Septoria Leaf Spot

Septoria leaf spot (also called Septoria blight) is a very common foliar tomato disease that also infects eggplant and pepper plants. It and early blight comprise the two most common foliar tomato diseases.

Septoria Leaf Spot
Septoria Leaf Spot

Caused by the fungus Septoria lycopersici, it can be very destructive. The disease begins when fungal spores are spread from other plants, workers, equipment, contaminated seed, or insects. Plants are most open for infection when temperatures are moderate and moisture is abundant.

How to Identify Septoria Leaf Spot

Septoria Leaf Spot
Paul Bachi, University of Kentucky
Research & Education Center,
Bugwood.org
Septoria Leaf Spot
Division of Plant Industry Archive,
Florida Department of Agriculture and Consumer Services,
Bugwood.org
  • Leaf spot symptoms are first seen on lower leaves especially after the first fruit sets.
  • Spots may also appear on stems but rarely on fruit.
  • Spots may appear as tan with a darker brown border
  • A small yellow border is visible around each spot.
  • Spots can merge until the leaf  shrivels.
  • Severe cases can cause the leaves to turn yellow, brown, then wither.

Causes

  • The disease is worsened by moderate temperatures (20˚C to 25˚C/68˚F to 77˚F) and abundant rainfall.
  • Easily spread by splashing water.
  • The fungus survives between seasons on infected plant debris.
  • Extended periods of leaf wetness, high humidity, and warm temperatures exacerbate the development and spread of the disease.

Preventative Measures

  • Sterilize the soil and avoid use of wooden stakes, as the fungus can survive between seasons, or disinfect or use new stakes each season.
  • Plant only disease-free seeds and transplants.
  • Prune lowest branches to prevent soil contact.
  • Avoid over-watering and overhead irrigation. Promote leaf drying by watering early in the day.
  • Rotate crops each year.
  • Two to four inches of mulch (such as dry grass clippings) placed on the soil around the plants will inhibit release of fungal spores.

Treatments

Natural remedies

  • No biological control strategies have been discovered yet.

Chemical treatments

  • Fungicides are very effective in control of septoria leaf spot; copper, chlorothalonil, and mancozeb fungicides are available for homeowner use. (See below for suitable products available through Amazon.com.)
  • Use fungicide in combination with as many preventative methods as possible to be most effective.

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Credits for technical content

  1. High Plains IPM Guide, a cooperative effort of the University of Wyoming, University of Nebraska, Colorado State University and Montana State University.



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