12 Steps to Prevent & Manage Fungal Diseases on Tomato Plant Leaves: Identifying Septoria Leaf Spot and Early Blight

Of course, we love and want our tomato leaves to be green and healthy all the time but the truth is, especially lower tomato leaves, tend to yellow, brown, and get beat up over the growing season. Sometimes, and more often than not, this is normal die off. I wanted to address a pattern on leaves that often signifies Septoria leaf spot or early blight. This pattern is of concern and requires treatment.

When you see spots that are made up of  brown circles with circles or concentric rings, the pattern is most likely caused by the active fungus on the tomato leaf. Follow The Rusted Garden Journal as I will be writing extensively on how to identify problems in the garden. Today's focus is on identifying spots with concentric rings.

Addressing leaf spots first involves identifying the cause of the spots and then implementing appropriate treatment to address the issue. There are various types of leaf spots that can show up on tomato plants, including fungal, bacterial, and viral diseases. Here are some general guideline to address fungal issues and other problems on your tomato plants.

What are these spots on tomato leaves?

Identify the cause: 

Examine the spots on the tomato leaves and try to determine the cause. Fungal leaf spots often have distinct patterns and colors compared to bacterial or viral spots. This step is crucial because different problems require different treatments.

Keep a journal:
Write down the dates leaf problems show up on your garden plants. Make notes on that weeks temperatures, amount of rain, and humidity. This information can be used to create a prevention spraying routine for your garden.

Create and implement a preventative spraying routine:

Problems that show up once in a garden often return around the same time year to year. Creating a preventative spraying routine that starts two weeks before the problems arrive, can prevent the diseases from taking hold on your plants.

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Prune affected leaves: 

If the leaf spots are localized and not widespread, carefully prune the affected leaves to prevent the disease from spreading more quickly across plant leaves. It is more important to quickly implement a spray treatment to address fungal outbreaks on leaves than it is to remove leaves.

Improve air circulation: 

Ensure proper spacing between tomato plants to allow for adequate air circulation. Good airflow helps reduce humidity levels around the plants, which can inhibit the growth and spread of fungal diseases. It keeps the leaves drier and it lets in sunshine.

Water properly: 

Avoid overhead watering, especially in the evening, as wet foliage can promote the development of fungal diseases. Instead, water at the base of the plants early in the morning to give the leaves a chance to dry during the day. This is best practice but often not the main cause of spreading the diseases.

Mulch: 

Apply a layer of organic mulch around the base of the plants. Mulching helps prevent soil-borne pathogens from splashing onto the lower leaves and reduces weed competition.  Weeds can often serve as a host for diseases. Continue to apply mulch over the season, as needed, to maintain a barrier between the soil and lower plant leaves.

Fungicides: 

If you determine that the leaf spots are caused by a fungal disease, consider using a fungicide. Copper-based fungicides (organic), baking soda spray (organic) wettable sulfur spray (organic) or those containing chlorothalonil (not organic) are commonly used for tomato diseases. Always test spray any new spray you use in the garden on a couple of leaves. Wait 24 hours to see if the spray causes damage before spraying your entire plant.

Crop rotation: 

Avoid planting tomatoes or other members of the Solanaceae family (peppers, eggplants) in the same location each year. Crop rotation can help reduce the buildup of soil-borne pathogens. This is more important on larger scale farms verses a typical home garden. General rotation in a home garden doesn't provide adequate distancing from the previous grow area.

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Resistant varieties: 

When selecting tomato varieties, look for those that are resistant to common tomato diseases, including leaf spots. Resistant varieties can significantly reduce the likelihood of disease development. The harder it is for a fungal disease to establish and take hold, the more effective your preventative spraying and management routines will be. 

Sanitation: 

Practice good garden hygiene by removing fallen leaves and plant debris. Clean garden tools after use to prevent the spread of the diseases or pathogens. This is best practice. It reduces the chances of future problems but remember the issues did show up when your garden was brand new. Spores float in the air and find weeds as hosts.

Monitor regularly:

Regularly inspect your tomato plants for any signs of leaf spots or other issues is one key to reducing significant outbreaks and crop loss. Early detection can help you take timely action before the problem becomes severe. Early detection is important as is the use of preventative spraying. 

Septoria Leaf Spot or Early Blight: Concentric Rings

It takes time to understand the patterns that 'will' show up on your tomato leaves year after year. It is common for tomato plants to have lower leaves that turn yellow, get brown patches, or just plain look beat up. We consider this normal die off that often occurs during the high heat periods of summer. The most important clue that there is a fungal issue like Septoria leaf spot or early blight is the concentric brown rings that form the brown spots and a yellow halo around the outer edge of the spots. The halo means the fungi are alive and active. After spraying, the brown spots will remain but the yellow halo will be gone indicating the fungus is no longer present.

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Cheers!

Gary (The Rusted Garden)

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