Downy Mildew
Yellow angular patches on the top of the leaf with gray-purple fuzz on the underside directly beneath — the opposite geography of powdery mildew, and it wants WET nights, not dry ones. Basil, cucurbits, and grapes are the frequent victims.
Disease checklist
Four things to look for. If most of them match what you are holding, you are in the right place.
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.
1Water the soil, not the leaves
The spores need hours of leaf wetness to infect; morning drip irrigation denies them the window.
Try this first2Pull badly infected plants
Basil especially: once fuzz shows on the undersides, that plant is a spore factory and the harvest is done. Bag it, do not compost it.
3Copper fungicide as protection
Copper protects clean leaves ahead of infection on the label's schedule; it cannot cure what is already fuzzy.
copper fungicide spray garden
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Which plants get downy mildew
Every plant we cover that gets downy 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.
annuals15
BasilOcimum basilicumdevastating
Bok ChoyBrassica rapa subsp. chinensis
BroccoliBrassica oleracea var. italica
CauliflowerBrassica oleracea var. botrytis
ColeusColeus scutellarioides
CucumberCucumis sativus
Holy Basil (Tulsi)Ocimum tenuiflorumless prone than sweet basil
ImpatiensImpatiens wallerianadevastated old strains; buy resistant 'Beacon'/'Imara'
LettuceLactuca sativa
Luffa GourdLuffa aegyptiaca
Pansy & ViolaViola × wittrockiana
QuinoaChenopodium quinoain humidity — its main enemy
SpinachSpinacia oleracea
Stock (Gillyflower)Matthiola incana
SunflowerHelianthus annuus
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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 Brassicaceae, with 4 of the 17 affected plants.
- Brassicaceae4 plants
- Lamiaceae3 plants
- Amaranthaceae2 plants
- Asteraceae2 plants
- Cucurbitaceae2 plants
When to treat
Treat it when you see it, and start earlier next year if it comes back. It follows wet nights.
Timing only — the label is the law
This page tells you when to watch for downy 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.
Other problems on the same plants
If a plant gets downy mildew, these are the problems it most often gets as well, so they are worth checking for while you are out there. They tend to appear together; one does not cause another.