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Tomato blight is a class of fungus that lodges as a parasite in different cereals and plants. Alternaria solani is part of these fungi and causes the disease called early blight in tomatoes. This fungus generates spots on the stems and leaves, causing damage that ends up rotting the tuber. Phytophthora infestans, for its part, generate late blight. It is a pest that can destroy tomatoes, potatoes, and other crops intended for human consumption.

Symptoms of Tomato Blight

Tomatoes with late blight symptoms

When checking plants for blight, pay attention to symptoms to positively identify the disease. Although the treatment for all types of blight is the same, the symptoms are slightly different.

Early Blight – Early blight is a disease that puts the cultivation of the tomato plant at risk like few others since it can appear at any stage of its growth and affect all its aerial organs, from its stem to its leaves and, of course, its fruits. It is a danger that farmers must be aware of and combat throughout development.

Early-acting blight symptoms usually begin after the first fruits appear on tomato plants, beginning with a few small, brown lesions on the underside of the leaves. As the lesions increase, they take the form of rings like those of a shooting target and show dry and dead tissue in the center. The surrounding plant tissue turns yellow and then brown before the leaves die off the plant. Although early-acting blight does not affect fruit directly, loss of protective foliage can cause fruit damage due to direct exposure to sunlight. This condition is known as sunburn.

Late Blight – Late blight is one of those that cause the greatest destruction to plants, partly because of its speed to travel through the air but also because of its great reproductive capacity and because of the characteristics of the fungus that generates it, which is highly virulent. Furthermore, almost no aerial tissue on a plant affected by late blight has a very good chance of escaping its effects.

Late-acting blight can affect tomato plants at any point in the growing season. Symptoms appear on the edge of tomato leaves and show dark, damaged tissues that spread down the leaves to the stem. White mold may grow on the underside of the leaf in the affected area. This type of blight develops rapidly on plants in humid conditions and, if measures are not taken in time, it can spread towards the fruits.

 This disease can be devastating, particularly under favorable conditions, since the causative pathogen can produce large quantities of spores that are dispersed with the wind and continue their life cycle very quickly; advancing from infection to a new lesion or spot will produce new spores in 6 or 7 days.

Septoria – As with early-acting blight, the first symptoms of septoria often begin on the lower leaves of the plant after the fruits have emerged. Instead of manifesting as a few lesions per leaf, septoria appears as many small brown spots on the leaves. Lesions continue to spread and grow before causing leaf drop. This type of blight usually does not affect the fruits.

Prevention

Avoid growing tomatos in a high humidity greenhouse to avoid tomato blight

These are some tips to prevent any type of blight in your tomato crops:

  • Remove crop residues, weeds, and spontaneous plants.
  • Use clean seeds and propagating materials.
  • Practice crop rotation, especially when spores that survive in the soil are the main cause of infection.
  • Use blight-resistant varieties.
  • Postharvest storage at 0-1 ° C.
  • In greenhouses: avoid high relative humidity.

Prevent diseases in plants by optimizing their potential, as well as the resilience of the crop.

Blight Control

Tomato 'blight control' with 4 images of leaves and tomatos
  • Use transplants produced in an area where the blight has not been developing on plants, inside or outside the greenhouse.
  • Select resistant varieties. There are tomato varieties on the market with resistance to late blight, some of them supplemented with resistance to early blight and Septoriosis or tomato leaf pox.
  • Control spontaneous plants, as well as weeds of the nightshade family
  • Regularly inspect your crops for blight symptoms.
  • Consult your extension agency or local government to find out about the occurrence of tomato blight in your area
  • Apply copper fungicides regularly in a preventive way, as long as there is a risk of late blight
  • Observe your cultivation. If tomato blight symptoms are seen in isolated areas of the field, it is possible to save the crop. Success depends on how early symptoms are detected.
  • It is advisable to remove the tissue from the affected plant immediately, preferably on a sunny day when there are fewer spores, and the leaves are dry.
  • Inspect the plants daily for a week for infected plants that have developed symptoms, and return to inspect at least once a week.
  • Work in the affected fields last. Clean equipment between field and field.
  • Destroy foliage when tomato blight is severe. This eliminates plants that can serve as a source of spores for other plants in your operation or the vicinity.
  • Deposit the affected tissue in bags and bury them, or deposit them in a pile and cover them with canvas. The heat from the incident solar radiation will quickly kill the tissue and the pathogen.
  •  Keep an eye on the fruits, since if they come from an affected field, they could develop symptoms after harvest and therefore should be inspected before being marketed.
  • Damage from early blight cannot occur unless the fungi jump out of the ground onto the leaves and stems; this is why a layer of mulch around the base of the plants helps keep the soil covered and prevent splashing water.

Always read product labels and follow directions, including directions on which plants you can treat and pre-harvest intervals (PHI) for edible crops.

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