Early Blight in Tomatoes – Identification and Treatment

Blight is a fungal disease that commonly affects tomato plants. It thrives in damp and warm conditions. Blight systematically destroys the plant by killing the leaves, stems, and fruit tissues. Blight in tomatoes can be controlled when identifies earlier to save the plant.

Dark spots on the tomato leaves, stems and fruits are the telltale signs that your plants may be suffering from blight. It easily spreads from one plant to the other causing the leaves to discolor, rot and fall off prematurely.

The severity of the disease depends on the type. There are three types of tomato blight namely early blight, late blight, and septoria leaf spot. Early blight will only attack older plants while late blight can affect plants at any growth stage.

Tomato blight identification

When looking out for signs of blight in tomatoes, be keen to identify the disease positively as symptoms may be similar to other problems. So, which type of blight may be affecting your plants?

Early Blight

Early blight is a common fungal infection in tomatoes. It is caused by the fungus Alternaria solani. It normally appears after a heavy fruit set. It can affect almost all parts of the plant that include the leaves, stems, and fruits.

This infection causes dark spots with concentric rings to appear on the older leaves of the plant. The surrounding plant tissues may turn yellow, then brown before dying and falling off prematurely. It also causes cankers or sunken dark lesions to appear on the stems.

Early blight may not affect the fruits directly but the loss of protective leaves or foliage may leave the frits exposed to the harmful effects of the sun like the sunscalds. Early blight is considered to be dangerous when not controlled, the plant may survive but will not thrive. The production is also negatively affected.

Late Blight

Late blight is also a fungal infection. It is caused by phytophthora infestants fungus. It can affect tomatoes at any growth stage. It is the least common tomato blight but the most dangerous. Late blight is characterized by pale green water-soaked spots on the leaves that eventually turn into purplish—black lesions.

The symptoms normally start to appear on the edges of leaves before spreading in the whole leave and towards the stem. You may also notice the formation of white mildew on the undersurface of the affected leaves. The stems also change into a dark color.

Late blight is common in humid conditions and can spread to the fruits if not controlled. It can be the reason why tomatoes rot on the vine. Treatment ranges from using organic or chemical fungicides to uprooting and destroying the affected plants which can help to control the spread of this infection in your garden.

Septoria Leaf Spot

Septoria leaf spot is the most common but least destructive type of blight. It is also a fungal infection caused by septoria lycopersici fungus. Just like early blight, the symptoms of septoria leaf spots normally start to appear at the base of the plant on the older leaves.

This infection is characterized by tiny but many brown spots that appear on the lower older leaves. The spots continue to increase in size before the leaf dies and falls off prematurely. However, the septoria leaf spot only affects the leaves and not the fruits.

What Causes Tomato Blight?

Tomato blight belongs to a category of diseases caused by fungus-like microorganisms that spread through tomato foliage. Fungus thrives well especially in wet and warm weather conditions. Tomato blight causes the leaves to discolor, die and fall off prematurely.

There are three known types of tomato blight, early blight caused by Alternaria solani, late blight as a result of phytophthora infestans, and lastly the septoria leaf spot due to septoria lycopersici. Although treatment of the three types of blight is the same, the symptoms are different from one another.

Early blight normally attacks tomato plants after the onset of first fruits while the late blight can affect the plant at any growth stage. Other factors like Poor tomato plant management, watering the foliage, overcrowding, and using infected garden tools can provide ample conditions for the growth of the fungus.

How do I know if my tomatoes have blight?

Observing your tomato plants keenly and closely can help you to identify the earliest symptoms of blight. Blight can affect your plants at any growth stage. Blight can be managed easily when the symptoms are discovered early. Be sure to observe for:

Symptoms on seedlings

Given that blight can affect tomato plants at any growth stage, be sure to start observing your plants early enough for symptoms. The affected seedling will have small dark spots on their leave and even the stems. The stems may also wind up girdled.

