Bacterial Wilt in Tomatoes: Identification and Prevention
Bacterial Wilt can be a garden nuisance for tomato plants. So how do you know when your tomatoes have this disease? In this article, gardening expert Jenna Rich shares how to identify bacterial wilt, as well as how to prevent it from happening and treat your plants when it does.
Bacterial wilt is a disease that can have devastating effects on your tomato plants and across your garden. It can also be easily mistaken for other diseases.
It’s important to be able to identify bacterial wilt, so you can ensure you aren’t dealing with a different issue that requires a different form of treatment.
Here, we are going to discuss how to identify bacterial wilt, differences between other common tomato diseases and what you can do to prevent it in your garden.
Bacterial wilt (sometimes referred to as Southern Bacterial Wilt) is a vascular bacterial disease caused by the bacterium Ralstonia solanacearum (R. solanacearum). It is a soil-borne disease that can infect plants if:
- It is already present in the soil.
- The plant is wounded during transplanting.
- The disease-causing bacteria can travel easily into the roots and infect the plant.
- Carriers such as root-knot nematodes or certain insects (such as cucumber beetles) cross paths with your crops.
- Nearby weeds are infected and spread the disease.
The bacteria inhibits normal water and nutrient uptake by clogging vessels as it multiplies. Eventually, all the plant’s vessels are clogged, so it can no longer take in any water or nutrients, ultimately leading to death.
Once plants are injured and infected, they begin to release R. solanacearum into the soil. This disease can have deadly results on both young and mature plants.
A key difference between bacterial wilt and many other common tomato diseases is that bacteria cause bacterial wilt, whereas a fungus causes many others. It can be easily mistaken for a handful of other diseases, so it’s important to know what to look out for.
The main thing to look for is where the infection begins. For the most part, other tomato diseases begin to show symptoms on the lower part of plants, jumping up from the soil by way of water splash or passing from plant to plant by foliage touching. In contrast, bacterial wilt shows symptoms first at the top of the plant and works its way down.
Overall health, age, soil type, nutrients present, and environmental factors play a role in how quickly bacterial wilt can spread.
In Mature Plants
Mature plants can be infected or begin to show symptoms in peak season when your plants are full of fruit. You will notice wilting and withering of the youngest leaves near the tops of the plants. Leaves at the furthest point from the main stem might start wilting first, causing you to suspect your plant simply needs to be watered, making it hard to diagnose without experience. No amount of water would fix this wilt.
You may see brown cankers along the stem or notice your plant is not growing above a certain height. Sometimes root rot will develop near the base of the plant. There may not be any spotting or discoloration; the plant may just wilt and wither away.
Two characteristics to look for when trying to diagnose bacterial wilt after plants have perished:
- Brown decay would be noticeable inside the stem if you were to cut it open lengthwise
- A milky substance will flow from the cut site when placed in water
Bacterial wilt can affect solanaceous (nightshade) plants such as tomatoes, potatoes, tobacco, eggplant, and peppers, as well as ornamental flowers including (but not limited to) petunias, dahlias, marigolds, geraniums, nasturtiums, and zinnias. It is believed to infect about 200 host plant species in over 30 plant families.
If you have the space, try planting these crops far away from one another, or consider growing some in containers.
Bacterial wilt thrives in tropical conditions when temperatures are at or above 85°, and it develops more quickly in moist soil. For this reason, Southeastern parts of the US are usually at high risk of this disease. Once present, this pathogen is persistent and quick-moving.
While plants often recover slightly at night when temperatures cool down, they will wilt again the next day when conditions improve.
R. solanacearum, the bacteria that causes bacterial wilt, is soil and water-borne. It is not known to travel from plant to plant by way of foliage touching or by wind.
One stage of this bacteria’s life cycle is on a plant’s exterior, but it does not raise much concern since it does not survive for very long when conditions are not ideal.
Bacterial wilt can spread in several ways:
- Contaminated plants infect soil, leading to potential spread to other plants nearby by way of the root system
- Contaminated water source, irrigation/rainfall-runoff, or overhead watering
- Contaminated harvesting tools and farm machinery
- Insects such as cucumber beetles carry the bacteria in their bodies after feeding on infected plants. As they feed on unaffected plants, they create wounds through which the bacteria can enter and infect the vascular system of the healthy plant, causing infection.
- Unfortunately, some plants can have R. solanacearum present but not show any symptoms. They can spread the disease without giving you a reason to suspect infection.
R. solanacearum can live on organic matter without a host plant in the soil for days to years.
Although you can (and should) remove plants known to be infected with bacterial wilt, you cannot remove the bacteria causing the disease from the soil. All you can do is remove the infected plants and hope your remaining plants are healthy.
Pro tip: Do not add infected plants to a compost pile, as R. solanacearum could survive in the pile. Throw them away, place them in a plastic bag and leave the bag out in the sun, or burn them where and when you are permitted to.
Below are some things you can do to try to avoid a bacterial wilt infestation.
Take Care During Transplanting
Small wounds caused by rough handling during transplanting and general root breakage can cause plants to become more susceptible to entry of R. solanacearum. Once the bacteria have entered through the root system, they will multiply, causing total blockages of vital vessels, leading to the inability to uptake water and nutrients. This will lead to a plant’s ultimate demise.
Be sure your soil is well drained, as high moisture content + warm temperatures are ideal for bacterial wilt infection.
