Septoria Leaf Spot of Tomato Plant: Identification, Control & Prevention

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Quick Answer: Septoria Leaf Spot of Tomato Plant

Septoria Leaf Spot of the tomato plant is also called ‘Blackspot or Black speck.’ Septoria leaf spot is a fungal disease favoured by high humidity and wet climate. The prominent circular black spots in clusters are seen in the diseased leaflets of the tomato plants. Another very noticeable sign of septoria leaf spot is white growth on the part of stems that are directly touching the infected leaves. A fungicide containing copper can be an effective method of controlling it.

This is an informative and practical guide for the Septoria Leaf Spot of the tomato plant. 

Let us get started!

What is Tomato Septoria Leaf Spot Disease?

Septoria Leaf Spot is a fungal disease caused by ‘ Septoria lycopersici.’  This fungus can survive in infected soil debris for years. It can affect the tomato plant at any stage of development. 

Septoria Leaf Spot pathogen infects older leaves before spreading its infection to young or adult plant parts. It affects young, adult, and older leaflets of tomato plants. Stems are also prone to severe damage by Septoria leaf spot.

These spots develop into deep brown spots surrounded by halo [circle of white color].  The leaves then wilt and die. The dead leaves expose the fruits to sunburn.

Eventually, the infection spreads to the green and ripened tomato fruit and the plant dies.  

Conditions Which Favour Fungi Septoria Leaf Spot

Tomato plants are more susceptible to septoria leaf spot disease in heavy rains. Heavy rains account for high moisture content in the air, thus, providing optimum conditions for the mycelium growth of S. lycopersici.  

Temperature range between 10-25 degrees Celsius favours the maturation of the septoria leaf spot pathogen. However, the temperature of 20-25 degrees Celsius with 90-100% humidity provides optimum conditions for its rapid growth.

The initial marks of Septoria Leaf Spot are observed on older leaves. These marks are ‘Small, circular black spots.’ These spots are found in clusters which later spread on the entire leaf.

How does Septoria Leaf Spot Harm Tomato Plants?

Septoria leaf spot pathogen survives in the soil on plant debris. It also lives on several Solanaceous hosts. It can also be transmitted through gardening equipment. 

How Septoria leaf spot Fungi spreads

Septoria leaf spots are spread through water splashing, wind, cultivators, human contact, and insects.

Conidia [asexual spore of fungi] contains mycelium [contains hyphae that help in penetration] that invades the bottom leaves of the tomato plant and germinate within 48 hours of the invasion. Leaf spots can appear within 5 days of germination.

Infection of septoria leaf spot is majorly through stomata. Mycelium penetrates through stomata and later affects the tissues. 

The septoria leaf spot pathogen reaches the bottom leaves by external factors. The infection then travels through the inner filaments and reaches the stems. The vascular system of the tomato plant might get affected. 

Leaves die within 7-10 days of germination and expose fruits to sunburn. Fruits are always the last part to get caught an infection.

Septoria leaf spot might not kill your entire tomato plant but will lower the quality and quantity of tomato yield. It will also infect the healthy soil debris of your tomato plant, which could be a crisis in future.

Watch this video as regards Septoria Leaf Spot-

How to Confirm that Septoria Leaf Spot is Troubling your Tomato Plants?

Septoria leaf spot has a very distinguished sign i.e., ‘Clusters of Black spots’. However, there are many minute yet notable symptoms that can help you identify this disease. The symptoms of septoria leaf spot disease can be seen on foliage, stems, calyxes, blossoms and very rarely fruits.

Initially, septoria leaf spots infect the lower side of the leaf. Small circular and moist spots appear on the leaf of the old leaves. The diameter of these spots is generally between 1.6- 3.2 mm diameter.

These spots begin as yellow spots with a grey centre and dark border. These yellow spots become brown with a diameter of 2-6mm. 

These grey centres contain tiny black specks with pycnidia [fruiting bodies of fungi that release infected spores].

A yellow halo surrounds the spots. After the release of spores [conidia] from pycnidia, the grey center turns whitish in appearance.  

This spore’s production occurs on the entire leaf causing the leaf to look like a dry, yellow leaf with little clusters of black spots.

Leaves eventually coalesce, turn brown, wilted, dry and die. Defoliation progresses from the base of the plant to upwards affecting lower leaves then upper leaves and stems. 

