Tomato Diseases: How To Fight Tomato Pith Necrosis

by Matt Gibson

About Tomato Pith Necrosis

Tomato pith necrosis is caused by bacterial pathogens Pseudomonas corrugata, P. viridiflava, Pseudomonas spp., and Pectobacterium carotovorum, most commonly by P. corrugata, a weak pathogen that can infect tomatoes that are growing too fast. Pith necrosis is not limited to tomatoes alone, and can affect peppers and other vegetable or ornamental plants, but is most commonly found in tomatoes.

Symptoms of pith necrosis begin to occur when fruit is nearly mature green. Pith necrosis is caused by high nitrogen fertilization. Other causes include cool nighttime temperatures, low humidity, and plastic mulch. The disease developed in Long Island, where nitrogen was applied at a high level in the high tunnel. Unfortunately, there is no way to treat pith necrosis once it has infected tomato plants. The only way to manage the disease is through prevention by avoiding conditions that favor the pathogen, specifically excessive nitrogen. Copper fungicides and organic fungicides are unable to kill the bacteria, as the soil borne bacterial pathogens are already inside the plant.

Causes And Symptoms of Tomato Pith Necrosis

The bacterial pathogens that cause pith necrosis can survive in infected plant debris and soil. They may also be brought into the garden on infected seeds or transplants. The bacteria can be spread by worker’s hands, on pruning tools, or by splashing rain or irrigation. In order to enter, the bacteria needs for the plant to have a wound, or natural opening to pass through to start the infection. Favorable environmental conditions include high humidity, low light, and a large temperature difference between day and night. In overly wet conditions and in soils with a high nitrogen content, pith necrosis bacterium is likely to be present.

Mature tomato plants may start to show symptoms of pith necrosis in the mid to lower stem. First signs of infestation is brown discoloration and necrosis of the pith, which leads to hollow chambers developing in the stem, and pith browning extends upward through the stem as the disease develops. Where the pith is affected, profuse adventitious roots develop. Sometimes, dark brown or greyish legions appear on the surface of the stem. In the final stages of the disease, affected plants may begin to wilt and turn chlorotic.

Treatment and Control of Tomato Pith Necrosis

The only way to fight against pith necrosis is through preventative treatment. Provide adequate ventilation to avoid high humidity levels. Avoid high nitrogen levels to lower vigorous plant growth. Incorporate organic material and crop debris to promote faster decomposition of residue and associated bacteria. Practicing regular crop rotation can also help keep pith necrosis from becoming an issue.

Unfortunately, there are no effective chemical controls or pesticides for this disease. Affected plants sometimes recover if environmental conditions improve quickly, such as a sudden influx of lots of sun and warm weather. Burn or discard all affected plants and plant debris after harvest, or once the plants have been compromised.

Commonly Asked Questions About Tomato Pith Necrosis

Can I eat tomatoes that have tomato pith necrosis?

There is nothing to suggest that it would be dangerous to eat tomatoes that are infected with tomato pith necrosis, according to a Master Gardener from University of Minnesota Extension. However, the tomatoes may not be as tasty as healthy ones.

How do I treat or prevent tomato pith necrosis?

Pesticides aren’t effective in fighting tomato pith necrosis, so gardeners must rely on preventive measures, also called cultural control. Avoid having a buildup of excess nitrogen. Don’t work in the garden when plants are wet from rainfall or morning dew. Be careful to clean up debris from infected plants, from produce to foliage to roots, and dispose of it properly. Take steps to lower the humidity in your garden, such as putting plenty of space between plants, staking and pruning plants properly, and utilizing vents. Sterilize all the equipment you’ll use in the garden, including tools, gloves (or your hands), stakes, ties, and trellises. Avoid planting too early in the spring, when the weather is still cool and wet.

Is tomato pith necrosis contagious?

Tomato pith necrosis is contagious among plants. The bacteria responsible for tomato pith necrosis spread from garden to garden and plant to plant through a variety of means. These include infected seeds or plants, rainfall or irrigation, and tools and equipment (including the hands or gloves of those working in the garden).

What are the symptoms of tomato pith necrosis?

Tomato pith necrosis is often confused with bacterial canker, and its signs tend to appear when fruit is immature and green. The symptoms of tomato pith necrosis include discoloration and yellowing of new growth, wilted foliage at the top of plants, brown or gray lesions that cause stems to split or collapse, and necrosis of the pith that comes along with cavities and brown discoloration and spreads up the plant. The stems may also turn black, become hollow, appear swollen, or show an excess of adventitious roots. If you split a stem open, you may see formations that resemble ladders. It’s rare for the tomatoes themselves to show symptoms, but when they do, you’ll notice a black area at the bottom of the fruit that’s waterlogged and greasy. Infected plants tend to be distributed randomly, scattered through the field or bed.

What causes tomato pith necrosis?

Tomato pith necrosis is caused by bacteria called Pseudomonas and Pectobacterium caratovorum, which are transmitted in the soil and debris from infected plants. The bacteria find their way into plants and crops through broken skin or natural openings. Certain factors can increase the risk of this disease, such as major difference between daytime and nighttime temperatures, high humidity, prolonged overcast skies, excess irrigation, and high levels of nitrogen. Tomato pith necrosis can also enter your garden through infected plants or seeds, water splashing from rainfall or irrigation, and the hands, gloves, or equipment of gardeners.

Which plants are affected by tomato pith necrosis?

In addition to tomato plants, pith necrosis can also strike pepper plants along with other vegetables and ornamental plants, such as cranesbill geranium and chrysanthemum.

Want to learn more about tomato pith necrosis?

University of Massachusetts Amherst covers Tomato, Pith Necrosis

Cooperative Extension covers Pith Necrosis on Tomatoes

Cornell University covers Pith Necrosis on Tomatoes

Ohio State University covers Tomato Pith Necrosis

Plantwise Knowledge Bank covers Pith Necrosis on Tomatoes

Horti Daily covers Bacterial Diseases of Tomatoes

University of California Agriculture and Natural Resources covers Tomato Pith Necrosis