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White Mold on Plants: Identify, Prevent, and Treat Sclerotinia Fungus

White cottony mycelium of Sclerotinia sclerotiorum on plant stem causing white mold disease.

Cottony white growth on a plant stem caused by the pathogenic fungus Sclerotinia sclerotiorum, which leads to the disease known as white mold.

Image Credit:
RJymm/Wikimedia
Written By: Catherine Boeckmann Executive Digital Editor and Master Gardener

Have you spotted a soft, white fuzz creeping up your plants or vegetables—almost like cotton candy on the stems? That’s white mold, or Sclerotinia, a stubborn fungus that thrives in cool, damp gardens. It can infect beans, tomatoes, lettuce, peas, and dozens of other crops, often appearing right when plants are blooming. I’ve learned over the years that catching this disease early is key, because once it spreads, it’s hard to stop. Here’s how to identify, control, and prevent white mold before it takes over your garden beds. 

What Is White Mold (Sclerotinia)?

White mold, or Sclerotinia sclerotiorum, is a fungal disease that affects more than 360 types of plants, including beans, peas, lettuce, tomatoes, cabbage, and many flowering ornamentals. When white mold hits tomato plants, it may be called timber rot.

This fungus thrives in cool, damp conditions, usually during spring or early summer. Spores spread through the air or by water splash, infecting flowers and stems when humidity is high and air circulation is poor.

white mold growth on a cabbage stem
White mold creeping up a cabbage stem—once it starts, this fungus can spread fast in damp garden beds. Credit: Cornell

NOTE: White mold is not the same as white rot (Sclerotium cepivorum), which primarily attacks onions, garlic, and related crops. White mold spores persist in the soil. White rot spores survive mainly in onion and garlic bulbs or in infested soil.

Sclerotium cepivorum (white rot) on onion bulb
White rot on an onion bulb. This disease only affects allium species, especially onion and garlic. Credit: Steven Koike

How White Mold Spreads

White mold spores can travel by wind, water, tools, or even your hands after handling infected plants. They thrive in humid, cool conditions, often during flowering or early growth stages. The spores land on plant tissue—especially flowers—and germinate in cool, moist environments. Once this fungus takes hold, it can overwinter in soil for several years. That’s why prevention is key: once it’s in the soil, it’s tough to eliminate.

Identification

How to Identify White Mold on Plants

White mold symptoms vary by plant, but the early warning signs are often subtle. Keep an eye out for:

  • Fluffy, cottony white fungal growth on stems, blossoms, or pods.
  • Water-soaked spots on stems or leaves
  • Wilting or yellowing leaves, starting at the base
  • Black, seed-like sclerotia that form later inside stems or pods
  • Leaves or pods may rot, and stems can become brittle
Early white mold (Sclerotinia) infection showing cottony white mycelium on snap bean stems.
White mold on snap beans shows the fluffy, cotton-like mycelium of the fungus on stems and pods. This white growth is the first visible sign of the disease. Credit: Ohio State University

Tip: The white growth appears first, then black sclerotia form later. This differs from white rot, which usually affects the bases of bulbs like onions and garlic. If you notice one plant showing these symptoms, it’s best to act fast—white mold spreads easily to nearby plants.

Black sclerotia forming in white mold growth on snap bean stems.
See the black spots that look like mouse droppings on the white mold? As white mold matures, black, seed-like sclerotia form, allowing the fungus to survive in soil for years. Credit: Cornell University

Control and Prevention

How to Control and Treat White Mold

If you find infected plants, here’s what to do:

  1. As soon as you notice any diseased plants, destroy them immediately—do not compost them.
  2. If your soil is infected, remove as much of it as you can and replace it with clean soil or solarize it (cover the infected ground with clear plastic for several weeks in full sun) to prevent the spread of the disease.
  3. Avoid overhead watering—water at the soil level instead.
  4. Consider using an organic fungicide labeled for white mold (apply before flowering and repeat one week later).
  5. Rotate crops so the same type of plant isn’t grown in the same spot each year.

How to Prevent White Mold in Your Garden

An ounce of prevention really is worth a pound of cure when it comes to fungal diseases. Here’s how to keep white mold away:

  • Space plants properly for good air circulation.
  • Water early in the day so foliage dries before nightfall. Here are the best times to water your plants.
  • Keep weeds in check—they can harbor the disease.
  • Clean up all crop debris after harvest. The fungus can survive on leftover stems and leaves.
  • Mulch or use plastic barriers to reduce soil splash onto plants.
  • Rotate crops yearly, especially legumes, cabbages, and lettuce.

