By: Darcy Larum, Landscape Designer
With all the diseases that can infect tomato plants, it is a wonder that we ever get to enjoy their juicy, sweet fruits. Each summer it seems that a new tomato disease enters our region, threatening our tomato harvests. In turn, each summer we do our homework searching the internet and planning our disease battle strategy to ensure a full pantry of salsa, sauce, and other canned tomato goods. Continue reading to learn about treatment of tomatoes with bacterial canker.
About Bacterial Canker of Tomatoes
Tomato bacterial canker disease is caused by the bacteria Clavibacter michiganensis. Its symptoms can affect the foliage, stems and fruit of tomatoes, peppers and any plant in the nightshade family.
These symptoms include discoloration and wilting of the foliage. Foliage tips may turn burn and crunchy, with yellow streaking around the brown. Leaf veins may become dark and sunken. Leaves wilt from tip to branch and drop. Fruit symptoms are small, round raised, white to tan lesions with yellowing around them. Infected plant stems may crack and become gnarly with dark gray to brown streaking.
Bacterial canker of tomatoes is a serious systemic disease of tomatoes and other nightshade plants. It can quickly wipe out entire gardens. It is generally spread by splashing water, plant to plant contact or infected tools. The disease can survive in soil debris for up to three years and can also survive on plant supports (especially wood or bamboo) or garden tools for quite some time.
Avoid overhead watering of tomato plants to prevent the spread of tomato bacterial canker disease. Sanitizing tools and plant supports can also help prevent bacterial canker of tomatoes.
Control of Tomato Bacterial Canker
At this time, there are no known effective chemical controls for tomato bacterial canker. Preventative measures are the best defense.
This disease can run rampant in the Solanaceae family, which includes many common garden weeds. Keeping the garden clean and clear of weeds can prevent the spread of tomato bacterial canker disease.
Planting only certified disease-free seed is also recommended. Should your garden become infected by tomato bacterial canker, a crop rotation of at least three years with those not in the nightshade family will be necessary to prevent future infection.
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Managing Bacterial Canker in Tomato: Key Strategies
Bacterial canker (Clavibacter michiganensis pv michiganensis) is one of the most destructive and puzzling tomato diseases in Massachusetts. One grower sets out a vigorous crop of transplants that grows into healthy looking plants full of green fruit, only to see "marginal scorch" appear throughout the field and his yields decline despite regular copper sprays. Another has never had it on the farm before, and finds an outbreak that starts in one cultivar and spreads throughout the field. Another has had it for years, and can't seem to escape it no matter how many different strategies he tries.
Everyone would like a simple answer to the canker problem. There isn't one. However, in recent years we have seen some growers having more success in bringing this disease under control. Research at several universities is revealing more about how the pathogen may be arriving on the farm and what the critical practices are to keep it under control. This article will discuss new research results, as well as what we have learned from the UMass Tomato IPM program over the past four years.
Three key principles for preventing losses to bacterial canker can be summed up as follows:
- Use disease-free seed
- Control bacterial populations that may be present on the leaf surface of transplants in the greenhouse
- Plant into a clean field
Each of these protects your plants at a different stage of growth - and all are important.
Seeds as a source. The bacterial canker pathogen can be seed-borne, both on the surface of the seed and under the seed coat. Although seed companies take many precautions to produce disease-free seed and test seed for the presence of disease, it is possible for some commercial seed to be infected. The bacterial canker pathogen is more difficult to detect reliably than many other disease organisms. According to recent research at the University of Iowa, the limit of detection using standard testing procedures was 1:3,000 to 1:10,000 (one infected seed per 10,000).
One precaution that growers can take to improve the assurance that their seed is disease free is to use hot-water treated seed. Some companies offer hot water treatment as an option. It is also possible to hot-water treat one's own seed, but this must be done carefully with the proper equipment. See the fact sheet entitled, Preventing Bacterial Diseases of Vegetables with Hot-water Seed Treatment for further details.
