Tomato Pith Necrosis: ID, Prevention, and Treatment
Tomato pith necrosis is a deadly pathogen caused by several species of bacteria. It commonly infects greenhouse-grown tomatoes but can also spread to tomatoes growing in open fields. Learn how to identify, prevent, and treat this disease with this easy-to-follow guide.
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Tomatoes are sun lovers! They’re the perfect crop to grow during the summer months. High temperatures, direct sunlight, and dry weather promote rapid, healthy growth from tomato vines. When conditions differ from what they prefer, your plants may experience setbacks like tomato pith necrosis.
As the name implies, this bacterial pathogen infects the pith, or central portion, of tomato stems. It turns white, living cells into dead, brown ones. The plants may persist as the infection spreads, though they’ll eventually succumb to the disease if it spreads to the lower stems.
More often than not, rapid growth replaces the dead piths before the bacteria spread too far. Correcting the growing conditions can help get your plants back on track. If you notice yellowing leaves, roots sprouting from aboveground stems, and weak growth, it’s a good idea to check your plants for symptoms of necrosis.
What Is It?
Tomato pith necrosis is a bacterial condition caused by many different species. The most common species are from the Pseudomonas genus, though many other unidentified types can cause the condition. They’re widespread, affecting tomatoes throughout the U.S. and the world!
Though deadly, the bacteria are incredibly seasonal and often die down as summer warmth and sunshine arrive during the growing season. Healthy, strong plants can overcome the disease by sprouting new roots and stems that outpace the bacterial growth.
Bacteria thrive in various conditions depending on their life cycle. The types that cause necrosis prefer moist, warm, and humid environments to thrive. They’re common in spring and fall outdoors, and year-round in greenhouses and hoop houses.
How Does It Spread?
Necrosis spreads from infected tissue to new, healthy plants. It can overwinter on old debris or enter the garden on infected seeds, seedlings, and soil particles. It can also spread when irrigation water splashes soil onto plants. Often, contaminated equipment disperses it from infected plants to healthy ones during pesticide spraying, harvesting, or irrigation.
Once the bacteria are in the area, they invade healthy specimens through cracks and wounds on their stems, fruits, and roots. They’ll spread throughout the pithy interiors, turning them from fleshy to mushy.
The disease spreads annually when infected debris overwinters. The pathogens can spread from old plants to new ones through dead roots, stems, and leaves. They also persist on seeds. Practice careful cultivation, and ensure any plants you bring into your garden are disease-free.
Where Is It Prevalent?
Pith necrosis is most prevalent in greenhouses, hot houses, and hoop houses. It thrives in the excess moisture, high humidity, and cramped conditions common to these spaces.
The disease is also prevalent in sites with excess nitrogen. The nutrient causes rapid, unchecked, and weak tomato growth that’s more susceptible to necrosis than tough and sturdy plants. Use a well-balanced organic fertilizer, and apply it according to the package’s instructions to avoid adding too much.
Necrosis appears in outdoor fields during sustained periods of cloudy, humid weather. A lack of sunlight and too much moisture create the ideal breeding grounds for the bacteria. This is why they’re common in fall and spring when the weather is cool, mild, and wet.
Manage Tomato Pith Necrosis
Managing the disease is quite difficult, and prevention is key to growing success. It’s smart to practice safe growing practices to prevent necrosis from arriving in your garden. Once you know the warning signs, you can detect them early on and prevent unnecessary infections.
Identify
Identification is crucial in detecting necrosis. It hides inside tomato stems in the early stages of infection; as it spreads, detection becomes easier as outward symptoms grow more common. Yellow leaves, black streaks on the stems, and cracking or weak stems are possible signs of pith infections.
If you suspect the disease is present, cut a tomato stem off and slice it in half. If it’s infected, the interior will have brown, mushy, and hollowed-out portions. The rot will look like it’s spreading upwards and downwards into other parts of the plant.
Adventitious roots are another common sign of the disease. They’re aerial roots that sprout on the exterior of tomato stems. They’ll form above and below infections, especially in gardens with excessive moisture. Fruiting specimens will also have soft, rotting portions on their tomatoes.
If you’re planting a field of tomatoes, the infections will be sporadic throughout the site. You won’t have lines or rows of infections; instead, you’ll see a few plants suffer in random locations.
Prevent
Prevention is the best way to keep this nasty condition from your tender tomatoes! One good prevention practice is to grow tomatoes at the proper time. Rather than planting them early in spring, wait until sunshine is abundant and temperatures are high in late spring and early summer.
Early plantings are susceptible to bacteria, especially when nighttime temperatures sit below 50°F (10°C). Wait until nighttime temperatures rise above 50°F, and avoid planting seedlings when cloudy, wet weather is common.
Overapplying nitrogen fertilizer can also cause a rapid spread of the necrosis bacteria. Consider using a soil testing kit to determine the nutrient levels in your soils, then apply the proper amounts of fertilizer that tomatoes require. Blindly adding nitrogen has other unintended effects, like aphid infestations and fewer flowers and fruits.
One of the most important ways to prevent pith necrosis is to ensure your indeterminate types are staked and supported throughout their life cycle. This keeps the foliage away from weeds and soil that may be infected, preventing some of the potential for the disease to spread.
Treat
Treating tomato necrosis is impossible, as there is no proven cure! Mitigation, control, and prevention are the best ways to mitigate the negative effects. Though they may kill weak seedlings, tomato plants often outgrow the infections and replace the dead stems with new ones.
To mitigate the spread, pull up and destroy any plants with visible signs of infection. There are three ways to dispose of the infected debris: hot compost it for months in a pile away from the growing site, bury it a foot or deeper underground, or dispose of it in your trash or green waste bin.
Removing weeds, mulching with compost, and ensuring there’s proper air circulation will go a long way in mitigating necrosis. The healthier your plants are, the more resilient they’ll be towards necrotic conditions.
If treatment doesn’t work this season, consider practicing crop rotation next year. Remove all tomato and pepper plant debris from the growing site, and plant seedlings in new locations next spring. Wait three to four years before planting tomatoes in the original growing site.
Frequently Asked Questions
What is stem pith disease in tomatoes?
Stem pith disease is another term for tomato pith necrosis. The two terms refer to the same condition.
What are the symptoms of tomato pith necrosis?
Watch for weak stems, adventitious roots, yellow leaves, and black streaks on the stems. Swollen tomatoes may have soft, mushy spots.
Are tomatoes with soft spots safe to eat?
Generally, it’s okay to cut out mushy portions and eat the rest of the tomato. So long as the fruit is firm, red, and good-smelling, it should be safe to eat. If moldy or mushy symptoms are present throughout the tomato, compost it or throw it out.