Deter Damaging Nematodes
Pest nematodes, specifically root-knot nematodes, can cause damage to the roots of your new plants, allowing an entryway for R. solanacearum. Some experts believe certain cover crops planted in fields during the off-season and trap crops near your tomatoes can help deter nematodes.
In northern regions, corn and grains are good options, whereas in southern regions, crops such as marigolds, some varieties of chrysanthemums, and rapeseed, to name a few, could deter nematodes that may cause bacterial wilt.
You can also try resting certain areas of your garden each year to help keep nematodes away. Some experts believe if there is nothing there for them to feed on, they may vacate the area or die off completely.
Pro tip: Consider solarizing the area of your garden affected by nematodes to kill them off. To solarize, cut old greenhouse plastic or a 6+ mil silage tarp to the size of your garden and cover it tightly for a few weeks or months. Temperatures of the soil should become hot enough to kill any nematodes present. Remember that during this process, you may also kill some beneficial insects, including beneficial nematode species.
Source Plants From Reputable Sources
Many tomato plants are transported to northern regions and parts of Canada from Southern states (mainly Florida and Georgia) as their climate allows them to start seeds earlier. Typically these plants are grown in greenhouses which sometimes feature overhead watering. Overhead watering and water runoff are great for disease spread.
Also, because bacterial wilt is more prevalent in southern states, it is not uncommon to discover transplants from these southern states are infected with the disease upon arrival.
It is a good idea to research companies before you purchase plants from them. Ask them about their growing practices and preventative techniques to be safe.
Keep Gardens Tidy and Tools Sanitized
Any time you are in your garden to prune, be sure to practice proper sanitizing of your tools afterward to avoid any potential disease spread. Grab a Clorox® wipe or spray your pruning shears with a 70% isopropyl alcohol solution and wipe clean.
Remember, when you prune, you are wounding your plants, making them susceptible to diseases. Taking care that your tools are sanitized after each use should give you some peace of mind when grabbing them for the next pruning session.
You should also have a weed suppression plan for your gardens, as several weeds can spread this bacteria to your cash crops. Consider mulching during production and cover cropping in the off-season to help keep weeds to a minimum.
Select Disease-Resistant Cultivars
You can select cultivars more resistant or tolerant of bacterial wilt than others. On many seed company websites, you can filter for specific disease resistance. Below are a few examples of these cultivars bred for bacterial wilt resistance.
Pro tip: Look for seeds that are indicated as “nematode resistant” or “bacterial wilt resistant.” Pest nematodes can cause damage that opens crops up to a slew of diseases, bacterial wilt being just one of them.
Tough Boy F1
Neptune – determinate early, not bothered by nematodes or humidity, great heat tolerance
Tropic Boy – indeterminate, tropical variety
Shin Cheong Gang F1
*Resistant to the nematodes which can open up your plants to bacterial wilt
Remember that you may still experience bacterial wilt even when growing a resistant cultivar. The resistance bred into these cultivars makes the plants more tolerable but will not 100% prevent disease. Also, resistant cultivars may produce fruit that is smaller than expected.
Did you know? Rootstocks are bred for disease resistance and should only be used to graft. When tomato seedlings are cut and spliced (grafted) to rootstock, the scion (the fruit-producing) variety can produce higher yields, grow more vigorously, and have increased disease resistance!
Practice Crop Rotation
Since R. solanacearum lives in the soil, it is important to practice proper crop rotation to try to prevent a new infection each year. If you have an infected plot, avoid planting nightshades or solanaceous plants there for at least 3 years. You could try growing in containers for a few years if you have limited space.
If you grow in pots or raised beds and find your plants affected by R. Solanacearum, you can and should get rid of the soil and start fresh. Do not compost or reuse this soil; the disease could be harbored in the compost pile.
Look Over Your Plants Frequently
Walk through your tomato patch often, especially when conditions for bacterial wilt are ideal. If you see anything suspicious, confirm the disease and take action immediately to avoid a full garden infestation.
|Verticillium and Fusarium species
|Starts at the top and works its way down the plant
|Works slowly throughout whole plant, creating more uniform symptoms
|How organism causes wilt
|Blockage of vessels due to multiplication of bacterial cells causes plant to be unable to intake water or nutrients
|Toxins formed in plant cause wilting effect
|Means of travel
|Soil, seed, wind, and water bourne
|It can be transferred through water, air, foliage, and soil
|How it spreads
|Enters by way of root openings or wounds, sometimes caused by nematodes
|Can be transferred through water, air, foliage, and soil
Are Organic Sprays Effective?
Unfortunately, at this time, there are no effective chemical treatments and no way to get rid of bacterial wilt once it is present in your plants. Your best bet is to remove the infected plants and soil. A few biofungicides claim to be effective against bacterial strains as well, but once the bacteria enter the plant, these just aren’t very effective.
If you are growing in a home garden, your best defense is growing resistant cultivars in combination with good land stewardship and proper sanitation practices. Larger-scale operations might combine these practices with chemical control (referred to as integrated pest management), as there has been some success in decreasing bacterial wilt using all 3 of these practices.
While there are no known treatments for bacterial wilt once it is present, you can do a few things to keep your garden safe from this nasty soil and waterborne disease.
Only buy your plants and soil from trusted and reputable sources. Do your best to deter root-knot nematodes and other potential disease-carrying insects. Practice crop rotation, experiment with cover cropping, burn any infected plants, and definitely reach out to your local Extension Office.