How to Handle Tomato Blight

Tomato blight is a fungal infection that thrives in moist environments.

Tomato blight refers to two distinct diseases that affect tomato plants. Alternaria solani is the fungus that causes early blight in tomatoes, and Phytophthora infestans causes late blight. Both are fungal infections, so the treatments and prevention methods are the same. Late blight affects the entire plant, including the stems and fruit, but early blight favors just the leaves. The symptoms of blight include dark lesions on the plant that turn into brown spots that grow until the entire leaf, stem or fruit dies and rots. A white fuzzy growth also develops that is comprised of the reproductive spores of the fungi.

Things You'll Need

• Garbage bag
• Fungicide
• Irrigation system or garden hose
• Pruning shears

Instructions

1. Remove any diseased plants by hand and destroy them. Place the plants in a garbage bag and close the bag. Leave the bag in the sun a few days to kill the spores before placing the bag in the trash. Removing diseased plants immediately helps prevent the spread of the disease to nearby gardens and farms.

2. Spray a fungicide, like chlorothalonil, copper, potassium bicarbonate or hydrogen dioxide on healthy plants regularly. Follow the manufacture's directions and spray the plants every seven to 14 days on a regular schedule to prevent infections. A fungicide will not save plants that are already infected.

3. Irrigate in the mornings at the soil level so the afternoon sun can effectively dry the plants. Fungi need moist environments to grow and thrive. Watering from above in the evenings creates a damp environment on the foliage, which promotes fungal growth.

4. Prune crowded or overgrown plants to increase air flow between the plantings. Proper plant spacing is essential, but the spacing required depends on the tomato variety. If the plants have grown together, separate them with pruning shears and thin the plants with a selective removal of stems. Crowded plantings reduce air flow, which increases moisture on the foliage and promotes fungal growth.

Tips & Warnings

• Follow proper tomato plant care including watering and fertilizing. Healthy plants naturally resist infections better than stressed plants that lack essential nutrients.

References

• University of Maine: Early Blight of Tomato
• Ohio State University Extension; Late Blight of Potato and Tomato; Randal Rowe, et al.
• University of Maryland College of Agriculture & Natural Resources; Late Blight; Jon Traunfeld