Ask a Master Gardener: What Is Causing My Tomato Plants to Wilt?

By John Olive, Retired Director, AU Ornamental Horticultural Research Center, www.mobilecountymastergardeners.org

Q1: My tomatoes were growing well and suddenly, one plant wilted overnight. It is still green but not recovering. I have watered them, the soil is moist, but they are still wilted. What could have caused this and is it going to spread?

Tomato wilt diseases are common in Alabama with many common causes of wilt in the home garden. Bacterial wilt, caused by the bacterium Ralstonia solanacearum, is the most common. This bacterium lives in the soil and infects the roots. It moves up into the stem where it plugs up the vascular system (plumbing) and prevents water from moving up into the plant. The plants will suddenly wilt while remaining green. They appear to need water. They may recover by the next morning but eventually they remain wilted. If the plant is brown and wilted, it is not bacterial wilt.

To confirm bacterial wilt, you can cut off a 3- or 4-inch section of the stem at the soil line, rinse it off, and submerge the lower portion of the stem in a glass of water (see image). If bacterial wilt is the cause, you will see milky white ooze streaming from the lower stem. If not, the wilt is likely caused by something else. Tomatoes, eggplant, peppers, and tomatillos are all susceptible to this disease.

Unfortunately, there are no commonly available home garden varieties resistant to bacterial wilt, and no chemical controls either. If you have a plant with diagnosed bacterial wilt, it is best to remove it ASAP, along with roots and as much soil as feasible. Bag everything and send it to the landfill. Do not compost infected plants. To avoid spreading it further, rinse off the shovel and disinfect it with 10% bleach solution and rinse again with water. Avoid planting tomatoes or any other plants in the tomato family in the same bed. This bacterium can survive in the soil for years. Incorporating compost, leaves, or other organic matter can be beneficial in improving plant growth and encouraging competing soil micro-organisms and may reduce the potential for disease in future years.

Q2: Ok, I have another tomato plant that is wilting, but it is stunted and turning yellow, and the decline was more gradual than the other plant.

Other causes of tomato wilt include Fusarium and Southern blight. While these cause wilting, they have distinct symptoms which can usually be visually distinguished from bacterial wilt.

Southern blight (Sclerotium rolfsii) is a very common disease that attacks the lower stem near the soil and can cause plants to wilt. The fungus is visible as white fuzzy growth, with numerous small (1-2mm) round to oblong, white to reddish brown structures (sclerotia). These survival structures can last for years in the soil and make this disease very hard to control. Removing the plant as described above is helpful in reducing spread.

Fusarium wilt is caused by a fungus. It is very common in Southern soils and will infect susceptible tomatoes. Fusarium wilt is generally slower acting than bacterial wilt. Infected plants often start yellowing from the bottom and often only one side of the plant is affected. Eventually, the mostly yellow plant wilts and dies. If the lower stem is cut, there will be brown discoloration inside the stem, but it will not stream in water like bacterial wilt.

There are many common tomato varieties that are resistant to Fusarium and root knot nematodes. Selecting resistant varieties is the best way to avoid these diseases. The most effective way to control Fusarium wilt is to plant resistant varieties, and there are many Fusarium-resistant varieties available for home gardeners. Look for named disease abbreviations (FN) on seed packets or plant labels indicating resistant varieties.

Many heirloom tomatoes do not have resistance to common diseases and their increased popularity may explain why these diseases are becoming more common.

Although there are other possible causes of wilting tomatoes, these are the most likely.

Wilted tomato with bacterial wilt by John Olive

Tomato stem streaming bacteria by John Olive