Are you trying to cure tomato blight to save your crop? Tomatoes (Lycopersicum esculentum, USDA zones 10-11) are grown as annuals in most American vegetable gardens for eating and cooking. While they're relatively hardy and easy to grow, they are susceptible to different types of of blight. A number of treatments can destroy and prevent blight. Prior to treatment, fruit showing signs of blight infection should not be eaten or used for canning.
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Types of Tomato Blight
There are different types of blight that attack garden-grown tomatoes. Early blight is cause by different fungal pathogens, notably Alternaria solani and Alternaria tomatophila. It causes brown wounds on foliage, stems and fruit. The wounds grow and can damage an entire tomato fruit. Wounds frequently develop into a bulls-eye type spot. Tomatoes eventually drop from the stems. The fungus lives in debris and soil under the plants and benefits from moist conditions.
Late blight develops within 14 days of a tomato plant contracting the fungus Phytophthora infestans. Symptoms include browning and shriveling leaves and stems. In addition, dark, water-soaked lesions appear on leaves that develop into spots with white mold edges. Fruits have dark lesions that can grow across broad areas. This fungus spreads through rain and wind. Late blight flourishes in cool, wet conditions.
Southern blight is caused by the fungal pathogen Sclerotium rolfsii. This fungus rots stems near the soil line and wilts leaves. The brown rot is comprised of lesions that often have a white fungal covering. Southern blight can damage fruits that touch the soil. The fungus can live in soil and plant debris for years. It prefers moist, hot conditions.
Homemade Fungicide and Myths
Homemade fungicidal concoctions (some of which call for mixing cooking oil, baby shampoo, and baking soda in water) are anecdotal and not backed by scientific research. While you made have heard the rumor that a copper wire inserted into a tomato stem prevents blight, there's no evidence proving that remedy. Home remedy rumors suggesting bleach to cure tomato blight are also unfounded. Bleach damages gardening tools, plant tissues, plant seeds and clothing, and it can also cause human health issues.
Some gardeners apply cornmeal to the soil or create a cornmeal spray to prevent blight. Cornmeal is often used in scientific and university labs to grow fungi, so it certainly is not a fungicide. Cornmeal cannot prevent or cure tomato blight.
Commercial Fungicide Products
Manage tomato blight infections by using a synthetic or organic fungicide. Although fungicides are effective as preventives (before a disease takes hold), they have limited effectiveness as curatives (after a disease takes hold). You'll need to reapply fungicides every three or seven to 10 days, according to label directions.
Gardeners can treat tomato plants with fungicide from two to five days before harvesting fruit, depending on label-specific recommendations. Keep children and pets away when treating plants.
Repairing Soil and Preventing Blight
A number of measures may prevent blight:
- Water plants at the soil level to keep foliage dry.
- Space plants so they do not touch.
- Use only disease-free plants and seeds.
- Mulch under plants to keep soilborne pathogens from splashing onto the plants.
- Practice crop rotation by waiting three years to plant tomatoes in the same area where any tomatoes or other solanaceous crops, such as peppers, eggplants, and tomatoes, have been grown.
- Remove plants and underlying debris after the final harvest.
- Choose blight-resistant cultivars.
- Remove any nearby potato plants and weeds.
- Avoid composting potatoes that are rotten or purchased at a store.