Early Blight: A Common Tomato Disease
What is Early Blight?
Early blight is a fungal disease that affects tomatoes, causing spots on the leaves, stems, and fruits. It is caused by the fungus Alternaria solani. Early blight is a common problem for tomato growers, especially in warm, humid climates.
Symptoms of Early Blight
Early blight can affect all parts of the tomato plant, including the leaves, stems, and fruits.
- Leaves: Early blight typically appears on older leaves first. Dark spots with concentric rings develop on the leaves, which eventually turn yellow and die off.
- Stems: Dark lesions on the stems start off small and are slightly sunken. As they get larger, they elongate and you will start to see concentric markings like the spots on the leaves. Spots that form near ground level can cause some girdling of the stem or collar rot.
- Fruits: If early blight gets on the fruits, spots will begin at the stem end, forming a dark, leathery, sunken area with concentric rings. Both green and ripe tomatoes can be affected.
- Seedlings: Affected seedlings will have dark spots on their leaves and stems. They may even develop the disease on their cotyledon leaves. Stems often wind up girdled.
Causes of Early Blight
The early blight fungus can come from many sources. It can be in the soil, or it can already be on seeds or seedlings you purchase. It can even overwinter in the diseased debris of your tomato plants and it can persist in the soil or debris for at least one year. Although early blight can occur in any type of weather, it favors damp conditions, like frequent rain or even heavy dews.
Control and Prevention of Early Blight
Some tomato varieties offer a bit of resistance to early blight, although none are fully immune to it. Even if you buy a resistant variety, early blight is a very common problem with tomato plants and you may not be able to avoid it completely. These measures, however, can help you keep it under control and prevent the issue.
Control
- Provide plenty of space for the plants. Good airflow will help keep the plants dry.
- Stake or cage tomato plants to ensure that the foliage does not touch the ground and stays away from spores.
- Keep tabs on your plants, especially during wet weather or if your plants become stressed. If you see signs of blight on a single plant, removing the plant is your best option. Fungicides containing the active ingredients Penthiopyrad or Boscalid will be the most effective.
Prevention
- Buy seeds and seedlings from reputable sources and inspect all plants before putting them in your garden.
- Since early blight can overwinter on plant debris and in the soil, sanitation is essential. Clean up all plant residue at the end of the season.
- If you have an outbreak of early blight, find somewhere else to plant your tomatoes next year, even if it’s in containers.
- Do not grow nightshade (Solanum) plants, such as eggplant, potatoes, and peppers alongside tomatoes to avoid passing along the same infections to each other. Instead, be aware of the correct companion plantings with tomatoes to avoid blight.
Tomato Varieties with Some Resistance to Early Blight
All of these varieties are somewhat resistant to early blight, but none are completely immune.
- Aunt Ginny’s Purple
- Big Rainbow
- Black Plum
- Juliet
- Legend
- Manyel
- Matt’s Wild Cherry
- Mountain Supreme
- Mountain Fresh Plus
- Old Brooks
- Tigerella (aka Mr. Stripey)
- Tommy Toe
FAQs
Does tomato blight stay in the soil?
Early blight and septoria leaf spot spores can survive in the ground, even over the winter, but late blight cannot survive winters. Early blight and septoria can return year after year in the soil if not treated or handled through preventative methods, such as crop rotation.
Can you still eat tomatoes with blight?
Blight can’t affect humans, but the fungus can cause other issues in the vegetable and the flavor may be off. If you see an unblemished tomato but affected leaves, try to grab the vegetable to eat or can before it is further diseased.
Does tomato blight spread to other plants?
Yes, tomato blight can be spread to other plants such as potatoes and nightshade vegetables.
How do you sterilize soil after tomato blight?
Fungicides can kill blight spores, but solarizing the soil is another way to sterilize soilborne pathogens that cause blight. Soil solarization is a method that uses a clear plastic covering to bring the soil to high temperatures through captured radiant energy from the sun to kill pathogens.