Late Blight
Large greasy grey-green to brown blotches that spread across leaves and stems within days, often with a soft water-soaked edge. There are no target rings as in early blight and no small round grey-centred spots as in septoria, and in damp mornings a white downy fuzz shows on the underside of the blotch.
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.
1Pull and bag infected plants
Remove the whole plant, seal it in a bag for the bin, and do not compost it.
heavy duty contractor trash bagsTry this first2Destroy leftover potatoes
Dig out volunteer potatoes and cull piles in spring, because overwintered tubers are the usual starting point.
3Plant certified seed potatoes and clean transplants
Buy certified seed potatoes and inspect bought tomato transplants for blotches before planting.
certified seed potatoes for planting4Protectant fungicide ahead of a wet spell
Copper or chlorothalonil applied before cool rainy weather arrives and renewed after rain, following the label.
copper fungicide concentrate5Grow resistant varieties
Mountain Magic, Defiant and Iron Lady tomatoes carry real late blight resistance.
late blight resistant tomato seeds6Space and stake for airflow
Wide spacing and trellising let the canopy dry, which shortens the wet period the pathogen needs.
garden trellis stakes
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Which plants get late blight
Every plant we cover that gets late blight, 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.
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 Solanaceae, with 6 of the 6 affected plants.
- Solanaceae6 plants
When to treat
Act the day you find it: this disease can wipe out a tomato or potato patch in under a week in cool wet weather, so pull and bag the plants immediately instead of trying to spray your way out of an established infection.
Timing only — the label is the law
This page tells you when to watch for late blight 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 late blight, 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.