Late Blight of Tomato Plant: Identification, Control & Prevention

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Quick Answer: Late Blight of Tomato Plant

Tomato plants are inclined to develop Late Blight disease in a humid climate. Late Blight disease occurs late in the season and shows early symptoms like wet spots on leaflets that eventually become brown and necrotic. Late blight disease worsens when tomato plants are cultivated in moisture-containing environments. Late Blight disease is a constant and serious threat that needs to get prevented by preventative fungicides and should be managed by adopting simple gardening tips.

This is a detailed guide on the Blight Disease of tomato plants.

What is Tomato Late Blight Disease?

Late Blight fungi P. infestans is also called ‘ Plant destroyer’. It can affect the tomato plant at any stage of its growth. It affects tomato seedlings as well. P. infestans takes 5 to 10 days to spread infection in the whole plant and can survive as spores for weeks. 

Tomato Late Blight disease develops from oomycetes [water molds] of Phytophthora infestans. These fungi go through both asexual and sexual life cycles and have a high evolutionary rate. 

Late Blight survives in plant debris for weeks as oospores. These oospores enter in next stage of their asexual cycle under 91-100% humidity,   optimum temperature range of approximately 64–79°F.

Cool and wet weather, high humidity, and crowded tomato plants favor the spreading of late blight disease.

However, the dispersal of the oomycetes of P.infestans is through wind, water, and human contact. 

Late Blight infects all aerial plants of tomato plants. It displays its first sign on leaves, branches, and then fruits. Late blight spreads rapidly. It causes leaves to dry and, later, leaves fall off.

How Late Blight Infects Tomato Plants?

The Late Blight pathogen undergoes both cycles: Asexual and Sexual. 

The germination of sporangium on a tomato plant occurs through abiotic factors- wind and water; and biotic factors- human contact. The source of these spores is infected parts of the tomato plant. 

A temperature of 25◦ C is suitable for the process of germination on the tomato plant. 

Infection develops after 10 hours of inoculation [spores landing on the tomato plant]. Later, it disperses to petioles and fruits of the tomato plant. It takes 5-10 days for the tomato plant to die completely from Late blight disease.

These spores infect the bottom side of the tomato plant first as it is in close contact with the ground. It then infects the stem region and, later, the fruits of the tomato plant.

The extent and rate of infection spread depend entirely on environmental conditions and management tips of the tomato plant. 

Late Blight is not a soil-borne disease but develops from infected tubers and plants and disperses through various mechanisms. Cooler and wet temperature; high humidity favors its rapid spread. 

The spores of late blight remain in sporangia form for weeks and, thus, become the most destructive threat to the tomato plant.  

How to Confirm that Late Blight is Troubling your Tomato Plants?

Here are the key symptoms of Late Blight on various parts of the tomato plant –

1. Leaf

The early symptoms of Late Blight disease appear on the leaves of the tomato plant. The bottom leaves, which are in contact with the bottom, develop the infection and spread it throughout the plant. 

The symptoms that distinguish Late Blight from any other Disease are-

  • Development of wet spots or patches on leaflets.
  • Purple, dark brown, or black water-soaked lesions.
  •  White growth is found on the undersides of leaves due to the development of sporangiophores or sporangia. 
  • Lesions on the lower side of the leaflet appear greasy due to wet weather. 

During the later stage of Late Blight disease, the foliage turns brown, then the leaf curls get dry, and die. 

White cottony growth on black lesions due to wetting of leaves
  Curling of leaflets due to Late Blight Disease

2. Stem

Late blight first infects tender parts of the stem and then advances to older and woody parts of the stem. However, the infection progresses slowly on woody parts but develops rather prominent symptoms. The lesions of the stem might appear as –

  • Firm and dark with a rounded edge. 
  • Greasy lesions.
  • These lesions first appear at the node and then at the bottom of the stem.
  • Grey lesion with white cottony growth due to extreme wet weather.
 Infected stem [Dark brown lesions]

Check out this video to find out more about Late Blight Disease symptoms in Tomato plants-

Ways to Control Late blight Disease on Tomato Plants

Late Blight disease is a fast-spreading disease and, thus, needs to get controlled before all your tomato plants die. 

