Blight On Tomatoes – Tomato Blight Treatment And Prevention

Tomato Blight 2010
Image by Tony Austin

By Jackie Rhoades

What is tomato blight? Blight on tomatoes is caused by a fungal infection and like all fungi; they are spread by spores and require damp, warm weather conditions to flourish.

What is Tomato Blight?

What is tomato blight? It’s actually three different fungi that attack tomatoes in three different ways at three different times.

Septoria blight, also called leaf spot, is the most common blight on tomatoes. It usually appears at the end of July with small black or brown marks on the lower leaves. While fruits may remain uninfected, the leaf loss can affect yield as well as exposing fruit to sunscald. Overall, it is the least harmful tomato blight. Solutions to the problem include watering at the base of plants and avoiding the garden while foliage is wet.

Early blight appears after heavy fruit set. Rings resembling targets develop first on the leaves and cankers soon grow on the stems. Black spots on the almost ripened fruit turn into large bruised spots and the fruit begins to fall. Because the crop is almost ready for picking, this may be the most disappointing tomato blight. Treatment is simple. To prevent tomato blight from invading next year’s crop, burn everything the fungus may have touched including fruit and foliage.

Late blight is the least common blight on tomatoes, but it is, by far, the most destructive. Pale green, water soaked spots on the leaves quickly grow into purplish-black lesions and stems turn black. It attacks in rainy weather with cool nights and quickly infects fruits. Infected fruits show brown, crusty patches and rot quickly.

This is the blight that caused the Great Potato Famine of the 1840s and will quickly infect any potatoes planted nearby. All potatoes should be dug and disposed of as should all tomato plants and fruit affected by this tomato blight. Treatment is simple. Burn everything the fungus may have touched.

How to Prevent Tomato Blight

Once a blight on tomatoes takes hold, it’s very hard to control. After identification, tomato blight treatment begins with fungicide treatments, although when it comes to tomato blight, solutions really lie in prevention. Use fungicides before the fungus appears and they should be applied regularly throughout the season.

Fungus spores are spread by splashing water. Stay away from the garden while foliage is wet from dew or rain. Avoid watering in late afternoon or evening so that water can evaporate from the leaves and, if possible, water the ground and not the foliage. Most fungi grow best in the warm, wet dark.

Rotate crops as often as possible and never turn any tomato debris back into the soil. Use healthy transplants from a reliable nursery and remove damaged lower leaves regularly since that’s where most fungi attacks begin. Remove all plant debris at the end of the growing season so the spores have nowhere to over winter.

What is tomato blight? It’s a series of recurring fungal infections that can be curtailed with good garden housekeeping and simple fungicide treatments.

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