a thermometer pushed a few inches into the row is the only honest way to know where your soil actually sits relative to that range. Within that window, and especially where the soil stays damp, the fungus grows readily and infects through wounds, through the cut neck left by trimming leaves too early, or through tissue softened by late-season overwatering.
Infection often begins in the last weeks before harvest, when necks are still green and pliable and easily bruised by wind, foot traffic, or careless pulling. It does not need the whole plant to be weak. A single nick at the base of a leaf is enough of an entry point once soil temperatures and moisture are in its favor. This is why the disease so often seems to appear out of nowhere in storage: the infection happened in the field, quietly, and simply needed the weeks after harvest to become visible.
What to do about it now
There is no cure once a bulb has visible grey growth or sclerotia between the scales. Fungicides will not reverse tissue that has already broken down, and a bulb that is soft at the neck will not firm back up in storage no matter how it is handled from that point on. The only useful response is to find infected bulbs early and pull them out of the batch before the fungus spreads spores onto sound neighbors sharing the same braid, crate, or mesh bag.
Sorting and handling
- Cull any bulb with a soft neck or visible grey fuzz as soon as you find it
- Move healthy-looking bulbs from the same bin to fresh, dry storage rather than leaving them in contact with a diseased one
- Handle culled bulbs last, or wash your hands after, since spores transfer easily on damp skin and tools
Do not compost affected bulbs or the trimmed tops from a bed you suspect had neck rot. Home compost piles rarely sustain the heat needed to kill sclerotia reliably, and tossing infected material into the pile is a straightforward way to seed the fungus into every bed that pile eventually feeds. Bag and discard it with household trash instead, and if you saved cloves from that harvest for replanting, treat them as suspect rather than as free seed stock for next season. This is one more reason a solid garlic disease routine starts with knowing what came out of the ground before you decide what goes back into it.
Keeping it out of your garden
Prevention for neck rot happens almost entirely at curing and in how the crop is handled in its last weeks, not with a spray program. UC IPM’s guidance lists several controls, and the ones within easy reach of a home garden are the ones worth focusing on.
What actually helps
- Cure thoroughly. Harvest at maturity and let necks dry completely before bundling or bagging, since a green, pliable neck is exactly the tissue the fungus infects most easily.
- Cut back late nitrogen. Nitrogen applied late in the season keeps plants soft and leafy right when you want necks toughening up instead.
- Ease off irrigation as harvest nears. Reducing water in the final weeks lets the neck dry down naturally and firms the tissue against bruising.
- Handle bulbs gently. Bruised tissue anywhere on the bulb is an entry point, so pull rather than yank, and set bulbs down rather than dropping them into a bucket.
- Store cold. UC IPM’s guidance sets a storage target of 41°F or below, which slows any low-level infection that made it through curing undetected.
Behind all of this sits the fact that sclerotia survive in soil for extended periods, according to UC IPM. That single fact changes how you should treat seed stock: cloves saved from a bed that had any neck rot the previous year carry real risk, and planting garlic back into the same ground year after year lets any sclerotia that formed simply wait for the next crop. Rotating garlic and other alliums to a different bed, and starting new plantings from cloves you know were clean at harvest, does more for next year’s storage life than any treatment applied once symptoms appear. None of the more aggressive commercial measures, deep plowing to bury debris, soil fumigation, calendar-based fungicide programs, make sense at garden scale, and a home grower gets far more from clean seed and a dry cure than from trying to replicate a field operation in a raised bed.
Common questions
Can I still eat garlic that has a little neck rot?
Cut away the affected bulb and use only unaffected cloves promptly, since the rot spreads inward from the neck and infected cloves will taste off and soften further even after cooking. Do not save any clove from that bulb for replanting.
Will neck rot spread from one bulb to the rest of my braid?
It can, since spores from the grey sporulating growth land readily on neighboring tissue in a warm, humid storage space. Pull any suspect bulb out of the braid or bin as soon as you spot it rather than waiting to see if it worsens.
Is it safe to Plant Garlic in the same bed next year?
It is riskier if that bed had any neck rot, because sclerotia persist in the soil for extended periods according to UC IPM. Rotating garlic to a different part of the garden for a few seasons gives any surviving sclerotia less to infect.
My garlic necks are still green at what I thought was harvest time. Should I wait?
Green, pliable necks are more vulnerable to infection, so pulling too early and forcing a fast dry-down is not a fix. Local harvest timing varies by climate and cultivar, so check your state extension service or county office for the maturity signs typical in your area before deciding.