Symptoms on older plants

Early blight normally attacks older tomato plants, especially after setting the first fruits. The affected plants will start to develop dark spots with concentric rings on the older leaves. The affected leaves dry up and fall off from the plant prematurely. 

Early blight also affects the fruits indirectly. After causing the affected plants to shed off the leaves, the fruits are left exposed to harsh environmental conditions that may result in sunscald.

Blight also causes slightly sunken dark lesions to appear on the stems, they become large over some time and you may start to observe concentric markings that resemble the spots on the leaves. The spots at the base of the stem may also cause some girdling.

Symptoms on the fruits

Blight causes a tomato plant to lose its leaves prematurely. The fruits become exposed to the sun and can develop sunscalds. Leaves also play a very important role in the process of photosynthesis. This means that the affected tomato plants will not be able to produce enough energy to sustain themselves and the fruits.

This can result in flowers falling off the vine prematurely or fruiting into a few tomatoes that are too small.

Tomato Early Blight Treatment

Once you identify early symptoms of blight, the next immediate action should be treatment. Allowing early blight to progress without treatment can damage all of your plants. It may also become resistant to bio fungicides and other fungicides. This tomato infection can be treated through:

1. Organic Fungicides

If you are practicing organic gardening, blight can be controlled organically using copper spray. It can be obtained from organic drug stores in your locality or can be purchased online. Spray it directly on the affected leave or the whole plant once a week or after rain. However, you are supposed to read the manufacturer’s instructions well before using.

2. Chemical Fungicides

Approved chemical fungicides also give the best result in the treatment of early blight. It can be obtained from a drug store within your locality. Chemical fungicides like chlorothalonil are effective for early blight treatment. It is found under various brand names like Fungoid or Deconil among others.

How to prevent early blight in tomatoes

Early blight and other types like late blight and septoria leaf spots can be treated using organic or chemical fungicides. However, it is said that prevention is better than treatment. There are various measures you can put in place to ensure your tomatoes are not infected with blight. Some of them include:

• Practicing crop rotation. Early blight spores can remain dormant in the soil for some period of time. It is likely to affect your tomatoes if you are planting the nightshade family crops in the same place in your garden year in and year out.
• Applying much around your tomato plants. Apart from preserving soil moisture, mulching can also save your tomatoes from diseases like blight. It prevents direct contact of leaves and fruits with the soil that may be harboring early blight spores.
• Planting tomatoes at a correct spacing. Tomato plants should be at least 24 inches from one another to promote free air circulation. Crowded plants provide moist and warm conditions that promote the growth of fungal infections.
• Staking tomato plants early. To prevent tomato leaves from coming into contact with the soil, stake your plants early.
• Uprooting and destroying the affected plants. To prevent the fungus from spreading to other healthy plants, remove and destroy the affected ones.
• Planting tomato varieties that are resistant to early blight. Go for tomato varieties that are somehow resistant to early blight like a big rainbow, Juliet, Legend, and Manyel among others. Although they are not completely immune to early blight.
• Watering at the base of the plant. Use drip irrigation that delivers water to the soil at the base of the plant. Overhead watering encourages the growth of fungus.
• Planting tomatoes in raised beds. To improve drainage around your plants, be sure to plant them in raised beds.

Final Thoughts

Inspect your tomato plants in the garden occasionally for any signs of damage or dark spots. Blight is easily managed when the symptoms are noticed early. Using organic or bio fungicides can help to save your tomato plants. Uprooting and burning the affected plants can also help to prevent the spread of blight to other healthy plants.

References

Tomato Diseases and Disorders in the Home Garden – The Pennsylvania State University

Growing Tomatoes in the Home Garden – Ohio State University Extension

Diagnosing and Controlling Fungal Diseases of Tomato in the Home Garden by Andy Wyenandt, Extension Specialist in Vegetable Pathology Peter Nitzsche, Agriculture and Natural Resources Agent, Morris County.