What is Septoria Leaf Spot?

Septoria leaf spot is a fungal disease that affects a wide range of plants. It usually begins as small, water-soaked spots on the lower leaves of the plant and progresses into larger, circular lesions with a gray or tan center and dark border. The disease can cause significant defoliation, reducing plant vigor and yield.

Host plants include:

Nightshade family members: Tomatoes, Potatoes, Eggplants, Peppers, and Petunias.

Herbaceous plants: Artemisia, Baptisia, Campanula, Chrysanthemum, Coreopsis, Delphinium, Dianthus, Echinacea, Gaillardia, Heuchera, Lamium, Lathyrus, Lupinus, Lychnis, Monarda, Potentilla, Ratibida, Rudbeckia, Stachys, Veronica, and Viola.

What causes Septoria Leaf Spot?

Septoria leaf spot is caused by a fungus called Septoria lycopersici. The fungus thrives in warm and humid weather and can spread through the air, water, or infected plant debris. It attacks weakened plants, particularly those stressed by poor growing conditions, lack of nutrients, or poor drainage.

The fungus survives the winter in infected plant debris and soil. The spores produced by the fungus are spread by wind, rain, and splashing water. The spores infect the lower leaves of the plant, and then the disease spreads upward. The symptoms of the disease become apparent as the weather warms in the summer. The fungus can survive in the soil for several years and infect plants in the same location year after year.

What are the Symptoms?

• Small, water-soaked spots on the lower leaves of the plant eventually turn brown and develop a tan or gray center.
• The center of the spot may have tiny black specks (fungal fruiting bodies).
• The spots can merge together to form larger lesions that kill off the leaves.
• The disease usually begins on the lower leaves and moves up the plant as the season progresses.
• Severely infected plants may defoliate early, which can reduce yield in fruiting plants.

How to Control and Prevent Septoria Leaf Spot?

To control and prevent Septoria leaf spot, here are some steps you can take:

1. Plants: Maintain good plant hygiene by removing and destroying infected plant material.

2. Clean up: Clean up plant debris in the fall.

3. Disease-resistant plants: Use disease-free seeds and disease-resistant cultivars.

4. Water: Water plants in the morning, avoiding wetting the leaves, as this can promote fungal growth.

5. Mulch: Use mulch to prevent the splashing of spores from the soil onto the leaves.

6. Products: Consider using copper-based fungicides, neem oil, or sulfur sprays to prevent and control the Septoria leaf spot. Follow the instructions on the product label.

7. Crop rotation: Rotate crops and avoid planting the same susceptible plants in the same spot each year.

8. Prune: Prune the lower leaves to increase air circulation, which can help reduce the humidity that promotes fungal growth.

9. Removal: Finally, if the infection is severe, you may need to remove and destroy the entire plant to prevent the disease from spreading to other plants.