Blight on tomato plants

Common on tomato and potato plants, early blight is caused by the fungus Alternaria solani and occurs throughout the United States. Symptoms first appear on the lower, older leaves as small brown spots with concentric rings that form a “bull’s eye” pattern. As the disease matures, it spreads outward on the leaf surface causing it to turn yellow, wither and die. Eventually the stem, fruit and upper portion of the plant will become infected. Crops can be severely damaged.

Early blight overwinters on infected plant tissue and is spread by splashing rain, irrigation, insects and garden tools. The disease is also carried on tomato seeds and in potato tubers. In spite of its name, early blight can occur any time throughout the growing season. High temperatures (80-85˚F.) and wet, humid conditions promote its rapid spread. In many cases, poorly nourished or stressed plants are attacked.


  1. Prune or stake plants to improve air circulation and reduce fungal problems.
  2. Make sure to disinfect your pruning shears (one part bleach to 4 parts water) after each cut.
  3. Keep the soil under plants clean and free of garden debris. Add a layer of organic compost to prevent the spores from splashing back up onto vegetation.
  4. Drip irrigation and soaker hoses can be used to help keep the foliage dry.
  5. For best control, apply copper-based fungicides early, two weeks before disease normally appears or when weather forecasts predict a long period of wet weather. Alternatively, begin treatment when disease first appears, and repeat every 7-10 days for as long as needed.
  6. Containing copper and pyrethrins, Bonide® Garden Dust is a safe, one-step control for many insect attacks and fungal problems. For best results, cover both the tops and undersides of leaves with a thin uniform film or dust. Depending on foliage density, 10 oz will cover 625 sq ft. Repeat applications every 7-10 days, as needed.
  7. SERENADE Garden is a broad spectrum, preventative bio-fungicide recommended for the control or suppression of many important plant diseases. For best results, treat prior to foliar disease development or at the first sign of infection. Repeat at 7-day intervals or as needed.
  8. Remove and destroy all garden debris after harvest and practice crop rotation the following year.
  9. Burn or bag infected plant parts. Do NOT compost.

George WeigelThere’s a big difference between plants suffering from blight (shown here on a tomato leaf) and roots rotting from soggy soil.

Q: I live on a piece of property with numerous natural springs that never dry out, and this year my soil was wet the majority of the spring. For the past 3 years, I have been battling blight in my soil that has been affecting my tomatoes. This year, with all of the rain, it seems that everything in my vegetable garden, including my new strawberry patch and many of my flowers, have been affected as well. How do I get rid of the blight?

A: There’s a difference between tomato blight and more basic rotting of roots from soggy soil.

Blight is a general term for several kinds of fungal diseases. Each one affects only certain plant species. The treatments include planting disease-resistant varieties, removing diseased leaves, inoculating the soil with beneficial fungi that attack the disease-causing fungi and spraying fungicides.

No one blight disease would cause the widespread problems you’re having. In other words, late blight disease can spread from tomatoes to potatoes (same family), but it wouldn’t kill off your strawberries, cucumbers or flowers.

I suspect your main problem is plant roots suffocating from lack of oxygen in water-logged soil.

The best solution for that is creating raised beds so your roots are up and out of the wettest soil. Work enough compost and good-quality topsoil into your soil so your beds are 4 to 6 inches high.

Edge them in stone, brick or wood if you like. Or just rake them into raised areas that are about 4 feet wide — enough for you to reach into the middle from either side. In a flower bed that you’re not regularly harvesting, just raise the beds and taper the front down slightly below the lawn level so you’ll have a little lip to keep mulch from spilling out.

I think that’ll solve most of your problem, but you may well have disease in the soil, too. Early blight and septoria leaf spot of tomatoes are very common diseases and overwinter in soil to re-infect new plants.

Rotating your crops helps, but in small gardens, it’s hard to move your plants far enough to avoid infection.

If you’re not a spray-oriented person (copper is an organic fungicide, Daconil is the most common chemical tomato fungicide), try solarizing your soil. That involves leaving it unplanted while you stretch clear plastic over the beds for about 8 weeks in June, July or August. The sun heats the soil underneath enough to kill disease spores.

Work a little compost into the soil after solarizing.

Fighting Tomato Blight

Tomato blight refers to a family of diseases caused by fungus-like organisms that spread through potato and tomato foliage, particularly during wet weather. Blight spreads quickly, causing leaves to discolor, rot and collapse. The two best known varieties are early blight, caused by Alternaria solani fungal spores and late blight, a result of Phytophthora infestans spores (“Phytophthora” aptly translates to mean “plant destroyer”). The former striking early to mid-season and the latter mid-to-late, blights are the bane of many home growers, rapidly attacking tomato plants and abruptly halting production as it spreads quickly through the garden.
Early blight is characterized by concentric rings on lower leaves, which eventually yellow and drop. Late blight displays blue-gray spots, browning and dropped leaves and slick brown spots on fruit. Although the diseases are caused by different spores, the end result is the same. For tomato and potato growers, blight can be devastating.
As temperatures rise and rainfall increases, risk of infection is high in home gardens. The best offense is a good defense when contending with tomato blight. An undetected infection can quickly put an end to summer tomato and potato crops, but steps can be taken to rescue at-risk plants. If tomato blight has reared its ugly head in the garden this year, a change in maintenance and tactics to limit the spread of the disease may prevent drastic plant losses.
Select resistant plants. Some tomato plants have been developed to reduce susceptibility to blight issues. When purchasing plants, look for blight-resistant varieties and always purchase from reputable sources.
Rotate crops Plant tomatoes in a different part of the garden each year and avoid planting near potatoes, in which late blight may overwinter.
Allow space between plants. Blight thrives in wet conditions. Give plants plenty of room to provide good airflow and use stakes or cages to keep vines off the ground.
Mulch. Applying mulch around the base of tomato plants cuts back on the spread of spores that cause blight. If blight becomes a problem, surrounding mulch may harbor spores and should be disposed of off-site (do not compost infected plants or mulch).
Water from below. Using drip irrigation or soaker hoses to water the soil around the base of plants helps keep foliage dry, cutting back on the spread of blight.
Inspect plants frequently. Catching blight early can be effective in preventing spread between plants. If blight is detected on shoots or leaves, remove them from the plant and dispose of diseased foliage off-site. Blight spreads quickly, and in some cases destroying entire plants may be necessary to protect adjacent crops.
Treat organically. Copper fungicides can be effective in combating blight, but must be carefully applied. Follow manufacturer instructions, wear protective clothing during application and always wash fruit before consumption.

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