Tomato Blight: What It Is And How To Save Your Plants

If you've started to notice dark spots, brown leaves, or yellow tissue on your tomato plants, you might be dealing with a type of blight. These diseases primarily affect nightshade vegetables of the Solanaceae family, such as tomatoes, potatoes, eggplants, and peppers. While blight can affect various plants, there are three main types that can destroy tomato plants: early blight, late blight, and Septoria leaf spot. If left untreated, these diseases can take out entire fields of produce and ruin tomato production.

Early blight is a plant disease caused by two types of fungus called Alternaria solani and Alternaria tomatophila; the latter is typically the cause of early blight on tomato plants. Although the name might make you believe otherwise, early blight can occur at any point during the growing season. Late blight, spawned by Phytophthora infestans, which is a water mold, is a destructive disease capable of spreading quickly if left untreated. Septoria leaf spot, which is caused by the fungus Septoria lycopersici, typically harms tomatoes but can affect other types of plants as well. Each blight type has different symptoms and varying degrees of severity, but each one needs to be treated immediately to save your tomatoes.

From a distance, early blight, late blight, and Septoria leaf spot may look similar, but each type of blight targets specific areas of your tomato plants. It's important to recognize which variety you are dealing with before beginning treatment. Early blight typically starts on the bottom of the plant, with round dark spots and rings forming on older leaves. If untreated, early blight may start to turn the plant yellow, sometimes forming spots on the tomatoes themselves. Late blight, which was the root of the Great Famine in 1800s Ireland, spreads quickly in moist environments and leaves behind shapeless dark blotches on tomato plants. Often these spots are enclosed in lighter-colored edges. Lastly, Septoria leaf spot starts as small, dark, and wet spots, which usually appear on the lower leaves after the plant has begun producing tomatoes. They eventually turn white with dark spots.

Each of these three blight types can cause a decline in the health of your tomato plants, and any fruit affected by these diseases should not be eaten. While it may be discouraging to see these symptoms, there is no need to panic. There are several ways to treat your plants, from removing affected parts to turning to fungicide, depending on how severe the infection is in your garden.

Once you've determined what type of blight your tomatoes are experiencing, you can treat them accordingly. While early blight cannot be cured, you can stop the spread if you catch the disease early enough. Add mulch and compost to your garden to boost the health of your plants. Watering from below or using a drip irrigation system can also help prevent the spread of blight, as soil splash and a damp environment can worsen blight. If you've determined your tomatoes are suffering from early blight, late blight, or Septoria leaf spot, you should remove affected fruits and leaves. Do not compost these, but burn or toss them.

To keep your tomato plants blight-free in the future, you can try a few different tactics. When you purchase tomato plants, make sure to stay vigilant in checking the health of the seedlings to ensure you're not bringing blight into your garden. You can also opt to plant tomato varieties that are more resistant to blight, such as 'Juliet' or 'Plum Regal' tomatoes. When planting your seedlings, ensure they are spaced well apart to reduce the risk of humidity, and keep them free of weeds. If your garden's case of blight is severe, you can opt for the use of fungicides, such as mancozeb or copper fungicides.