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Steps to prevent and manage tomato leaf spot diseases

Irregular lesions with a yellow halo and target pattern are

Irregular lesions with a yellow halo and target pattern are classic early blight symptoms

We wait what seems like a long time before the first garden tomatoes start to ripen. This is especially true if you grew them indoors first from seed to transplant stage. Invariably, our tomato plants will face seasonal challenges, such as excessive heat and drought, stink bugs, stakes and supports that fail to hold up. The one problem we can always count on are the twin torments of all tomato gardeners – Septoria leaf spot and early blight.

Septoria leaf spot appears as small distinct lesions with dark borders and tan centers

These two fungal leaf spot diseases begin their devastation by infecting lower leaves. The disease moves up the plant, spreading rapidly during hot, humid, wet weather. The two diseases often co-occur and are managed the same way:


  1. Provide adequate spacing to increase air circulation and remove all suckers that emerge from the plant base
  2. Monitor transplants carefully for signs of this disease.
  3. Keep plants well mulched to minimize soil splashing.
  4. Water plants at their base. Avoid wetting the foliage.
  5. Prune off the lowest 3-4 leaf branches once plants are well-established and starting to develop fruits. This increases air circulation and slows down infections.
  6. Remove infected leaves during the growing season and remove all infected plant parts at the end of the season.
  7. Apply a synthetic fungicide or an organic fungicide (fixed copper) according to label directions, early in the season, when symptoms appear to slow the spread of the disease. This may be helpful where the disease causes severe blighting each year leading to reduced yields.
  8. Diseased plant parts can be shredded and composted if “hot composting” techniques reused (pile temperatures should exceed 120° F throughout and piles should be turned two to three times).

Before pruning: Typical tomato leaves grow at ground level where fungal spores from the two diseases can begin an infection.

After pruning: Lower branches removed with pruners to improve air circulation around leaves and stems.

Article By: Jon Traunfeld
Home and Garden Information Center Director

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