Here’s What It Means If You See Powdery Mildew on Your Plants
Updated: Aug. 22, 2023
Getting rid of powdery mildew on plants is easier than you may think.
Gardening is full of rewards. But sometimes, regardless of whether you’re a novice or a pro, you’ll come across issues in the landscape. Powdery mildew on plants—a white fuzz or powder that usually appears on leaves and sometimes on the stem, flowers, or fruit—is a common ailment. “The upper leaf surfaces will have a powdery white-gray mildew growing on [them] that is relatively easy to wipe away with a finger,” says Sam Schmitz, a horticulturist with Ball Horticultural Company. Although powdery mildew usually occurs on the upper leaf surfaces, the whole plant can be affected.
“Powdery mildew is actually an umbrella term for a wide range of fungi that cause similar symptoms, such as fuzzy powder on leaves,” says Jessie Liebenguth, a horticulturist with Reiman Gardens at Iowa State University. “Because there are multiple fungi that cause powdery mildew, nearly all plants can be affected.”
But don’t get too concerned about white fuzz on plants or finding white fungus balls in soil. When caught early, these fungi-based diseases are easy to stop. As with other gardening quandaries—like what it means when you see brown tips on leaves or how to revive a dead plant—there are tips and tricks that’ll convince everyone your thumb is a healthy shade of green. Of course, sometimes all it takes is knowing the conditions your indoor plants need, choosing low-light houseplants, or opting for hard-to-kill houseplants.
What is powdery mildew?
Powdery mildew is a fungal disease that can go unnoticed until the environment is just right. “The spores that cause powdery mildew can be present even if the plant isn’t showing signs,” explains Lindsay Pangborn, a gardening expert with Bloomscape. “When conditions are right, they’ll start to show.” Spores can be carried by the wind, water, and even insects.
So, what’s the optimal environment for growing white mold on plants? “Shade, poor air circulation, high humidity, and moderate temperatures are favorable conditions for powdery mildew to develop,” explains Liebenguth.
In an ideal environment, white powder on plants will flourish quickly. “Powdery mildew tends to thrive in areas of poor air movement that have high humidity during the evening hours and are dry a bit during the day, in a moderate temperature range, usually between 60 and 85 degrees,” says Schmitz.
While all plants can develop powdery mildew, some are more susceptible than others. And there are plant cultivars bred to resist powdery mildew. Though you can certainly buy plants online, it’s worth purchasing from a local garden center or nursery so you can inquire about a plant’s risk. The list below will give you a good idea of the plants most likely to acquire the fungal disease.
Vegetables most likely to develop powdery mildew
- Beans
- Cucumbers
- Peas
- Peppers
- Tomatoes
- Winter squash
- Summer squash, such as zucchini
Flowers most likely to develop powdery mildew
- Bee balm
- Black-eyed Susans
- Chrysanthemums
- Dahlias
- Roses
- Peonies
- Tickseed
- Zinnias
What are signs of powdery mildew on your plants?
Powdery mildew is obvious when it begins appearing on the leaves—it’ll look like white dust or white powder. “Powdery mildew is usually seen on the broadest sections of the plants, starting out as small, white, circular spots or discoloration on the plant’s leaves,” explains Pangborn.
As it spreads, you’ll notice changes in the plant. “In its more developed stages, it will completely cover the leaf in a white or gray cast, and the leaf itself will begin to turn brown,” says Pangborn.
Once you see powdery mildew on plants, take steps to halt the fungal growth. If you don’t, the disease can take over and alter the leaves’ ability to take in sunlight. “It harms the plants by shading the leaf surfaces and preventing them from being able to photosynthesize,” says Schmitz. “These leaves can start to become a drain on the plant’s resources rather than contributing to the plant’s overall health.”
Can powdery mildew spread to other plants?
Powdery mildew can spread to the same type or variety of a plant. So if you have several zucchini plants growing in the garden and one has powdery mildew, it’s highly probable that the other zucchini plants will be affected in a short time.
But if you have other plants—flowers or vegetables like peas, for instance—growing in the vicinity, the fungi won’t spread to them. “Since powdery mildew cannot spread between different plants, it likely won’t take over your entire garden unless you have a monoculture,” says Liebenguth.
How do you get rid of powdery mildew?
There are different ways to minimize and eliminate powdery mildew on plants. The sooner you spot the white powder and take action, the easier it will be to get it under control. “The earlier the infection is treated, the better the chances of recovery,” says Pangborn.
Finding white fuzz on plants is similar to uncovering mold on houseplant soil—knowing what to do makes tackling these garden issues a lot easier. As soon as you see powdery mildew on your plants, take the actions below.
Prune the plant
“Pruning off dead leaves and stems, removing them immediately so the spores don’t further spread, is the best first step,” says Pangborn. This will improve airflow, though you may want to take additional steps to boost air circulation.
And keep this tip from Pangborn in mind as you prune: Disinfect your gardening tools to avoid spreading the spores to other plants.
Wash with a dish soap solution
Schmitz offers this genius gardening tip: Once you provide more airflow to the plants, wash the surface of the leaves with a mixture of water and mild dish soap to get rid of the pathogen as best you can.
Use a natural solution
You’d think chemical-based methods would eliminate powdery mildew on plants, but they’re more of a preventative than a treatment. “Most fungicides are preventative rather than curative, so by the time powdery mildew symptoms appear, it will be ineffective to apply a fungicide,” says Liebenguth.
Thankfully, there are nontoxic options for tackling powdery mildew on plants. “Natural remedies for powdery mildew include a baking soda or potassium bicarbonate solution, a neem or horticultural oil application, or removing infected parts of plants from the garden,” says Liebenguth.
Remove infected leaves and plant parts
When removing parts of a plant that has powdery mildew, it’s essential that you don’t toss them in the compost bin, as this can further spread the fungi. “Composting will not kill the pathogens,” says Liebenguth. As Pangborn explains, the spores can survive the composting process, leading to issues when the compost is used in the garden.
So, what’s the best way to remove infected leaves? “Burning infected leaves and stems, if possible, or bagging and discarding them,” says Pangborn. And while you’re getting rid of plant parts properly, make sure to sanitize any tools that have come in contact with powdery mildew.
How can you prevent powdery mildew?
There’s no foolproof way to completely prevent powdery mildew on plants. A good starting point? Consider the needs of each plant, including how much space each varietal needs to grow. Then be sure you’re not creating a welcoming environment for fungi while gardening. “Try not to get the leaves wet when watering plants, and encourage airflow by not placing plants too close together,” says Pangborn.
If your garden is filled with the plants most likely to develop powdery mildew, you may want to take extra steps. “The homeowner may consider applying fungicides preventatively if they have susceptible plants in their yard,” Liebenguth says. “Active ingredients include chlorothalonil or sulfur.”
When powdery mildew does appear, it’s important to properly eliminate the affected plants. “If infected leaves and stems are removed and properly disposed of, there’s a good chance those powdery mildew spores won’t make a comeback the following year,” says Pangborn. “However, spores can blow in from anywhere, so unfortunately there’s no surefire way to avoid it from year to year.”
If all that sounds like too much work and you’re fed up with the powdery mildew on your plants, you can always go with low-maintenance artificial plants that look just like the real thing.
Sources:
- Sam Schmitz, horticulturist with Ball Horticultural Company
- Jessie Liebenguth, horticulturist with Reiman Gardens at Iowa State University
- Lindsay Pangborn, gardening expert with Bloomscape