If you’ve struggled with white mold in the past, try planting resistant varieties or adjusting garden layout for better airflow.

White Mold on Houseplants

White mold can appear on houseplant soil or leaves if conditions are too damp. To fix it:

  • Let the top inch of soil dry out between waterings.
  • Remove any white fuzz with a paper towel and discard it.
  • Improve air circulation indoors.
  • Repot with fresh soil if needed.

White Mold vs. White Rot and Other Diseases

It’s easy to confuse white mold with white rot. Here are the key differences.

FeatureWhite Mold (Sclerotinia)White Rot (Sclerotium)
HostsBeans, peas, lettuce, cabbage, tomatoesOnions, garlic, leeks, shallots
SymptomsCottony white growth on stems/flowers; black sclerotia in pods/stemsWhite fuzzy growth at base of bulbs; bulbs rot; black sclerotia in/on bulbs
SpreadAirborne spores, soil, water splashSoilborne only; spreads via bulbs or infested soil
SeasonCool, humid spring/early summerCool, wet soil conditions; onion/garlic beds

Some gardeners can also confuse white mold with gray mold (Botrytis) or powdery mildew.

FAQ About White Mold

Q: What causes white mold?

White mold thrives in cool, damp, and poorly ventilated conditions—especially when plants are crowded or watered from above. The spores can persist in soil for several years and infect plants when moisture levels are high.

Q: How do I get rid of white mold?

Remove infected plants, solarize the soil (cover it with clear plastic for several weeks in summer), and rotate crops yearly.

Q: How is it different than white rot?

White mold attacks many vegetables; white rot attacks onions/garlic. The two diseases look similar but affect different plant families.

Q: Can white mold spread to my houseplants?

Yes, if the soil stays damp. If you see white fuzz, scrape it off, let the soil dry out, and improve air circulation. Repot with fresh soil if needed.

Q: Can I eat infected vegetables?

No, discard them. The fungus can produce toxins.

White mold can be discouraging, but with good garden hygiene, smart watering, and crop rotation, it’s possible to keep it at bay. I always remind new gardeners: even the best of us lose a plant or two to fungus—it’s part of learning how to work with nature, not against it. Keep observing your garden, and before long you’ll spot trouble before it spreads!

Plant Disease

About The Author

Catherine Boeckmann

Catherine Boeckmann

Executive Digital Editor and Master Gardener

Catherine Boeckmann is the Executive Digital Editor of Almanac.com, the digital home of The Old Farmer’s Almanac. She leads digital editorial strategy and publishing across a wide range of Almanac sub...

Read more from Catherine Boeckmann

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Comments

<span>Kathy Joyce</span> Thu, 06/27/2013 - 16:10
The flowers on both my petunia plants have polka dot-looking white spots on each bloom. They are separated from each other the length of the small patio. I did water each evening, they have drainage holes. What happened?
<span>Kathy Joyce</span> Thu, 06/27/2013 - 16:13
Thanks for answer to petunia white dots,
<span>Lad</span> Mon, 06/24/2013 - 11:23
On my sunflowers, there is a sticky white drippy looking substance between the main stem and the leaf stem. What is this and how should I treat it? And, is it contagious to the garden generally?
<a title="View user profile." href="/author/editors">The Editors</a> Tue, 06/25/2013 - 09:50
Every once in a while we don't have a clear and specific answer and this is one of those times, Lad. You do not indicate where you are but it seems that the sticky white substance may not be from the plant itself but from whiteflies or aphids. Now you wonder, what to do? If indeed this is the case, ideally, you would want to encourage "good bugs" (some wasps, predatory mites, black ladybird beetles, for example, depending on your area) into your garden to eliminate these pests rather than apply insecticides, which might destroy any good bugs that are present. A good bug welcome mat can not be put out in a day; it's often a gradual thing that can be accomplished by bringing in other plants. To have a better idea of what you're dealing with and how to eliminate it, we suggest that you contact your local agricultural extension service. They would be more familiar with specific conditions in your area. Hope this helps—Best wishes!