Southern blight on tomatoes

There are many different diseases and conditions that can harm your tomato plant and some of them are very invasive. Diseases that harm a tomato plant can end up killing the plant all together or it could invade the soil infecting other crops. A tomato plant is very fragile and you need to take care of it to ensure that a devastating disease does not occur. If you have a tomato plant then you need to check out the various diseases that can occur and learn how to prevent them from happening. One of the most devastating and intrusive tomato diseases you can get is the southern blight. Southern blight can wreck your tomato plant and make replanting impossible.

Southern blight is a condition that can infect a tomato and can present itself in two ways which are white mold and stem rot. Southern blight is caused from a soil-borne fungus and it is common on a lot of vegetables and fruits but is mostly seen on tomatoes. A tomato can be affected with southern blight at any stage and it is usually caused by environmental conditions. Environmental conditions such as moisture and high temperatures are often seen in a tomato plant suffering from southern blight. A tomato with southern blight will often show signs if it is infected and will show various symptoms.

About

Growing a garden full of tomatoes is a wonderful time of the summer to look forward to. Tomatoes are fairly simple to grow, taste great and have many uses. When a fungus or disease begins attacking these wonderful plants it can sometimes be difficult to determine what is the primary cause of the attack as there are several different primary causes ranging from pests to a fungus. When you know the difference in the diseases it makes treating the plants much more manageable.

Southern blight is a fungus that affects several vegetables including tomatoes. The southern blight fungus begins in the soil and will attack the stems, roots, leaves and fruit of the tomato plant. The fungus Sclerotium Rolfsii is the cause of Southern Blight. The fungus begins growth due to warm and moist weather creating a dry rot of a brownish color followed by a white development of fungus in the soil, near the lower part of the stem. The fungus prevents the plants from getting water and nutrients absorbed into them.

The first symptoms of the disease include drooping, yellowing and wilting of leaves on the tomato plant. The fungus can be present in the soil for several years and progression of the disease will spread to row upon row of plants and will greatly affect the ripe tomatoes that are close to the ground. The tomatoes affected with southern blight will have a slimy feel and bad smell.

Spread

The southern blight fungus can spread in infested organic matter or it can be infested in the soil itself. The soil surface is usually where the infestation of the southern blight will occur but it can also occur underneath the soil. Southern blight fungus is very invasive and can actually spread three feet through the soil which makes other plants susceptible to this disease. A whole row of tomato plants can be killed within a matter of a few days if the fungus ends up spreading throughout the soil. The tomato plants will die and the next crop will be severely infested with southern blight as well. It is hard to control the spread of southern blight once it starts because it is so invasive and spreads very quickly in the soil. If you live in a warm or moist environment then it will make it that much harder to control the southern blight. The best thing to do to stop southern blight from taking over your tomato plant is to prevent it in the first place.

Symptoms

The first symptoms of southern blight will often appear in the tomato while it is above the ground and consist of yellow leaves and wilting. The stem which is near the soil will look sunken and will feel very soft to the touch. The stem will also develop brown and black sports on the inside and outside as well. If you live in a moist environment then the tomato will have a white fungus growing on it near the lower stem. The white fungal growth can also be seen on the tomato if it is in contact with the soil and it will show up on crop debris surrounding the soil. If you think your tomato plant is infected with southern blight then there is a simple test you can do. Simply place a part of the lower stem in a paper towel that is wet and then place it inside a closed plastic bag. Keep it in there for 24 hours and then see if the white fungus develops, and if it does then you know your tomato plant has southern blight.

The initial symptoms of southern blight is a rapid wilting of the entire plant. A water-soaked lesion on the stem near the soil line rapidly expands, turns brown, and girdles the stem. A white mold (mycelium) eventually covers the stem lesion and surrounding moist soil. Small, uniformly round structures about 1/16 inch in diameter, called sclerotia, form on the mycelium. Sclerotia are first white, later becoming brown, and resemble mustard seeds. The presence of the white mycelium and sclerotia at stem base of afected plants are very useful characteristics for identifying southern blight. The fungus survives in the soil as sclerotia which may build to high numbers when susceptible plants are cropped repeatedly. After sclerotia germinate, the fungus must first colonize organic debris near the soil surface before the fungus can cause infection. The disease is favored by high humidity and soil moisture and warm to hot temperatures (85-95 F).

Prevention

When southern blight is first noticed or there are only a few plants scattered throughout the garden that have been affected, remove the plants that have been affected as well as the soil around them. When removing the soil there should be a minimum of six inches both in depth and surround the plant removed. Also rotating the crops that have not yet been affected by the fungus may prevent them from getting the disease.

Once the fungus is in the soil it may be difficult to control but, southern blight can be prevented in the next crop planting if proper measures are used. When planting begins, wrap the stems of the tomato plant with a small piece of aluminum foil in soil that has be replaced with un-diseased soil. Plant the tomato plants wrapped in foil two inches above the ground with approximately two inches above ground. When watering or cultivating, try to avoid getting any of the soil on the foliage as well. Caging or staking the tomato plants will also help to prevent southern blight and using mulch as a protective barrier may also be helpful and keep the garden weeded as well as removing dead leaves and etc. that may blanket the fungus causing it to spread.

Control

Southern blight is difficult to control when conditions favor the disease and when numbers of sclerotia in the soil are high. Crop rotation with a non-susceptible grass crop such as corn is the most effective means of reducing numbers of sclerotia and resulting indicidence of southern blight. Avoid planting tomato following a very susceptible crop such as peanut. Plant residues should be thoroughly incorporated into the soil prior to transplanting so that their presence on the soil surface does not encourage southern blight development. Side-dressing with ammonium nitrate rather than other forms of nitrogen and use of a soil fungicide at transplanting may provide some control. Please contact your local county extension office for current information. Here are some steps given to control the disease:

Non-chemical control

If you have tomato plants then you should rotate it with other crops such as cotton or corn to help stop the disease from infesting the tomato plants. You also want to make sure that you do not plant the tomato plant in the same location more than once in five years to ensure the soil is safe and not infested with southern blight. Plowing the soil very deep can also stop the infestation of southern blight and it can bury the old tomato plant debris. Planting your tomatoes further apart can also help stop southern blight from occurring because the plant will be getting more air and ventilation which can stop the moist environmental conditions. The planting of the tomatoes further apart can also help an infected tomato plant and will keep it from spreading to other plants and invading the soil. If you really want to make sure that southern blight does not take over, you can fumigate your soil which can stop the disease from spreading. Soil fumigation will not rid the soil of the southern blight but it can help control the disease and make it harder for it to spread through the soil.

Chemical control

There are many good fungicides available that will help to prevent the southern blight as well. When using a fungicide they can be sprayed or dusted , however the spray is usually more affective than a dust. For the most effective type of fungicide for southern blight in your area it is recommended that you visit a local garden store for suggestions of a fungicide that will work best in a particular part of the country.