Blight Treatment – Symptoms And Control Of Southern Blight On Plants
By: Jackie Carroll
It happens to the best of us. Your garden grows so nice and then, without any warning, you turn around and notice all your healthy plants wilting and dying. Southern blight on plants is a common problem in many home gardens but it doesn’t have to be. How do you control southern blight before it takes out all of your plants? Keep reading to find out ways for controlling southern blight in gardens.
What is Southern Blight?
Southern blight, southern wilt, southern stem rot, and southern root rot all refer to the same disease. It is caused by the soil borne fungus Sclerotium rolfsii. The disease attacks a wide range of vegetable crops and ornamental plants at or below the soil line. Southern blight on plants is most likely to occur in the summer months when the soil is warm and moist.
Symptoms include discolored lower leaves, wilted foliage, and plant collapse and it usually results in the death of the plant. Upon close inspection, you may find an abundance of white hyphae or mycelia around the lower stem and roots and in the surrounding soil. When you find the hyphae or mycelia, the best course of action is to dispose of the plant and the soil surrounding it.
How Do You Control Southern Blight?
Controlling southern blight in the home garden is a challenge because the fungicides that are effective in treating the disease are only available to commercial growers. Home gardeners must depend on cultural practices to control the disease.
In the home garden, southern blight treatment begins with good sanitation to prevent the spread of the disease. The disease organism travels around the garden in bits of soil that clings to garden tools and the soles of shoes. Remove the soil before moving from one part of the garden to another. Quarantine new plants by growing them in a bed that is isolated from the rest of the garden until you are sure they are disease-free.
Remove and destroy diseased plants, along with the surrounding soil and any garden debris or mulch that has come in contact with them. Don’t transplant any nearby plants to other parts of the garden.
Soil solarization is an effective method of killing the fungus in the south, but in northern climates, the soil temperatures may not be high enough to eradicate the disease. Cover the soil with a clear plastic tarp and leave it in place while the heat builds up under it. The top two inches (5 cm.) of soil must come to a temperature of at least 122 degrees F. (50 C.) to kill the fungus.
If all else fails, consider calling in a landscape professional to treat your garden soil with the appropriate fungicides specified for southern blight treatment.
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Read more about Plant Diseases
Needle Blight Tree Disease - Identification and Control
Steve Nix is a member of the Society of American Foresters and a former forest resources analyst for the state of Alabama.
This group of blight diseases - including Diplodia, Dothistroma and brown spot - attacks conifers (mostly pines) by girdling needles and killing branch tips. These needle blights are caused by the fungus, Dothistroma pini mostly on western pines and Scirrhia acicola on longleaf and Scots pine needles.
Needle damage can cause major commercial and ornamental damage to conifers in North America significantly affecting the nursery and Christmas tree industries.
Infected needles often fall from the tree creating a symptomatic scorched, denuded look. The blight usually results in dramatic browning and dropping of the foliage beginning on the lower branches. It rarely attacks upper branches on conifers so the tree might not immediately die.
- Plastic garbage bags and ties
- White plastic mulch
- Natural mulch (e.g., straw or wood chips)
Check with your local university extension service, county agent or a trusted area nursery to determine if certain diseases, including blight diseases, are common in your area. Tomato seed and seedling packets usually contain information about which problems the tomatoes have been bred to resist.
Rotate tomatoes and related plants each year. Remember that tomatoes, potatoes, peppers and eggplants all belong to the nightshade family, so it's never a good idea to follow a pepper crop, for example, with potatoes or tomatoes. Plant any of these plants where a different family of plants, such as cereal crops or legumes.
How to Prevent Southern Blight on Your Tomato Plants
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.
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 day, digging in one part of the garden and then digging in a different part.
Not cleaning gardening tools between plantings is similar to a surgeon operating on a patient without cleaning their scalpel or hands. It is the quickest way to infect a an entire garden.
A commonly overlooked source of sclerotia is in the dirt that gets caught in the treads of garden shoes. Walking through an infected nursery or home improvement store and then tramping through the garden is all that is needed to bring southern blight home.
Simply knocking the mud out of the treads before entering the garden should be sufficient to knock off any sclerotia hiding in the mud.
Many gardeners prefer planting tomatoes in large patio containers. While this is easier than digging in tough earth, the heat and moisture that is created in containers is the exact environment that southern blight thrives in.
A gardener’s odds of avoiding the blight are greater when tomatoes are planted in the ground with wide spaces between plants to allow sufficient air circulation.
This circulation helps to ensure the stems remain dry at the soil line where the fungus is known to attack..
Some gardeners employ crop rotation to help decrease the number of sclerotia in the soil. The idea is that over time, when the sclerotia cannot find a suitable host, they begin to die off.
This is a plausible method that could feasibly take two or three years to succeed. Corn is one of the few plants that is fairly resistant to the blight.
Sclerotia seem to attach themselves to decaying plant matter on the ground before infecting healthy plants. Removing plant debris and keeping a tidy garden can help prevent the sclerotia from getting a foothold.
That said, composting plant debris is a common and effective gardening practice that does not have to be abandoned all together. Gardeners should simply bury the compost deep in the ground, at least 8 inches, as the sclerotia do not seem to be able to attach to plants unless they are in the top layers of soil.
Tilling the same ground in later years may bring the buried sclerotia back to the surface though, so careful attention should be payed when composing is used.
The best time to look for signs of southern blight is a day or two following a heavy rain after a long period of hot, dry weather. The humidity spurs the fungus into action and when left untreated can destroy an entire crop in a matter of days.
Tomatoes are not the only plants susceptible to infection. Such popular backyard garden plants as beans, peas, watermelon and carrots can be host plants for the fungus.
In fact, southern blight is so hardy it can live on over 500 different plants. Gardeners are well advised to do all they can to avoid the blight rather than attempt to treat it.
For more information about other similar tomato diseases, then these other guides might of use:
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Which Plants Are Vulnerable?
Many plants are vulnerable to bacterial blight, but plants with insect damage are much more likely to contract the disease than plants without an insect infestation. This is because as they feed on the plant foliage, insects create openings and access points for the bacterium to infect the plant.
Bacterial blight tends to affect woody plants like trees and shrubs. Other types of blight are more likely to affect edible garden plants like tomatoes and potatoes.