Caption
Gray mold has compromised these Riesling grapes.
Simple tips to protect your plants from one of the most common garden fungi.
Do you ever look at your beautiful plants and see something fuzzy and gray? It might be Gray Mold (Botrytis), a common but nasty fungus that can strike your garden when you least expect it. It affects many parts of the plant: leaves, flowers, stems, and fruit. Luckily, with a few simple steps, you can identify, prevent, and treat this fungus before it spreads.
What Is Gray Mold?
Gray mold is a pesky fungal disease caused by the fungus Botrytis cinerea. It’s not picky about its host—this pathogen can go after many different garden plants, from flowers to vegetables. Once it shows up, it spreads fast, riding along on the wind, splashing water, garden tools, or even on your hands.
A quick note so the terms don’t get confusing:
- The fungus itself is Botrytis cinerea.
- The disease we see on plants is called gray mold.
Commonly Affected Plant Parts:
- Leaves: Small brown or water-soaked spots that may develop fuzzy gray mold
- Flowers: Wilting, browning, or fuzzy coating on petals
- Stems: Gray mold can rot stems at the base or nodes
- Fruits: Soft spots, rotting, and gray spore growth on tomatoes, strawberries, grapes, and other fruits
Why It Happens:
This develops when plants and their environment create the perfect storm for infection. This pathogen thrives in cool, damp, and stagnant conditions, especially when plants are stressed or damaged.
- High humidity keeps leaves and stems moist, which allows fungal spores to germinate and spread.
- Poor airflow prevents that moisture from evaporating, leaving a lingering damp layer on foliage and flowers.
- Excessive watering—or water that splashes onto leaves—further increases surface moisture and can even spread spores from one plant part to another.
- Decaying plant material (fallen leaves, old blossoms, pruned stems) acts as both food and a breeding ground, where the fungus produces more spores ready to infect healthy tissue.
Together, these factors weaken plants and make them vulnerable to infection. Even healthy plants can fall victim if conditions stay wet and stagnant long enough, since Botrytis is an opportunistic fungus that attacks wherever there’s soft, damaged, or aging tissue.
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Identification
How Gray Mold Spreads
Early recognition is key to stopping Gray Mold early. Here’s how it progresses:
- Generally, small spots that appear water-soaked will form on the leaves. These might appear white at first.
- These spots will then change color from gray to brown, eventually covering most of the leaf. The brown coloration is what often causes people to confuse gray mold with brown mold.
- Under really humid conditions, grayish webbing may appear on the leaves. This webbing contains structures that contain fuzzy spores. Spores become active and are released with no activity at all.
- Petals, stems, and buds can also become infected.
- Eventually, all of the infected parts of the plant will be covered by a fuzzy gray growth .
Symptoms to Watch For
- Gray, fuzzy mold on leaves, stems, flowers, or fruit
- Wilting, browning, or softening of plant tissue
- Rapid spread under cool, humid conditions
- Small spots that enlarge quickly if untreated
Tip: Check plants regularly, especially during damp weather or in areas with dense foliage.
Photo Credit: Francesca Peduto Hand, The Ohio State University.
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Comments
Black specs might be "frass"...caterpillar poop. You may have a worm eating your plants. Blast the leaves with insecticide spray.
Are the hydrangea leaves turning brown around the edges? Usually, this is a moisture issue. Sometimes, the plant can be root-bound, too.
Gently dig the plants early in the morning to check for both conditions. If needed, lightly loosen the roots with your hand. You can also soak the root ball in water until it's moistened through. Make sure you maintain uniform moisture for your hydrangeas.
Location can also be an issue. If they're getting sun burnt, they'd do better with light shade.
It sounds like your plant may be getting too much sun. Move it to a cooler spot in the house; be sure it is not close to heat vents or on top of the television.
It's probably powdery mildew from humid conditions. It isn't pretty but it won't hurt the peony this late in the year. Cut it back in the fall and dispose of the leaves. Make sure your peony has good air circulation next year. It may be a good idea to move it away from the hydrangea. Go to our peony page for more information. www.almanac.com/plant/peonies
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It appears that the problem might be powdery mildew. To find out how to prevent and control this fungal disease, go to our powdery mildew page.