Septoria Leaf Spot

Need to know: 

• Optimal conditions are wet environments. 
• Symptoms include small dark spots on lower leaves which begin to grow. 
• Septoria leaf spot overwinters on infected debris from previous years. 
• Cultural techniques can be used to reduce risk of disease. 
• Fungicide sprays are likely to be needed if disease is present. 

Overview of septoria leaf spot 

Wet conditions favor the development of fungal blights of tomato.  Septoria leaf spot and blight is a common foliage disease of tomato caused by Septoria lycopersici.

Symptoms of septoria leaf spot

Symptoms are evident in the foliage, particularly older (lower) leaves. Septoria blight causes numerous small (about 1/8" to 1/4" in diameter) brown spots that develop light tan to white center as they age. Rapid defoliation occurs soon after if left untreated.The overall effect of both blights is similar. Leaves turn yellow, brown, then wither and die. 

Signs of septoria leaf spot

Small black fruiting structures (pycnidia) can be seen in the center of the lesions after they have grown in size. 

Disease cycle of septoria leaf spot

Septoria blight and early blight both overwinter on infected debris from previous years. If there are only a few plants in a garden, the progress of the blights may be slowed somewhat by removing infected leaves as they appear.

Type of Sample Needed for Diagnosis and Confirmation

The Iowa State University Plant & Insect Diagnostic Clinic can help you to investigate and confirm if you plant has this disease. Please see our website for current forms, fees, and instructions on collecting and packing samples. Contact information for each states diagnostic laboratory for U.S. residents.  If your sample is from outside of Iowa please do not submit it to the Plant & Insect Diagnostic Clinic without contacting us

Management of septoria leaf spot

Nevertheless, fungicide sprays are likely to be needed if these diseases are present. Many products are labeled, however seldom infective if used alone without other management tactics. Cultural techniques can help to reduce the risk of foliar blight outbreaks, but it takes some advanced planning. At the end of the season, remove as much tomato plant debris as possible from the planting. Till thoroughly in the fall in order to break up remaining infected debris. Rotation away from tomatoes and potatoes for 3 to 4 years also helps to break the debris link in the disease cycle. If a long rotation is not feasible, a 2-4" layer of organic mulch (chopped deciduous tree leaves, grass clippings, straw, etc.) placed over the soil surface after transplanting acts as a barrier against release of fungal spores. Planting density or spacing, as well as sucker pruning and trellising improve air movement and reduce humidity needed for disease development.  Reducing overhead watering (to reduce spores splashing from leaf to leaf and from leaf debris) also helps.

Further Information about septoria leaf spot

For more information on Septoria leaf spot and other common tomato diseases that you can download for free at Tomato Diseases and Disorders

Improve sanitation in the garden can contribute to reducing the amount of the pathogen present for next year.

Fungicide applications may be avoided by following good Integrated Pest Management practices like those listed in this encyclopedia article. Often, the only preventative application is effective to manage plant diseases. If the problem requires a fungicide, state law requires the user to read and follow all labels accordingly. For more information, read Proper fungicide use.