Plant disease
Blight
The catch-all name for brown, spreading dead patches on leaves.
Blight is in its active season now — scout your plants this week.
How to identify blight
'Blight' is a general word gardeners use for any disease that browns and kills leaf and stem tissue in fast-spreading patches. Many different fungi cause it across many crops, so the exact look varies: irregular brown dead blotches, sometimes with a yellow halo, that grow and run together in wet weather.
If your problem is on tomatoes or potatoes, name it more precisely — see early blight (slow, target-ring spots on lower leaves) and late blight (fast, greasy dark blotches with white fuzz underneath). Pinning down which one changes how urgently you act.
For most other vegetables, the general management below applies whatever the specific fungus, because the drivers are the same: wet leaves, crowding, and infected debris.
Attacks: Tomatoes, Potatoes, Beans, Carrots, Celery, Cucurbits, Many vegetables
Life cycle: Most leaf blights overwinter in old plant debris and soil, then spread by splashing rain and wind onto wet foliage. Warm, humid, crowded conditions let them jump plant to plant and build through the season.
Signs of blight
What you actually see on the plant — usually before you spot the pest itself.
- Brown dead patches on leaves and stems that spread in wet weather
- Yellowing around the lesions, then whole leaves browning off
- Damage worst in the crowded, still center of the planting
- Rapid spread after a warm, rainy stretch
Organic control, least-toxic first
Start at the top and only move down if you need to. Physical and cultural fixes come before any spray.
- Remove and trash affected foliage
Snip off blighted leaves and stems as soon as you see them and bag them for the trash, not the compost. Getting infected tissue out of the bed slows the spread more than any spray.
- Open up airflow
Thin, stake, and widen spacing so leaves dry fast and humidity drops around the plants. Still, crowded air is what most blights need to spread.
- Water at the base, never overhead
Overhead watering wets the leaves and splashes spores around. Water the soil in the morning so any foliage that does get wet dries quickly.
- Apply a registered organic fungicide if it persists
If the disease keeps advancing, a registered copper fungicide can protect healthy leaves. Start early, before it takes over, and reapply on the label's schedule and after rain.
- Rotate the crop next season
Move the affected crop family to a new bed so last year's debris-borne spores have no host to reinfect.
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One rule for any product you spray: follow the label. The label is the law, and it is the tested, safe rate for your plants — homemade mixes and dish-soap sprays are not, and can scorch foliage.
Prevent it next season
- Space and thin for airflow so leaves dry quickly
- Water at the base in the morning, not over the leaves
- Mulch to stop rain from splashing soil-borne spores upward
- Clear and trash plant debris at season's end
- Rotate crop families on a 2-3 year cycle
Questions about blight
My plant has blight — what kind is it?+
'Blight' is a general term for spreading brown leaf death. On tomatoes and potatoes, figure out whether it's slow-moving early blight (target-ring spots low down) or fast, deadly late blight (greasy dark blotches with white fuzz). On other crops, the general steps below apply.
How do I stop leaf blight from spreading?+
Remove and bag the affected leaves, improve airflow with spacing and thinning, water only at the base, and use a registered copper fungicide preventively if it keeps moving. Then rotate the crop next year.
Plan a garden that fights back
Healthy, well-spaced plants shrug off pests that flatten a crowded bed. PlotToTable sizes your beds, spaces every crop, and flags the pests that hit what you grow.