Septoria Leaf Spot

• Numerous small, circular spots on lower leaves — pale tan or gray centers with dark brown borders
• Small black dots (pycnidia — spore-producing structures) visible in the center of spots with a hand lens
• Spots are smaller and more numerous than early blight lesions — no bull's-eye pattern
• Leaves yellow and drop, starting at the bottom and progressing upward
• Disease often appears after the first wet period when plants begin to fruit

Septoria lycopersici overwinters in infected plant debris in the soil. Spores are splash-dispersed during rain and irrigation. Warm, wet weather and heavy dew favor rapid spread. The disease is common wherever tomatoes are grown in humid climates. It rarely kills plants outright but can significantly reduce yield by defoliating the lower canopy and exposing fruit to sunscald.

1. 01Mulch at planting to reduce soil splash onto lower foliage
2. 02Water at the base of plants and avoid wetting foliage
3. 03Remove infected lower leaves as soon as spots appear — dispose of, do not compost
4. 04Apply copper-based fungicide or chlorothalonil preventively when wet weather is forecast and disease pressure is building
5. 05Stake or cage plants to keep foliage off the ground and improve airflow
6. 06Rotate tomatoes out of the same bed for at least two seasons

Septoria can look similar to bacterial speck or early blight to the untrained eye. If you're applying fungicides and not seeing improvement, an extension plant diagnostic lab can confirm the pathogen and rule out bacterial causes that respond differently to treatment.

• Septoria Leaf Spot of Tomato— University of Minnesota Extension
• Septoria Leaf Spot— Ohio State University Extension