Early Blight is a plant disease that affects tomato and potato crops, causing significant damage and reducing yield. Alternaria solani is the fungus that causes this disease. It is prevalent in many regions, including Minnesota, where it occurs in nearly every growing season. Early Blight infects the plant’s leaves, stems, and fruits, leading to severe defoliation and damage to the fruit.
The fruit can become sunburned in tomatoes due to the loss of leaves. This disease can be devastating for farmers as it can significantly impact their yields, especially when susceptible cultivars are used and weather conditions are favorable for the disease to spread.
Early Blight Management in Tomato
The Disease Cycle of Early Blight
The life cycle of early Blight of tomato, caused by the fungus Alternaria solani, can be divided into the following stages:
- Spore Production: The fungus produces spores on infected leaves and flowers, which release spores into the air and spread the disease to healthy plants.
- Germination: The spores come into contact with a suitable host, typically tomato leaves, and germinate in the presence of moisture.
- Penetration: The fungal hyphae penetrate the tomato plant through wounds or stomata, the tiny pores in leaves through which they exchange gases.
- Establishment of Infection: Once inside the plant, the fungus begins to colonize the tissues, causing the plant to weaken and produce the characteristic dark, circular leaf lesions.
- Sporulation: The fungus continues to grow, producing more spores and spreading the infection to other parts of the plant and other plants nearby.
- Repeat Cycle: The cycle of infection, sporulation, and spread continues, potentially leading to significant damage to the tomato crop and reducing yield.
The Causal Organism of Early Blight
- The causal organism of Early Blight is Alternaria solani and Alternaria tomatophila. These two species are closely related and are capable of causing early Blight in tomato plants.
- They can overwinter in infected plant debris and soil and survive on tomato seed or be introduced to tomato transplants, which can help them spread from one location to another.
Damage Symptoms of Early Blight in Tomato Field
- Leaf damage: The first signs of the disease appear as small black or brown lesions on the leaves, which can enlarge to 10 mm or more in diameter with characteristic concentric rings. As the disease progresses, the entire leaves may turn yellow and fall off, resulting in significant defoliation.
- Stem damage: Lesions on the stems are often lens-shaped with a light center and the same concentric rings seen on the leaves. On young seedlings, the stem lesions may completely girdle the stem, causing reduced plant vigor or death.
- Fruit damage: The fruit can also be affected by Early Blight, with black or brown spots or scabs on the skin. Sunburn can occur on exposed fruit due to the loss of leaves, further reducing the marketability of the fruit.
- Reduced plant vigor: Early Blight can cause significant defoliation, reducing the plant’s ability to photosynthesize and reducing plant vigor. This, in turn, can negatively impact yield and fruit quality.
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Early Blight Management in Tomato by Cultural Method
- Use tolerant or resistant varieties: Choose tomato varieties that are tolerant or resistant to early Blight, such as ‘Floradade,’ ‘Hytec 36’, ‘Julius F1’, ‘Rio Grande,’ ‘Rossol,’ ‘Summerset F1’, ‘Zeal F1’, and ‘Zest F1’.
- Destroy crop debris after harvest: Remove all crop residues and infected material, and burn or dispose of it properly. This will help to physically remove the inoculum from the topsoil and reduce the spread of early Blight.
- Crop rotation: Implement a crop rotation plan that avoids planting tomatoes, Irish potatoes, or eggplant for at least two cropping seasons, as these plants are hosts for early Blight. Rotate crops with small grains, maize, or legumes to reduce disease risk.
Early Blight Management in Tomato by Biological Method
- Biological control is a method of managing early Blight in tomatoes that uses natural predators and pathogens to control the growth and spread of the disease-causing fungus. One such biological control agent is Bacillus subtilis (BS-01).
- BS-01 is a naturally occurring bacterium that has been found to have antifungal properties against a number of plant pathogens, including the early blight-causing fungus Alternaria solani. BS-01 can be applied to tomato plants as a microbial suspension in a solution of ice-cold phosphate-buffered saline.
- Applying BS-01 to tomato plants can help prevent early blight establishment by competing with the pathogenic fungus for nutrients and space on the plant surface. In addition, BS-01 has been shown to produce antifungal compounds that can directly inhibit the growth of Alternaria solani.
Early Blight Management in Tomato by The Chemical Method
Early Blight management in tomatoes can be effectively managed by using chemical fungicides. The following fungicides were used in the study:
- Oxy plus 28.5% WP Copper hydroxide (inorganic fungicide)
- Ridomil Gold MZ 68% WP (manganese and zinc ethylenbisdithiocarbamate and N-(2,6-dimethylphenyl) N-(methoxyacytel)-DL-alanine methyl ester)
- Shirlan 50% SC Fluazinam (2,6-dinitroaniline)
- Dolphin Alfa 25% EC Difenoconazole (triazole compound)
- Ranman 40% SC Cyanoimidazole (cyanoimidazole)
- Revus 25% SC Mndipropamid (mandelamide)
- Flint 50% WG Trifloxystrobin (strbilurin compounds)
- Amisulbrom 20% SC Sulfonamide (unclassified)
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Preventive Measures for Control of Early Blight
- Sanitation: Remove all crop residues, weeds, and volunteer plants to reduce the presence of the fungal pathogen.
- Proper storage: Store crops at 0-1oC post-harvest to reduce disease risk.
- Greenhouse conditions: In greenhouses, maintain low relative humidity to reduce the risk of infection.
- Plant health: Optimize plant potential and crop resilience by promoting good plant health and reducing disease risk.
- Monitoring: Regularly monitor crops for signs of early Blight and take prompt action if necessary.
Conclusion
Early Blight is a destructive disease that can cause significant damage to tomato crops, including leaf and stem lesions, fruit damage, and reduced plant vigor. It is essential to implement effective control measures to prevent the spread of this disease and reduce its impact on tomato production.
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