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Tomato diseases

 Understanding tomato diseases: early detection and preventive measures 

This section is continually updated and supplemented. 

Late blight and brown blight

Late blight and brown blight are two widespread fungal diseases that primarily affect plants such as tomatoes, potatoes and other nightshades. These diseases can have devastating effects on crops and are a nightmare for gardeners. In this article, I take a closer look at late blight, its causes, symptoms, and the best methods to combat these dreaded plant diseases. 

Weed and brown rot in the early stages

Early blight and brown blight


  • Stems develop brown spots

Brown and late blight on the entire plant in the final stage

Late blight and brown blight


  • The plants and fruits can no longer be saved. Everything turns brown

Brown rot spread to the fruits

Late blight and brown rot can be seen on the fruits


  • Fruits get brown spots

Main causes of the spread of late blight

  1. Humid weather: Rain and high humidity create ideal conditions for the growth and spread of these fungi.

  2. Inadequate ventilation: Plants grown in tight, poorly ventilated areas are more susceptible to infection.

  3. Contaminated soil: The fungus can overwinter in the soil and be transmitted to plants from year to year.

Symptoms of late blight vary depending on the plant species and stage of infection. Here are the most common signs:

  1. Late blight (Phytophthora infestans):

    • First, dark, water-soaked spots appear on the leaves, which quickly become brownish lesions (Image 1 above; initial stage)

    • The leaves wilt and die, often starting on the lower parts of the plant.

    • A characteristic smell of decay may occur.

  2. Brown rot (Phytophthora capsici):

    • Brownish spots initially appear on the fruit, which quickly spread.

    • The fruits may shrivel, shrivel and eventually rot (Image 3 above; final stage)

Symptoms of late blight and brown blight


Combat in general

Combating late blight requires a combination of preventative measures and targeted interventions as soon as the disease occurs:

  1. Prevention:

    • Choose resistant varieties: There are some varieties of plants that have natural resistance to late blight. These are e.g. b. most wild varieties such as microberry, currant tomato or tindindogo. But Sunviva is also one of the resistant varieties.

    • Improve ventilation: It is important to ensure that plants have enough space and are well ventilated.

    • Avoiding soggy tomato foliage: It is best to only water the plants in the morning to ensure the foliage stays dry until night.

    • Avoid contaminated soil: You should change the location of nightshade plants every year of cultivation.

  2. Intervention:

    • Removing infected material: As soon as you notice the symptoms, you should immediately remove the infected parts of the plants to prevent spread.

    • Early harvest: If the disease has already emerged, early harvesting of fruits can minimize losses in some cases.

Fighting with biological means

Fighting late blight with biological means is more environmentally friendly and can represent a sustainable alternative to chemical pesticides. Here are some biological agents and methods that can be used to treat and prevent late blight:


  • Biological fungicides: There are biological fungicides based on beneficial microorganisms such as Bacillus subtilis, Trichoderma or Streptomyces that can help combat fungal infections. These beneficial bacteria and fungi compete with pathogens for resources or produce antibacterial compounds.


  • Copper-free products: Some manufacturers offer copper-free fungicides that are based on natural active ingredients such as potassium bicarbonate or sulfur. These are less harmful to the environment than copper-based preparations.


  • Cradle cap preparations: Cradle cap preparations based on diluted milk or whey can be used as a preventative measure against late blight and brown rot. They form a protective layer on the leaves, preventing fungal spores from adhering.


  • silica: Silica can strengthen plant tissue and make the plant more resistant to disease. It can be applied as a foliar spray or soil fertilizer.


  • Neem-based plant protection products: Neem oil is extracted from the seeds of the neem tree and has insecticidal and fungicidal properties. It can be used as a foliar spray to combat fungal infections.


  • Garlic and onion extracts: Garlic and onion extracts have natural fungicidal properties and can be used as sprays.


  • Promote biological diversity: By promoting biodiversity in your garden, natural enemies of pathogens, such as ladybugs or predatory mites, can help keep pathogen populations in check.


