What blight is and how to spot it on your tomatoes

Blight is a fungal disease that spreads fast in warm, wet conditions and kills tomato leaves, stems, and fruit. Two types attack tomatoes: early blight (which starts on lower leaves as brown spots with concentric rings) and late blight (which appears as water-soaked patches on leaves and stems, often with white mold on the undersides). Both spread through soil splash, contaminated tools, and air currents, and both can destroy a plant in weeks if left untreated.

Early blight usually shows up first on the lowest leaves once the plant is established and the weather turns warm and humid. Late blight arrives later in the season and moves faster—it thrives in cool, wet conditions and can infect fruit still on the vine. The difference matters because the treatment changes slightly depending on which one you have.

Key Takeaways

  • Remove infected leaves as soon as you see brown spots or water-soaked patches, cutting at least 6 inches below the damage to stop the fungus from spreading upward.
  • Spray the plant with copper fungicide or sulfur every 7 to 10 days once blight appears, coating both the tops and undersides of leaves thoroughly.
  • Space plants far enough apart to allow air to move between them, water only at the soil level (never on leaves), and remove fallen leaves and debris from the ground.
  • Stake or cage tomatoes to keep foliage off the soil, where fungal spores live and splash onto lower leaves during rain or watering.
  • Pull up and discard the entire plant at the end of the season rather than composting it, since blight spores survive in plant material.

Remove infected leaves and stems when ready

The moment you see blight symptoms, cut off the affected leaf or stem with clean pruning shears or a knife. Disinfect your tool between cuts by wiping it with rubbing alcohol or dipping it in a 10 percent bleach solution (one part bleach to nine parts water). This stops you from spreading the fungus from one plant to another or from one part of the plant to another.

Always cut at least 6 inches below the visible damage, because the fungus spreads inside the plant before it shows on the surface. Bag the infected material in a sealed plastic bag and throw it in the trash—do not compost it, because the spores survive composting and will contaminate your soil next year. If the disease has already killed most of the lower leaves, you can remove entire branches back to the main stem.

explore fungicide spray on a schedule

Once you have removed the infected parts, spray the entire plant with a fungicide every 7 to 10 days. Copper fungicide and sulfur are the most common choices for home gardeners and work on both early and late blight. Follow the label directions for mixing and how often to spray—most copper products are mixed at a rate of 1 to 2 tablespoons per gallon of water, but this varies by brand.

Spray in the early morning or late evening when the sun is low, because spraying in direct heat can burn the leaves. Coat the tops and undersides of all remaining leaves, the stems, and the soil around the base of the plant. Reapply after rain, since water washes the fungicide off. If you choose sulfur, do not use it within two weeks of a copper spray, and do not use it if the temperature is above 85 degrees Fahrenheit, because it can damage the plant.

Space plants and water at soil level only

Blight spreads through water droplets, so the way you water and arrange your plants matters as much as the fungicide. Water only at the base of the plant, directing the hose or watering can at the soil—never spray water onto the leaves. Wet foliage creates the humid conditions the fungus needs to grow, and water splash from the soil carries spores up onto the lower leaves.

Plant tomatoes at least 24 to 36 inches apart so air can move freely between them. Crowded plants stay wet longer after rain or watering, which gives the fungus time to take hold. Prune lower branches so the lowest leaves are at least 12 inches above the ground, keeping foliage away from the soil where spores live. Remove fallen leaves and debris from the ground around the plant every few days during the growing season.

Use stakes or cages to keep plants off the ground

Tomatoes that sprawl on the ground are more vulnerable to blight because their leaves touch the soil and pick up spores. Stake or cage your plants from the time they are young so the stems and foliage stay elevated and air can circulate underneath. This also makes it easier to remove lower leaves and inspect the plant for early signs of disease.

As the plant grows, tie the main stem loosely to the stake with soft ties or strips of cloth, leaving room for the stem to expand. Prune side shoots (called suckers) that grow between the main stem and branches, which improves air flow and reduces the number of leaves that can get sick. The goal is an open structure where you can see into the plant and water and air can reach all parts.

Clean up and replace soil at the end of the season

At the end of the growing season, pull up the entire plant—even if it looks healthy—and throw it in the trash. Do not compost it. Blight spores survive in dead plant material and will infect your tomatoes again next year if you work that compost into your soil.

If you grew tomatoes in the same spot this year, consider planting something else there next season, or at minimum remove the top 2 to 3 inches of soil where spores have settled. If you use the same stakes or cages, wash them with a 10 percent bleach solution before storing them. Rotate tomatoes to a different part of the garden each year if you can, because this breaks the cycle of spores building up in the soil.

Choose resistant varieties for next year

Some tomato varieties are bred to resist early blight, late blight, or both. Look for varieties labeled with EB (early blight resistance) or LB (late blight resistance) on the seed packet or plant label. Common resistant varieties include Mountain Magic, Iron Lady, and Defiant PhR, though availability changes by region and seed company.

Resistant varieties are not immune—they still need good spacing, air flow, and careful watering—but they give you a head start. If you live in a region where late blight is common (cool, wet climates like the Pacific Northwest or the Northeast), choosing a resistant variety can be the difference between a harvest and a total loss.

Frequently Asked Questions

Can I eat tomatoes from a plant with blight?

If the fruit itself shows no spots or soft areas, it is safe to eat. Blight infects the leaves and stems first, and fruit later. Wash the tomato and cut away any damaged parts. If the fruit has water-soaked patches or is soft, throw it away. Once fruit is infected, the disease spreads quickly and the tomato will rot.

What is the difference between early blight and late blight?

Early blight shows brown spots with rings on lower leaves and spreads slowly in warm weather. Late blight causes water-soaked patches and white mold on leaf undersides and spreads fast in cool, wet weather. Both need fungicide, but late blight is more destructive and harder to stop once it starts. Late blight can also infect green fruit on the vine.

Will blight come back next year if I clean up this year?

Blight spores can survive in soil and plant debris, so it may return if conditions are right. Removing all infected plant material, rotating crops, and choosing resistant varieties next year reduce the risk. If blight was severe this year, consider growing tomatoes in containers with fresh soil instead of in the ground.

Is neem oil or insecticidal soap effective against blight?

No. Blight is a fungal disease, not an insect problem, so insecticides and neem oil do not work. Copper and sulfur fungicides are the standard treatments. Some gardeners also use milk spray (one part milk to nine parts water) as a preventive, though it is less reliable than copper or sulfur.

How long does it take for fungicide to work?

Fungicide stops new infections but does not cure leaves that are already infected. You should see the spread slow within a few days of starting treatment, but infected leaves will continue to yellow and die. That is normal—remove them as they decline. It takes consistent spraying every 7 to 10 days for several weeks to bring the disease under control.