Tomato Gray Leaf Spot Control: Managing Gray Leaf Spot On Tomatoes

By: Bonnie L. Grant, Certified Urban Agriculturist

Sweet, juicy, ripe tomatoes from the garden are a treat worth waiting for until summer. Unfortunately, that lusted for crop can be brought down low by numerous diseases and pests. Gray leaf spot on tomatoes is a classic example and is one of the many diseases that can strike plants in the nightshade family. Tomato gray leaf spot control is actually quite simple provided you practice good cultivation and hygienic routines.

What is Tomato Gray Leaf Spot?

You head out to inspect your bountiful tomato plants only to discover brown to gray lesions with a yellow halo. This is a common fungal disease that affects plants at any stage of their life. This is a fungal disease and doesn’t affect those marvelous fruits, but it can diminish the health of the plant and, therefore, the quality of fruit production.

Gray leaf spot on tomatoes is caused by the fungus Stemphylium solani. It causes the lesions on leaves which become glazed in the center and crack. This produces shot holes as the disease progresses. Lesions grow up to 1/8 (.31cm.) across. The affected leaves die and drop. Stems may also develop spots, primarily young stems and petioles. The consistently dropped leaves can lead to sunscald on fruit, which can make the tomato unpalatable.

Tomatoes grown in the southern states are primarily affected. The disease favors moist, warm conditions, especially when moisture on leaves has no time to dry before evening dew arrives.

Causes of Gray Leaf Spot of Tomatoes

Treating gray leaf spot on tomatoes isn’t as important as making sure the plants never get the disease in the first place. Prevention is always easier, so it is necessary to understand where this disease hides.

In the garden, it will overwinter in plant debris. Not only tomatoes but other nightshade leaves and stems that have fallen can harbor the disease. In heavy spring rains and wind, the disease spreads through rain splash and wind.

Good hygienic measures go a long way to preventing the disease. Sanitation of tools and equipment can also prevent this fungus from moving into other unaffected beds.

Tomato Gray Leaf Spot Control

Some growers recommend treating gray leaf spot on tomatoes by using an early season fungicide. This can help prevent a variety of fungal diseases. There are also a few resistant tomato varieties if you can find them in your region.

The best tomato gray leaf spot control is crop rotation followed with seedbed sanitation and fungicide applications early in plant development. You can also hand pick off affected leaves to prevent the rapid spread of the fungus on the plant. Destroy any plant material rather than placing it in the compost pile.

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Tomato leaf spot diseases

There are three leaf spot diseases commonly found on garden tomatoes in Minnesota: Septoria leaf spot, early blight and bacterial spot.

At the earliest stages of disease, they are difficult to tell apart but the management practices listed below will work for all three disease problems.

Most tomato leaf spot diseases overwinter in the soil and then splash on to the lower leaves of the plant. As a result, the first leaf spots can be found on the lowest leaves closest to the ground.

Look for brown to black round spots that are the size of a pencil tip or larger.

  • The best control measure for tomato blight is prevention (see below).
  • Remove and destroy infected leaves (be sure to wash your hands afterwards).
  • Once blight is present and progresses, it becomes more resistant to biofungicide and fungicide. Treat it as soon as possible and on a schedule.
  • Organic fungicides. Treat organically with copper spray, which you can purchase online, at the hardware store, or home improvement center. Follow label directions. You can apply until the leaves are dripping, once a week and after each rain. Or you can treat it organically with a biofungicide like Serenade. Follow label instructions.
  • Chemical fungicides. Some gardeners prefer chemical fungicides, the best of which for tomatoes is chlorothalonil (sold as Fungonil, Daconil, or under other brand names. Check labels. You may also choose Mancozeb or Maneb, although these have longer wait times before you can harvest tomatoes safely than does chlorothalonil.

Other diseases (such as early blight, late blight, and gray leaf spot) can also be controlled by these biofungicides and fungicides, so application is multi-purpose.

Management Tips

  • Reduce thatch layer.
  • Irrigate deeply, but infrequently. This generally means one time per week with one inch of water. Always irrigate in the morning, which promotes quick drying of the foliage.
  • Avoid using post-emergent weed killers on the lawn while the disease is active.
  • Avoid medium to high nitrogen fertilizer levels.
  • Improve air circulation and light level on lawn. Limb up over-hanging trees and prune back nearby shrubs.
  • Mow at the proper height and only mow when the grass is dry. Bag and dispose of grass clippings if disease is present.
  • Control chinch bug infestations.
  • Use fungicide treatments as needed along with proper turfgrass culture. See Table 1.

Table 1. Fungicides to Control Gray Leaf Spot.

2 RTS = A ready-to-spray hose-end product.

If this document didn’t answer your questions, please contact HGIC at [email protected] or 1-888-656-9988.


Joey Williamson, PhD, HGIC Horticulture Extension Agent, Clemson University

This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.

Chemical Treatment

If gray mold is a known problem in your region, preventative applications of a fungicide may help. Clemson University's Cooperative Extension program recommends applying a product that contains chlorothalonil. Follow package directions before applying the spray. For example, a typical product calls for mixing 6 teaspoons of the fungicidal concentrate with one gallon of water, assuming a tomato patch that is about 200 square feet. Spray the plants thoroughly, focusing on the stems and leaves. You can repeat the applications about once a week, with a total of no more than seven applications.

  • Clemson Cooperative Extension: Gray Mold (Botrytis Blight)
  • University of California IPM Online: Tomato -- Gray Mold
  • Rodale's Ultimate Encyclopedia of Organic Gardening: Fern Marshall Bradley, et al

Ellen Douglas has written on food, gardening, education and the arts since 1992. Douglas has worked as a staff reporter for the Lakeville Journal newspaper group. Previously, she served as a communication specialist in the nonprofit field. She received her Bachelor of Arts from the University of Connecticut.

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