Powdery Mildew

A white, flour-like coating that wipes off with a finger, starting in patches on the oldest leaves and spreading until the plant looks dusted. Unlike most fungi it thrives in DRY weather with cool nights — squash, cucumbers, bee balm, and lilacs are regulars.

Disease59 plants we cover get powdery mildewmostly perennials

Disease checklist

Four things to look for. If most of them match what you are holding, you are in the right place.

White powder that wipes off with a finger
Starts on the oldest, lowest leaves
Round patches that spread and join up
Worst in dry spells with cool nights

What gets rid of it

Gentlest option first. For most backyard cases the first one is enough, so try these in order and stop as soon as it works. If you do spray something, the product label tells you how — please read the notice further down.

1Open up the airflow
Thin crowded stems and give plants their full spacing; stagnant humid air around leaves is what lets spores take.
Try this first
2Potassium bicarbonate spray
Changes the leaf surface pH; knocks back active mildew rather than just preventing it.
potassium bicarbonate fungicide
3Horticultural oil or neem
Both suppress spread on the label's schedule when caught early.
neem oil concentrate plants
4Plant resistant varieties next year
Squash and cucumber breeding has largely solved this; look for PM-resistance codes in catalogs.

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Which plants get powdery mildew

Every plant we cover that gets powdery mildew, grouped by type — tap any one to open its page. A note beside a plant came from that plant’s own entry, because the same disease can be a minor nuisance on one plant and a serious problem on another. Plenty of plants we do not cover get it too.

trees6

shrubs9

vines3

perennials24

annuals12

bulbs3

succulent1

KalanchoeKalanchoe blossfeldiana

houseplant1

African VioletStreptocarpus ionanthus

Plant families hit hardest

Related plants often share the same problems, so if one plant in a family has it, check the others. The largest group here is Asteraceae, with 12 of the 59 affected plants.

Asteraceae12 plants
Lamiaceae6 plants
Fabaceae5 plants
Ranunculaceae5 plants
Cucurbitaceae4 plants
Rosaceae3 plants
Caprifoliaceae2 plants
Grossulariaceae2 plants

When to treat

Treat it when you see it. There is no season to wait for.

Timing only — the label is the law

This page tells you when to watch for powdery mildew and when treating is worth considering. It is not a recommendation to apply any particular product. Read and follow the product label before you spray — under federal law the label is the legal instruction, and using a pesticide against it is illegal.

Check the pre-harvest interval. Every product that’s cleared for an edible crop sets a minimum number of days between spraying and picking. Find it on the label before you spray anything you intend to eat.
Check the re-entry interval before you or anyone else works in the treated area again, and use the protective equipment the label names.
Confirm the product is registered for your crop in your state. This page groups many different crops together, and a product legal on one of them is not legal on all of them — state registrations differ too. Your state pesticide agency or local extension office can confirm both.
Rates and mixing instructions come from the label, never from us. We don’t publish them because they differ by product and formulation.