Gardening News & Tips

Tomato Blight

When plants suffer from tomato blight, leaves suddenly wither, stop growing, and die. Later, plant parts may rot.

Infectious plant diseases are often classified by the type of symptom they cause.Common diseases include early and late blights that are caused by fungi and attack tomatoes and their relatives.

Causes

If leaves of your tomato plants have dark, ringed spots, the cause may be early blight. Lower leaves and stems are generally affected first by tomato blight. This fungal disease is also known as Alternaria blight. The disease occurs when plants are loaded with fruit and during warm, humid temperatures of 75 to 85 degrees.

Late tomato blight often causes foliage with water-soaked patches that turn brown, dry, and papery. In wet weather the patches may develop a ring of white mold. Additionally, stems may have blackened areas. Infected fruit have large, firm, greasy, irregular brown spots. This fungal disease frequently occurs during humid weather with cool nights below 60 degrees and warm days of 70 to 85 degrees.

Other indications of tomato blight:

Fruit with green, water soaked spots is often caused by late blight. Spots expand into large brown areas but remain firm. Spots that appear near the stem while fruit is green are symptoms of early blight.

Best organic control

For early and late tomato blight: Spray infected plants with sulfur and/or copper to halt further blight development. Sulfur is one of the oldest pesticides known. It has been used for centuries to control plant pathogens like blight. Sulfur is mined from natural deposits as a yellow solid that is nearly soluble in water. It is available in solution form or as a finely ground dust.

Horsetail Spray

Some organic gardeners use the common weed horsetail spray as a botanical fungicide to prevent and control plant diseases such as tomato blight. Although, the spray has not been scientifically tested for fungicidal properties, it is popular among backyard gardeners as a protectant fungicide.

Spray infected plants once every week to 2 weeks. Sometimes a fungal disease outbreak can be anticipated due to forecasted and current weather conditions. It is good advice to begin a preventive spray routine before any symptoms are even spotted. Experiment to determine which plants and diseases the spray works best on and keep records for future reference.

Non-organic methods

Sulfur can be mixed with inorganic fungicides to use as a protectant fungicide against blight, powdery mildews, rusts, and other plant diseases effecting tomatoes.

Precautions

Even though sulfur is probably the most commonly used organic fungicide, it is moderately toxic to humans and other mammals. Use carefully or it can irritate lungs, skin, or eyes. Always wear protective clothing when applying sulfur.

Prevention

By selecting a well-drained, uphill gardening site, you can reduce the time your plant leaves remain wet from rain or watering. Choosing a bed that is basking in sunlight and gentle breezes can keep your plants high and dry. Pruning helps air to circulate freely among the plants allowing the sunshine to rapidly dry foliage and branches after the morning dew or seasonal rains. Crop rotation can stamp out soil borne pathogens.

Prevent problems of tomato blight by planting resistant cultivars and spraying transplants with an anti-transpirant. Although they are usually not thought of as fungicides, anti-transpirants and oil sprays may help prevent fungal infections. Both of these products form a coating on leaves that seems to prevent spore germination and penetration. For late blights: Spray plants with compost tea to help avoid further symptoms from developing.

Go to Identifying-Garden-Pests from Tomato Blight