Tree problems · Disease
Powdery mildew: signs and what to do
Powdery mildew is a tree disease, often seen on flowering dogwood, crape myrtle, American sycamore. Look for: white to gray, dusty or powdery coating on the top or bottom of leaves.
General information, not a diagnosis. A certified arborist or your county extension office can confirm.
- Disease
- Flowering dogwood
- Crape myrtle
- American sycamore
- White oak
- Bur oak
- Northern catalpa
Signs to look for
Tick what you see. More ticks make it more likely, but only an on-site look can confirm.
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Season
Usually shows from late spring through fall. It is often worst in late summer and early fall, when nights are cool and days are warm.
How it spreads
Spores travel on the wind from leaf to leaf. Unlike many leaf fungi, powdery mildew does not need rain or standing water on the leaf to spread. Crowded, shaded or poorly aired plantings tend to see more of it.
Where it is found
Powdery mildew fungi live in nearly every part of the United States on many kinds of plants, and different species of the fungus attack different trees. Check your state official map; ranges change.
Official sources
What to do
- 1
Look closely first. Make sure the white coating wipes off and is not just dust, spray residue or pollen.
- 2
On a large mature tree, powdery mildew is mostly a looks problem. Healthy trees usually live with it year after year.
- 3
Rake and remove fallen leaves in fall if the problem is heavy on small trees, since the fungus can carry over on old leaves.
- 4
Thin crowded branches and nearby plants so air moves through the canopy.
- 5
If a small, high-value tree is hit every year, ask a local arborist or your county extension office about fungicide timing. Timing and product choice change by region and by label.
Safety first: do not climb, do not cut near power lines and do not use a chainsaw on storm-loaded wood. Call the utility for downed lines and 911 if anyone is in danger.
Prevention
Pick resistant varieties when planting. Many crape myrtle selections are bred for mildew resistance, so ask your nursery or extension office about resistant choices for each species. Give trees full sun where the species wants it, space them so air can move, and water at the base in the morning rather than spraying the leaves.
When to call a pro
Call an arborist if the tree also shows dead branches, thin crown, trunk decay or other stress. Heavy mildew every year on a young or valuable tree is also worth a visit, since the real cause may be site stress.
Not sure who to call? Read how to hire a tree service or check is my tree dangerous?
Trees it affects
Usually seen on: Flowering dogwood, Crape myrtle, American sycamore, White oak, Bur oak, Northern catalpa.
See all species in our tree library, or pick a tougher tree with the tree picker.
For tree companies
How to explain powdery mildew to a customer
Be honest that this is mostly cosmetic on mature trees. Show the homeowner the wipe-off test, explain that shade and poor airflow make it worse, and offer thinning or a resistant replacement only when it truly helps. Do not sell spray programs as a cure for a harmless leaf coating.
Send this page to the customer after your visit so they can read the signs in plain words. See also selling plant health care and the job photo checklist.
Questions
Is powdery mildew going to kill my tree?
Rarely. On established trees it mostly spoils the look of the leaves. Young or stressed trees, or trees hit by other problems at the same time, can be weakened more.
How can I tell it from dust or spray residue?
Powdery mildew is a living fungus that grows on the leaf and looks like white or gray flour. It usually appears in patches and often returns in the same spots each year. Rub a leaf with a finger, then look for new growth of the coating over the next days.
Does it need rain to spread?
No. Many powdery mildews do well in humid air with cool nights and dry leaves. That is why they show up in summers that are not especially wet.
Should I rake up the leaves?
It can help on smaller trees, because the fungus can survive on fallen leaves. It is not a cure, and it matters less on big trees with a lot of canopy.
Do I need a fungicide?
Usually not for a mature shade tree. Fungicides work best as protection before the disease takes hold, and they must be applied by the label. Ask your local extension office or a licensed pro before you spend money.
Can I stop it by planting something different?
Often yes. Choosing a mildew-resistant variety, or placing the tree in better sun and airflow, is the most reliable long-term fix.
Can Lirevon diagnose powdery mildew on my tree?
No. Lirevon is a remote marketing team for tree service companies and does not do tree work. This page is general information, not a diagnosis. A certified arborist or your county extension office can confirm what is wrong with your tree.
How do I find a good local pro for this?
Search Google Maps for certified arborists or tree services near you, read their reviews and ask for proof of insurance. Get two or three written quotes. Our guide on how to hire a tree service lists the questions to ask.
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