How to Prevent Southern Blight on Your Tomato Plants | GP

Southern blight is dreaded by home gardeners and commercial growers alike. The fungus that causes the blight is believed to be able to lie dormant in the soil for up to four years.

Once temperature and humidity conditions are right and and it finds a host plant on which to become established, it is extremely difficult to eradicate.

The southern blight fungus Sclerotium rolfsii, is hard to miss in healthy, green tomato plants. The leaves of the plants turn a sickly yellow color and begin wilting very quickly.

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A lesion forms around the collar of the tomato stem, usually covered in a white mold. Within the patch of mold, round beads of a white or brown color resembling mustard seeds can be seen lying in the soil.

These beads, called sclerotia are the source of the fungus. Prevention is far preferred over trying to remove the blight once it has become established.

There are a number of measures a conscientious gardener can take to help ensure the health of a garden.

Seedlings purchased from any nursery that reuses potting soil or does not sterilize reused containers are often the overlooked source of an initial infestation.

The sclerotia are small enough that many gardeners do not even notice them mixed into the soil of the seedlings. When temperatures soar and humidity rises, the seedling will quickly die and the healthy sclerotia multiply in the soil.

Sclerotia are often confined to one area of soil in a garden if there is no host plant available for them to live on. Most gardeners plant multiple plants in different parts of the garden on the same