Late blight is among the most destructive fungal diseases of tomatoes. It spreads fast when not controlled. The damage caused by the disease can be significant, especially when the right conditions for the spread are made available: a moist and cool environment. To prevent the heartaches of treating this disease, it is best for any organic gardener to understand the causes, symptoms, and most effective organic treatments.
Quick fact
While Late blight was first discovered in the US in 1840, it was only first discovered in 2018 in Iraq, First record of tomato late blight in Basrah province. Read here
What Is Late Blight in Tomatoes?
Late blight is a dangerous fungal disease caused by the fungus Phytophthora infestans which thrives in moist environments. Black lesions appear on the stems of the infected tomato. The fruit from the infected tomato tree appears dark and greasy. If not detected and treated early, late blight can spread so quickly and destroy the plant.
Symptoms of Late Blight in Tomatoes
It is very easy to identify late blight in tomatoes since its symptoms are well visible. Late blight normally affects the leaves, stems, and/or fruits of the tomato plant. Early detection of this disease will help prevent further spread of the disease and safe your crop. The following are the most common symptoms of Late blight in tomatoes.
1. Leaf Lesions
- The most noticeable symptom of late blight is the appearance of dark, water-soaked lesions on the lower leaves of the plant. These lesions typically have irregular, angular shapes.
- As the disease progresses, the lesions enlarge and turn dark brown or black, often with a white, fuzzy mold visible on the underside of the leaves, especially in humid conditions.
2. Stem Rot
- The lesions on stems may appear as brown or black streaks. The stem can rot, leading to the collapse of affected plants. This is most common during advanced stages of the disease.
3. Fruit Damage
- Late blight also affects the fruit, causing dark, sunken lesions that may appear water-soaked and eventually turn brown. Infected fruit may rot quickly, often before it is fully ripe.
- Infected fruit can become soft and mushy, leading to significant crop loss.
4. Premature Plant Death
- In severe cases, late blight causes widespread defoliation, which weakens the plant and reduces its ability to photosynthesize. This leads to premature plant death.
5. White Mold Growth
- During wet conditions, white, fluffy mold growth (spores) often appears on the underside of affected leaves and stems, which is a clear sign of late blight infection.
Organic Treatment for Late Blight in Tomatoes
While late blight can spread quickly and devastate your tomato crop, there are several organic methods to help prevent and control this disease. Here are some of the most effective organic treatments for late blight in tomatoes:
1. Remove and Destroy Infected Plant Material
- As soon as you notice symptoms of late blight, remove infected leaves, stems, and fruit to reduce the spread of spores. Be sure to destroy the infected plant material by burning or disposing of it in a sealed bag. Do not compost infected material, as the spores can survive and spread to other plants.
2. Improve Air Circulation
- Proper spacing and pruning of your tomato plants can help improve airflow around the plants. This reduces humidity around the foliage and makes it less conducive for the growth of the pathogen. Prune any dead or damaged leaves, and avoid overcrowding your plants to ensure good air circulation.
3. Use Organic Fungicides
- There are several organic fungicides that can help prevent or slow the spread of late blight:
- Copper-based fungicides: These are commonly used for controlling late blight. They work by disrupting the cell structure of the pathogen.
- Neem oil: Neem oil is a broad-spectrum pesticide and fungicide that can help control late blight when applied regularly.
- Sulfur: Sulfur-based fungicides can also be used to protect tomatoes from late blight. It is effective at killing fungal spores on the surface of plants.
- Baking soda solution: A mixture of baking soda and water can act as a preventive measure. It works by altering the pH of the plant surface, creating an unfavorable environment for the pathogen.
4. Apply Biological Controls
- Some biological agents can help reduce late blight infections:
- Trichoderma spp.: This beneficial fungus can be applied to soil and plant surfaces to help suppress the growth of pathogens like Phytophthora infestans.
- Bacillus subtilis: A bacteria-based biological control agent, Bacillus subtilis can help to suppress fungal growth on tomato plants.
5. Crop Rotation
- Practice crop rotation by planting tomatoes in a different location each year. Avoid planting tomatoes or other solanaceous crops (e.g., peppers, potatoes) in the same soil for at least two years to reduce the buildup of fungal spores in the soil.
6. Watering Practices
- Water your tomato plants at the base rather than overhead to avoid wetting the leaves. This reduces the opportunity for spores to spread and infect the foliage. Water early in the day to allow the plants to dry before evening, reducing moisture on the leaves overnight.
7. Resistant Varieties
- If late blight is a recurring problem in your area, consider planting late blight-resistant tomato varieties. These varieties have been bred to resist infection from Phytophthora infestans and can significantly reduce the risk of the disease.
8. Mulching
- Apply organic mulch around the base of your tomato plants to help keep soil moisture levels consistent and prevent water splashing onto the lower leaves, which can spread the pathogen.
Conclusion
Late blight is a serious and fast-spreading disease that can devastate tomato crops if not managed properly. Recognizing the symptoms early and implementing organic control methods, such as removing infected plant material, improving air circulation, and using organic fungicides, can help mitigate the damage caused by late blight. By practicing good gardening practices like crop rotation, proper watering, and choosing resistant varieties, you can minimize the risk of late blight and ensure healthy, productive tomato plants. With vigilance and appropriate organic treatments, you can successfully combat this destructive disease and protect your tomato harvest.
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