Tomato Southern Blight Treatments

early tomato blight

As temperatures climb, tomato plants thrive with regular watering and fertilization, often producing masses of fruit. However, when warm rains follow hot, dry spells, a fungus lying in the soil called sclerotium rolfsii, or southern blight, can gain a foothold in any garden and destroy an entire tomato bed overnight.

Causes and Symptoms

Southern blight is a hearty strain of fungus that is capable of living dormant in soil for three to four years. It is easily transferred through unsterilized soil, on garden tools and pots and can even contaminate a home garden when tracked from an infected nursery in the treads of shoes.

It is easy to spot tomato plants that have been infected with southern blight. A day or two after a rainstorm their leaves turn yellow and the plant begins to quickly wilt. An inspection of the tomato stems at the soil line will reveal a white fungus and small, round growths that resemble white or brown mustard seeds. Infected plants will likely collapse at this infection point and simply fall over dead in a matter of days.

Treatments and Control

Home gardeners and commercial growers alike agree that preventing southern blight is highly recommended over attempting to treat it. Once established, treatments to kill it are time consuming, expensive, and effective results are inconsistent. Follow these simple rules of prevention to minimize the risk of southern blight:

  • Buy plants from reputable growers that sterilize reused pots and gardening tools

  • Thoroughly clean all home gardening equipment after use

  • Do not allow dead leaves, blooms and garden produce to decompose on the soil

Once southern blight has become established in the ground, treating the soil and not the plants is the most effective way to attempt to eradicate the problem. The part of the fungus resembling mustard seeds is called sclerotia, which multiply in the soil when allowed to remain on infected plants.

Removing all infected plants and using corn for crop rotation, one of the very few plants that is naturally resistant to the fungus, helps to prevent it from multiplying.

Sclerotia prefer a hot, moist environment often found in the soil of well-drained pots. While patio tomatoes can be easier to plant and maintain than digging in the ground, pots provide conditions that are most conducive to fungal growth.

Wide spacing of tomato plants in the ground allows healthy air circulation and provides a distance barrier against the spreading of the fungus. This allows for easy clean up of plant debris between the plants that the sclerotia use to first establish themselves.

Southern blight is an invasive fungus that is easy to detect but extremely difficult to eliminate. As always, prevention is the best medicine. That, followed by close inspections of the tomato stem after a rainfall and fast action to remove all infected plants and soil immediately will help to lessen the impact of southern blight.

Comments from Other Gardeners
  • rick padgett says:

    I have something this year that I can not get rid of.First signs of disease, edge of leaves turn brown.Just outer edge.Will continue to cover leaf and will turn black, gray.Leaf will die and disease spread to other leaves very rapidly.
    First saw edge browing 4 weeks after planting.Started with Daconil and removed damaged leaves.Came back with compost tea foliar spray.Waited a week and saw return, hit with copper, removed diseased leaves.Waited 6/8 days saw again and went clorox 5% spray.Killed all diseased plants.Removed and came back with compost tea.
    No leaves no tomatoes.Have NEVER seen anything like this.No Summer tomato crop.Sent sample to Clemson Plant Pathology Lab, no positive ID.

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