Tomato Blight

tomato blight on plants

Tomato Blight

Anyone who grows tomatoes has experience with tomato blight.  It is just one of the things that happen in a garden.  If you are going to be successful at raising tomatoes, it is essential that you have an understanding of tomato blight, what causes it, and how to deal with it.

What is it?

Tomato Blight is a fungal disease.  It is usually characterized by a gradual yellowing of leaves at the bottom of the plant that slowly works its way up the plant to the top.  The true name of this disease is southern blight or early blight.  These are fungal diseases.  This time of year, the most common strain is early blight. 

How do I Spot It?

tomato blight leaf spots

The early signs of blight are yellowing of leaves near the bottom of the plant and black spots with a yellow ring around the black spot.  Black spots with a yellow ring are called a halo.  The fungus that causes can be two species; A. tomatopila or A. solani.  It isn’t really important which one you have; it is important that you understand how to treat it to keep your tomatoes healthy and producing through the season.

These fungal diseases can exist in any soil and at any time.  However, warm, damp weather accelerates their growth and the damage they can do to your plants.  Blight can affect stems, leaves, and fruit, but is usually seen first at the base of the plant with the lowest leaves being infected.

How do I Prevent it?

Water your plants carefully.  The fungus needs moisture to multiply and care in watering will help control the spread.  Water at the base of the plant slowly and allow the moisture to infiltrate.  Mulch around the plant will help by keeping moisture in the soil while staying dry on top, which inhibits the production of spores.  Water in the mornings to keep plants dry during the day and try to minimize water on the foliage of the plant.  Overhead watering with a sprinkler is a bad idea with tomatoes.

Rotating your crops will also help minimize the exposure to blight. Remember that you should rotate your crops by family since diseases and pests are usually planted family specific.  If you plant tomatoes after a bed has been planted in potatoes, you can exacerbate your blight problem.  Potatoes and tomatoes are in the same family and blight can affect both.

Allow good spacing plans for your plants.  Tomatoes need airflow in and around the plants to remain healthy and to aid in pollination.  Planting too close will crowd the foliage, inhibit airflow, and allow the spores of the fungi to spread quickly.  Good airflow also helps keep your foliage dry.

How do I Treat it?

tomato blight and compost tea

There are several organic treatments for blight.  You can add cornmeal to the soil around your plants.  Cornmeal, particularly gluten cornmeal, contains a compound that acts as a natural pre-emergent and will help keep the spores from germinating.  Spraying regularly with compost tea, especially if mixed with garlic juice, will also help prevent blight from getting a foothold.

Take Heart

The truth is that if you grow tomatoes, you are going to have blight to a certain extent.  Good practices and good management in the garden will go a long way to keeping the problem in check and allowing your tomato plants to have a full and productive season.

Links and Resources

For more information about organic gardening, lifestyles, and living, visit our website at West Texas Organic Gardening.

If you found the information here helpful, you might also find these articles on our website of interest.

Tomatoes – Pruning

Tomatoes – Propagation

Secrets to Growing Tomatoes in West Texas

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