Early Tomato Blight: How to Identify, Prevent, and Treat
When left untreated, this fungal disease can cause your crops to rot
The Spruce / Adrienne Legault
Reviewed by Kathleen Miller
Early blight can affect almost all parts of a tomato plant, including the leaves, stems, and fruits. The plants may not die, but they will be weakened and will set fewer tomatoes than normal. Early blight generally attacks older plants, but it can also occur on seedlings. Stressed plants or plants in poor health are especially susceptible. Early blight is also a problem with potatoes.
Early blight is a difficult enough disease to deal with, but don't confuse it with the much more problematic late blight that can quickly kill tomato plants and spread for miles.
What Is Tomato Blight?
Tomato blight is a disease caused by a fungus, depending on which type of blight is affecting the vegetable. However, more than one type of blight can attack tomatoes at the same time. There are three types of tomato blight caused by different fungi that all present somewhat similarly.
Types of Tomato Blight
Early Blight: Early blight is a common tomato disease caused by the fungus Alternaria solani. It appears as large, irregular spots with yellow halos on leaves that eventually yellow.
Late Blight: Late blight is a water mold caused by the fungus Phytophthora infestans. Leaves have large, dark brown blotches with grayish edges that turn to large sections of dry brown foliage.
Septoria Leaf Spot: Septoria leaf spot is caused by the fungus Septoria lycopersici. An abundance of spots appear small and round with light centers.
Symptoms of Early Blight on Tomatoes
Early blight is sometimes confused with Septoria leaf spot. They both form spots on the leaves, which eventually turn yellow and die off, but Septoria also forms fruiting bodies that look like tiny filaments coming from the spots.
On Older Plants: Dark spots with concentric rings develop on older leaves first. The surrounding leaf area may turn yellow. Affected leaves may die prematurely, exposing the fruits to sun-scald.
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. Plants may survive, but they will not thrive or produce many tomatoes.
On Tomato 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.
On 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.
What Causes 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 over-winter 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.
Early Blight Control and Prevention
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
Air Circulation: Provide plenty of space for the plants. Good airflow will help keep the plants dry.
Stakes for Plants: Staking or caging tomato plants ensures that the foliage does not touch the ground and stays away from spores.
Fungicides: 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
Certified Seed: Buy seeds and seedlings from reputable sources and inspect all plants before putting them in your garden.
Garden Sanitation: Since early blight can overwinter on plant debris and in the soil, sanitation is essential. So many tomato diseases can come into your garden this way so it's very important to clean up all plant residue at the end of the season.
Rotate Crops: If you have an outbreak of early blight, find somewhere else to plant your tomatoes next year, even if it's in containers.
Separate Plants of the Same Family: 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 is completely immune.
Aunt Ginny's Purple: Heirloom, indeterminate, beefsteak (16 oz.)
Big Rainbow: Heirloom, indeterminate, bi-color beefsteak (16 oz.)
Black Plum: Heirloom, indeterminate, plum (2 in.)
Juliet: Hybrid, indeterminate, cherry (1 ounce)
Legend: Open-pollinated, determinate, beefsteak (14-16 ounces)
Manyel: Heirloom, indeterminate, yellow globe (8-10 ounces)
Matt’s Wild Cherry: Heirloom, indeterminate, cherry (1/2 inch)
Mountain Supreme: Hybrid, determinate, globe (6-8 oz.)
Mountain Fresh Plus: Hybrid, determinate, globe (12 ounces)
Old Brooks: Heirloom, indeterminate, globe (6-8 ounces)
Tigerella (aka Mr. Stripey): Heirloom, indeterminate, globe (4-6 oz.)
Tommy Toe: Heirloom, indeterminate, cherry (1 inch)
Frequently Asked Questions
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.