It is important to note that biological agents may not always work as quickly and effectively as chemical pesticides. Use should be regular and preventative to achieve the best results. Combine different biological approaches and pay attention to the application instructions to maximize effectiveness while protecting the environment.

Time of application of the biological agents

The use of biological agents to combat late blight should be carried out preventively before the disease actually occurs. These fungal diseases are often difficult to treat once established. Here are some guidelines for when and how to use biologicals most effectively:

  • Apply early: The application of biological agents should begin in the early stages of plant growth, ideally when the plants are still healthy and show no signs of late blight or brown rot. This is usually when the plants have just been sown or planted.


  • Continuous application: Many biological agents offer limited protection and must be used regularly, especially during wet or rainy periods. Check the instructions on the product and follow the recommended application interval.


  • Repeated applications: Note that biological agents are usually not as strong as chemical pesticides. Therefore, it may be necessary to repeat the application several times to achieve the desired effect.


  • Early observation: Monitor your plants carefully for signs of pathogens. If you notice even minor signs of late blight or brown rot, you should take immediate action, for example by removing affected parts of the plant and increasing the use of biological agents.


  • Preventive action: In addition to using biological agents, you should also take preventive measures such as choosing resistant plant varieties, creating good ventilation and avoiding contaminated soil.


  • Pay attention to weather conditions: Late blight and brown blight spread particularly in wet and rainy periods. During these times you should be particularly vigilant and increase the use of biological agents.


  • Encourage natural enemies: Promoting biodiversity in your garden can help attract natural enemies of pathogens, thereby limiting the spread of late blight.


Please remember that organic agents are often a more sustainable option, but they typically require more patience and attention compared to chemical pesticides.


However, timely and continuous application of biological agents can help reduce the likelihood of late blight infestation in the garden.

Blossom end rot

Blossom end rot is a common physiological disorder that occurs in tomatoes.

Tomato Mila blossom end rot
Blossom end rot tomato drape

Blossom end rot is relatively easy to spot.

Typical signs aretan,putrid stainswho are at thebottomof the tomato fruit, usually near the base of the flower. These spots start small and can expand over time

increase time, which makes the fruit inedible.

Main cause of blossom end rot

The main cause of blossom end rot in tomatoes is a calcium deficiency in the fruit. Calcium is an essential nutrient for the growth and development of tomatoes. If the plant cannot absorb enough calcium, this undesirable phenomenon occurs. Calcium deficiency can occur due to several factors:

  1. Fluctuating temperatures: Tomato plants are sensitive to temperature changes. If temperatures vary greatly, especially during the growth phase, the plant's calcium absorption can be affected.

  2. Irregular watering: A consistent moisture content is crucial for the absorption of calcium by the roots. Irregular watering or prolonged dry periods can lead to calcium deficiency.

  3. Irregular fertilization: Proper fertilization with required nutrients, including calcium, is important. If fertilization is irregular or does not meet the needs of the plant, this can lead to calcium deficiency.

Prevention and what to do after discovering affected fruit

The good news is that blossom end rot can be prevented in most cases. Here are some preventive measures:

  1. Ensuring adequate calcium supply: Use calcium-rich fertilizers or lime to ensure tomato plants receive adequate calcium.

  2. Consistent watering: One should ensure that the plants are watered regularly and evenly to help the absorption of calcium by the roots.

  3. Controlling temperature fluctuations: If possible, you should protect tomato plants from strong temperature fluctuations, for example by using mulch or shading.

  4. Early detection: Inspect fruit regularly for signs of blossom end rot so that early action can be taken.

What to do with affected tomatoes?

Tomatoes affected by blossom end rot do not necessarily have to be thrown away. Here it is sufficient to use the sCut off damaged areas generously and dispose of them. The rest of the tomato (if there is enough left) can be eaten safely.


Blossom end rot may be similarbe annoying, but it doesn't necessarily mean the end of the tomato harvest. With proper handling, most affected tomatoes can be saved.

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