1. Preventative Fungicides

Scientists suggest using Actinovate as a preventative spray and adding a copper-based product when late blight is present.

Products containing chlorothalonil [known as ‘Daconil’] are the best and only effective products available to home gardeners. 

FAMOXADONE + CYMOXANIL is a famous combination of chemicals to fight against the late blight disease of the tomato plant.

The spraying of any fungicide should be strictly according to the instructions given on the label. The quantity of fungicide, duration of spray, and ingredients should be looked at before the application.

It is advised to spray fungicides weekly during the growing season.

Check out this video for preparation of home fungicide-

  • Stake up or cage up your tomato plants. Keep tomato stems and branches away from the ground. Maintain a distance of one hand between the ground and the plant. 
  • Mulch your plants with organic matter to enhance soil quality and reduce the risk of water splashing.
  • Water your plant through manually constructed trenches. This will ensure that the water reaches just the roots and will avoid the wetting of foliage.

Check out this video on how to do pruning and Staking-

Using Resistant Tomato Varieties – 

It is best to look for resistant tomato seeds. The most effective method for controlling the Late blight of the tomato plant is by planting seeds that resist it. 

 Major gene resistance gives protection against one genotype only and might be proven a good choice for late blight disease.

For late blight, there are four major gene resistance- Ph-1, Ph-2, Ph-3, and Ph-5. The type of resistant variety chosen should be based on these four major genes.

Planting resistant variety seeds with uniform spraying of fungicides on the tomato plants since the beginning of their growing season helps control the late blight of tomato disease.

3. Better Site Selection for Tomato Planting

Environmental and soil conditions play a significant role in the development of the disease. You should always choose a site that has-

  • Pre-sterilized soil.
  • Less moisture content in the air.
  • Dry climate.
  • Availability and excess to fungicides.
  • Less shaded trees.

How to Prevent Late Blight on Tomato Plants?

There is no way we can ensure the protection of our tomato plants from late blight but taking much-needed steps to take care of tomato plants might at least reduce the risk of death due to late blight. 

  • Do not cultivate your tomatoes in blight-prone seasons or months.
  • Keep a tab on weather conditions.
  • Keep regular checks on plants. Remove weeds or infected regions as soon as possible. Always either burn the infected ones or pack them in a zip lock sealed bag.
  • Disinfect your hands and other gardening tools on a regular basis.
  • Do not compost your dead foliage, stems, or fruits.  
  • Provide adequate plant nutrition through silica-containing fertilizers. 
  • Avoid overcrowding of your plants. This will ensure proper air circulation and minimize the risk of exposing the plant to moisture.
  • Avoid moving through the tomato garden when plant leaves are wet.
  • Water your plants during the daytime so that they get enough time to get dry. 
  • Make sure you water only the roots of the tomato plant very gently.
  • Harvest tomatoes as soon as possible, even if they are green and not ripened. 

Check out this video for preventing late blight development-


Can tomatoes recover from late blight?

No, there are very few chances that your plant will recover from Late blight. However, you can manage the disease and can prevent the further spreading of infection. 

Can Late blight survive in soil?

Late blight neither lives in soil nor can survive in soil. It overwinters in soil and disperses through wind, water, and human contact.  

What is the difference between Early Blight and Late Blight?

The lesions of Early blight are sunken and brown. 
In late blight, lesions are brown, purple, and yellow and have a white cottony layer due to frost and wet conditions. 

Why is the Late Blight disease of the tomato Plant so dangerous?

Tomato Late blight disease is a communicable disease. The pathogen of Late blight disease is declared as fungi with high evolutionary potential so, there are no techniques that can resist its development. 


I hope this guide has provided you with some valuable tips on identification, managing, and preventing Late Blight disease on the tomato plant.

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