Disease

Early and late blight

Tomato and potato diseases: slow target-ring spots (early) or fast black rot (late).

What you'll see

• Early blight: brown spots with target-like rings and a yellow halo, starting on the lowest leaves.
• Late blight: fast-spreading brown-black patches on leaves and stems, with white fuzz underneath when humid.
• Late blight: firm, greasy brown blotches on tomatoes, or reddish-brown rot under potato skins.

Why it happens

Early blight is a fungus that survives on old plant debris. Late blight is a water mold that blows in on the wind in wet weather and can strip a plant in about two weeks.

How to fix it

1. Early blight: remove spotted lower leaves, mulch to stop soil splashing up, and water at the base.
2. Late blight: pull and bag infected plants at once, and never compost them.
3. A copper spray at the first sign of early blight may protect healthy leaves; use it exactly as the label says and keep kids and pets away.
4. Potatoes with late blight: cut off the top growth, wait about two weeks, then dig, and don't store damaged tubers.

Keep it from coming back

• Grow tomatoes and potatoes in new ground for 2 to 4 years.
• Use certified disease-free seed potatoes and resistant varieties.
• Stake, space and mulch plants, and avoid wetting the leaves.

Read more

• Watering a vegetable garden

Sources

• UC IPM: Early blight on tomatoes
• UC IPM: Late blight
• NC State Extension: Early blight of tomato
• RHS: Potato blight

General guidance, not a diagnosis. For valuable, edible or outdoor crops, check with a local extension service or plant expert. Use any product exactly as its label says, and keep children and pets away while it dries.