Making Sense of Tomato Pith Necrosis

We recently identified tomato pith necrosis in our tomato experiment, and the diagnosis was confirmed by Penn State's Plant Disease Clinic . In our field, we found just four infected plants scattered throughout the planting.

Tomato pith necrosis often becomes noticeable around the time the first fruits begin to mature. Lower leaves may yellow and eventually turn brown. Branches or entire plants may wilt as the disease progresses. Brown to dark brown lesions may develop on stems. In some cases, these lesions can girdle the stems.

Symptoms can also include the development of clusters of roots along the stem with tomato pith necrosis. These often begin as small white root initials before becoming more obvious roots.

As the disease progresses, the pith tissue may break down, leaving hollow spaces or a ladder-like appearance known as laddering or chambering.

Similar symptoms can occur with other tomato diseases, including bacterial canker. Initially, we considered bacterial canker, caused by Clavibacter michiganensis subsp. michiganensis, as a possible diagnosis. When an affected stem is cut lengthwise, tomato pith necrosis primarily causes browning and breakdown of the tissue in the center of the stem, often progressing to laddering or chambering. In contrast, bacterial canker more often causes browning of the vascular tissue surrounding the center of the stem. In addition, bacterial canker frequently affects fruit, causing characteristic bird’s-eye spots, whereas the development of numerous small roots along the stem is a hallmark symptom of tomato pith necrosis.

Several species of Pseudomonas bacteria have been associated with tomato pith necrosis, most commonly Pseudomonas corrugata and P. mediterranea. These bacteria can survive in soil, crop debris, and possibly seed. They can spread by splashing water, contaminated tools, or other field operations. However, these bacteria are often present without causing symptoms. Environmental conditions appear to play a major role in symptom development.

High humidity, rapid plant growth, excessive nitrogen, cool nights, cloudy conditions, and large temperature swings have all been associated with disease development. This year’s combination of frequent rainfall, humid conditions, vigorous plant growth, and fluctuating temperatures may have created favorable conditions for tomato pith necrosis.

Because no resistant cultivars or effective chemical treatments are currently available, management relies on cultural practices. Matching nitrogen applications to crop needs, avoiding excessive irrigation, improving air movement, sanitizing tools, and avoiding field work when the plants are wet all help reduce risk.

Tomato pith necrosis does not always continue to worsen throughout the season. Plants showing severe wilting or stem collapse are unlikely to be productive and should be removed. After the last harvest, incorporating or removing crop residues, removing volunteer tomatoes, and rotating away from solanaceous crops may help reduce future problems.

References and Resources

• Jones, J.B., Zitter, T.A., Momol, T.M., and Miller, S.A. 2016. Compendium of Tomato Diseases and Pests, Second Edition. APS Press.
• NC State Extension. Tomato Pith Necrosis
• Catara, V. 2007. Pseudomonas corrugata: Plant pathogen and/or biological resource? Molecular Plant Pathology 8(3):233–244. 

This article benefited from AI‑assisted writing support (Microsoft 365 Copilot) to refine language and identify some sources.