Dead septoria-infected Leaves.
   Infected leaf with black spots and yellow halo around them
    The whitish appearance of burst pycnidia 

A noticeable white growth is seen on the stems touching the infected leaves. The upward stems might turn golden-yellow.

These symptoms of the stems indicate that the Septoria Leaf spot has infected almost an entire plant. Lesions on the stems are generally dark elongated spots which also bear pycnidia.

It is due to the drying of leaves and weakening of stems; leaflets die and fall off. This leads to the sunscald of fruits.

Fortunately, septoria leaf spot disease does not affect tomato fruits directly.

  White appearance on the stems
 Brown lesion seen on the stems

Ways to Control Septoria Leaf Spot Disease on Tomato Plant

Controlling the spread of septoria leaf spot after spotting the initial sign of disease can be done in a Step by Step manner Like this –

Step 1: Halt The Spread

The first step to halting disease spread is to keep the garden clean. 

  • Remove the infected stems and leaves. 
  • Do not compost them either burn or throw infected leaves.
  • Disinfect the gardening tools used for removing the leaves and stems.
  • Do not let any infected leaf fall on the ground. 
  • Monitor your tomato plants daily to get updates about their growth and infection.

Garden sanitation is vital as any infected leaf or stem might become the source of infection in the future.

This would ensure that no healthy plants are at risk of developing the disease.

Check out this video for controlling septoria leaf spot –

Step 2: Use Fungicide

The second step is to spray fungicide routinely.

  • Copper, maneb, mancozeb, thiophanate-methyl, benomyl, chlorothalonil, tolylfluanid are chemicals that are proven effective against septoria leaf spot of the tomato plant.
  • Apply at an interval of 1-2 weeks during the growing season.
  • Avoid spraying fungicides during the evening, as they could burn your leaves.
  • Make sure you test homemade or any new fungicide before spraying it on the entire plant. Spray it on 1 or 2 leaves and leave it on for 48 hours and look for damage if there is any. 
  • You can use 2 parts of baking soda to 1 part of water as a preventative spray.

Fungicides will not cure your infected leaves but protect your healthy leaves from catching the infection.

Check out this video for homemade fungicides-

Step 3: Prevent Dispersion

The third step is to prevent the dispersion of the infected spores. 

  • Do not perform overhead watering. Instead, create trenches so that water reaches just the roots.
  • Avoid touching your plants when they are wet.
  • Make sure your foliage is not wet for too long.
  • Stake, Mulch, and prune your tomato plants to ensure good air circulation and to maintain distance between ground and leaves.
  • Provide the right nutrition to your plants rich in potassium, calcium and magnesium.  Use organic manure using homemade ingredients. This will help your plants to fight against the disease.

Check out this video for natural fertilizers for tomato plant-

Preventing Septoria Leaf Spots

Here are a few practical ways to prevent Septoria Leaf Spots from spreading to your tomato plants –

  1. Use resistant seeds to provide immunity against septoria leaf spots. Resistant seeds might not guarantee complete protection but it will take time to develop the disease. 
  1. Fumigate your soil and make it disease-free. This will ensure the safety of the subsequent cultivation of tomato plants.
  1. Rotate your crops after every two years.
  1. Harvest your tomatoes as soon as possible. Pluck your green or ripened tomato fruits if they are grown on an infected plant. 
  1. Avoid overcrowding of tomato plants. This will help provide air circulation and protect your healthy ones from an infected tomato plant.
  1. Avoid touching leaves with the ground or soil. 
  1. Keep removing beetles or insects resting on your leaves or stems. They might act as the source of infection.

FAQ’s

Can I eat tomatoes with septoria leaf spot?

Yes, you can definitely eat tomatoes with septoria leaf spot. This disease does not cause any harm to fruits and is fit for edible purposes.

Can septoria leaf spot be cured?

No, but by using fungicides and other control measures, you can protect your healthy tomato plants from septoria leaf spot. 

How is leaf septoria different from the blight disease of tomato plants?

Spots caused by Septoria are more regular and numerous. Their centres are clearer and do not show concentric patterns.

How to protect your plant from septoria leaf spot after harvesting?

Plant debris should be buried deep after harvest. This will protect your future plants from developing the infection.

How to protect leaf septoria naturally?

You can use mixture of aspirin, baking soda and water.  
You can also use neem oil as an active ingredient of homemade sprays. 

Summary

I am hopeful that this detailed guide will help you understand, identify, and control / prevent septoria leaf spot in tomato plants.

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