Stemphylium Gray Leaf Spot of Tomato Plant: Prevent & Manage

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Quick Answer: Stemphylium Gray Leaf Spot of Tomato Plant

Stemphylium gray leaf spot of the tomato plant is a defoliating infection, usually infecting leaflets of the tomato plant at an early stage. It can affect the plant at any developmental stage. Tomato fruits are prone to sunscald due to the early shedding of leaves. Stemphylium gray leaf spot is a dominant disease in tropical and sub-tropical areas.

This is a detailed reference guide to understanding, preventing, and managing Stemphylium gray leaf spot of the tomato plant in your garden.

Let us get started!

What is Tomato Stemphylium Gray Leaf Spot Disease? 

Stemphylium gray leaf spot of the tomato plant is caused by Stemphylium solani, S. lycopersici (syn. S. floridanum), S. vesicarium, and S. botryosum f. sp. lycopersici. 

These fungi cause their symptoms on leaflets, very seldom on petioles and stem, never on fruits. These spots are initially brownish which is eventually followed chlorosis at the boundary.

Stemphylium gray leaf spot of the tomato is a seed-borne fungus. However, it lives in plant debris and infected soil.  The fungus can remain viable on tomato plants for as long as 5-10 years. 

The identification of the Stemphylium Gray Leaf Spot of the tomato plant is challenging because its symptoms are highly similar to those of other diseases.

The only way to confirm the Stemphylium Gray Leaf Spot of the tomato plant is to look for the spores of the fungi under a microscope. 

The conidia and conidiophores for different stemphylium species are different from each other.

Stemphylium solani –

  • Brown and pointed conidia.
  • Muriform conidia are very brown when mature, rounded at one end, and pointed at the other end.

Stemphylium lycopersici [S. floridanum] –

  • Conidia are muriform, very brown when mature, rounded at one end, and pointed at the other end.
  • Conidia are pointed at one end and are longer [19.9–62.2 × 4.6–23 µm].

Stemphylium vesicarium –

  • Conidiophores have single conidia, brown in color, which are rounded at their ends.
  • Conidia are multicellular, melanized, and rectangular.

Stemphylium gray leaf spot of the tomato plant is prevalent in areas of warm, humid, and wet climates. It is favored by dew. 

The fungus is dispersed through wind current and water splashes. It infects healthy plants through water splashes, human contact, or touching of harvesting cultivars. 

How does Stemphylium Gray Leaf Spot Harm Tomato Plants? 

Stemphylium gray leaf spot reduces the plant yield and sometimes destroys the entire crop of the season.

Conidia germinate and began to infect the leaves in a short period. 

Conidia germination and infection require high humidity or wet leaf surfaces.

The optimal temperature for the disease development is 77 °F. Disease severity was generally high after the beginning of fruits development. 

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

Stemphylium gray leaf spot primarily affects the leaves of the plant.

The symptoms are visible during the initial infection stage; however, for correct diagnosis a proper laboratory examination using a microscope is necessary.  

The symptoms that are seen from naked eyes are-

  • Small, Dark Brown or black and circular specks [a tiny spot] are observed as initial signs of Stemphylium.  
     Small Brown Spots
  • Enlarged brown spots of about one-tenth of an inch in diameter are formed at the later stage of infection.
  • Large veins and secondary veins are affected.
  • A yellow halo might be visible around the spots.
  • The center of the leaf turns grey, dry, and cracked. Under high humidity and heavy dew, fungal spores can be seen either in the center or on the lesions.  
  • Short holes are seen in the center due to the cracking of the leaf. 
  • Leaves become chlorotic, necrotic, and die.
  • Soft and young stems or petioles of the plant might get infected and show long and brown lesions. 
  • Defoliated leaves put the tomato fruits at the risk of sun scalding.

Ways to Control Stemphylium Gray Leaf Spot Disease on Tomato Plant 

The complete healing of the tomato plant from Stemphylium grey leaf spot is nearly impossible but, we can manage the symptoms and can prevent its spread to healthy tomato plants by – 

1. Planting Resistant Varieties

Resistant seeds labeled with V F N A St are effective against the Stemphylium gray leaf spot of the tomato plant. St stands for Stemphylium.

Cultivating resistant seeds is the most economical and reliable method of managing stemphylium gray leaf spot disease.

These varieties do not produce tomatoes with good yield but reduce the risks of the disease.

2. Use Fungicides

Tomato plants that announce the onset of the disease or are susceptible to the infection should get regular doses of fungicides.  

Spraying of the fungicide should be done carefully in the evening. 

Fungicides containing chlorothalonil, mancozeb, and copper produce the best preventative results against stemphylium gray leaf spot disease. 

Always spray the fungicide according to the instructions given.

How to Prevent Stemphylium Gray Leaf Spot on Tomato Plant 

There is no shortcut to protect your tomato from stemphylium gray leaf spot disease.

Just some precautionary measures and you have reduced the risk of the disease by at least 60%.

1. Closely Monitor your tomato plants

Inspect your plants at least two times a week.

Do not leave your foliages wet since wet leaves provide the most suitable condition for disease development.

Overhead watering is always dangerous for your tomato plants. It can increase the risk of water splashing.

Keep looking for beetles and insects resting on your plants.

Keep a tab of your soil conditions. Maintain proper soil pH, water drainage, and soil moisture.

Always remember the content of moisture in soil should always be low and water drainage should be good. 

2. Cleanliness is the key

Always touch your healthy plants with disinfected hands and gloves.  If possible, disinfect your shoes and then take a walk in your garden.

Burn all the infected plants and leaves in a burn pile away from the garden.

After every use, disinfect your cultivars, scissors, clippers, and other equipment in a bleach solution. 

Check out this video for preventions of leaf spot-

Remove all the plant residues from your garden regularly.

  • Avoid crowding of the tomato plants.
  • Take proper care of the plants in the rainy season.
  • Promote good air circulation between the plants and in the plants.
  • Staking, Mulching, and pruning your tomato plants will enhance air circulation, maintain the required distance between soil and plant, provide organic nutrients to plants; and provide physical support to the plant. 
  • Plant your tomatoes in raised beds or in containers. This will reduce the risk of infection from infected plant residues. 

Check out this video on staking, pruning and mulching tomato plants –

FAQ’s

Which resistant gene is isolated from wild tomato species?

Sm, the resistant gene is isolated from tomato species and is found to be effective against Stemphylium gray leaf spot.

Can tomato fruits recover from Stemphylium gray leaf spots?

Stemphylium gray leaf spot affects leaves of the tomato plant. It does not directly infect the tomato fruits. 

Are tomatoes infected with Stemphylium gray leaf spot edible?

Yes, you can definitely eat tomatoes infected with leaf spot. Stemphylium does not cause any harm to fruits.

Should I water my plants in the evening?

No, you should water your plants in the morning as it will give your plants sufficient hours of sunlight to facilitate the drying of the foliage. 

Summary

I hope that this quick guide on the Stemphylium gray leaf spot of the tomato plant will help you prevent/manage it in your garden

Suggestions and feedbacks are always welcome. 

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