If you are concerned about bacterial canker, do your best to ensure that all of the seed you start in your greenhouse is clean including the plants that are destined to be sold as bedding plants.
Greenhouses: what you can't see is what you get. Research at the University of Michigan has shown that: 1) the pathogen can move readily from infected plants onto clean plants in the course of regular greenhouse activities, and 2) carryover in the greenhouse from one season to the next may not be as important as was once thought. In one experiment, seedlings that carried systemic infections with bacterial canker were placed in known locations in a grid of transplants in the greenhouse. Watering was from hand-held sprinklers no special precautions were taken to prevent disease spread. Plants nearest the infected plants developed bacterial canker symptoms (wilting) and died in the greenhouse. Many other plants showed no symptoms in the greenhouse, but the bacteria could be found residing on the surface of the leaves. When these healthy-looking plants were set out in the field, they developed symptoms during the season and the yield losses were serious. This type of infection - bacteria that enters from the surface of the leaf through natural leaf openings or wounds - causes the "marginal scorch" symptoms that are so common in Massachusetts. Once the bacteria enter the plant - which could occur in the greenhouse or in the field - it can take anywhere from seven to 84 days for symptoms to appear.
The second part of this experiment was to leave the weeds and residue in the greenhouse over the winter, and put new, clean transplants into the house the following year. The second crop of plants did not develop symptoms either in the house or the field, and the bacteria were not found on the plants. Does this mean you should stop your greenhouse sanitation practices? No! It is important to use standard disinfectants to clean benches, trays, hoses, etc. But this may not be the most important source of the problem.
If infected plants are present, the movement of bacteria from one plant to another during normal watering, handling, and ventilating activities occurs readily.
Controlling the bacteria at this stage can prevent yield losses.Bacteria on the surface of transplants can be effectively controlled by sprays of copper hydroxide or streptomycin in the greenhouse.
In another experiment at the University of Michigan, Kocide 40DF®, alone or mixed with Dithane F-45®, or Agri-Mycin 17® was applied on a five-day schedule from the first true leaf stage until transplanting. Bacteria on leaf surfaces were effectively suppressed. Plants were not sprayed after being set out in the field. Yields of sprayed, exposed transplants were equal to clean plants that were grown in a separate greenhouse and had never been exposed to the bacteria. Unsprayed, infected plants had lower yields.
It is possible that a less intensive spray schedule would have similar results, but this was not tested. In an experiment conducted at UMass in 1994, weekly sprays of streptomycin on greenhouse-inoculated plants eliminated all bacteria on sprayed plants until mid July.
Using bactericide in the greenhouse means a lower volume of chemical is used compared to multiple copper sprays in the field. Check the label carefully for required REI and personal protective equipment.
Rotate your tomatoes to a different field. Setting clean transplants into a field where canker-infected tomato was grown the previous year will result in early infection with canker and reduced yields. This has been documented by research and by grower experience in Massachusetts.
Bacterial canker survives in the field as long as there is any infected crop debris. It lasts longer in debris on the surface than it does in buried debris, plowing after harvest will help to speed up the decomposition. Keep each field out of tomato (and related crops such as potato and eggplant) for two to three years.
We have seen outbreaks of canker where tomatoes are planted in rotated ground that is adjacent to last year's tomato ground. New fields should, as much as is possible, be located at a distance from last year's fields -- as far as possible given the choices available on your farm.
Prevention is cost-effective. All of these tactics focus on prevention -- ensuring that disease-free plants go out into a "clean" environment. Bacterial canker outbreaks in the field require regular sprays with a copper or copper/maneb mix, with limited success. Prevention strategies are both the least expensive and the most effective way to beat bacterial canker.
By: Ruth V. Hazzard and Robert L. Wick, University of Massachusetts Extension, Agroecology Program, Vegetable and Small Fruit Team.
Reprinted from: UMass Extension Publication #VegSF2-97.
Image from Ohio State University Extension Website
Reviewed by: T. Jude Boucher, IPM, University of Connecticut. 2012
Information on our site was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.
The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.
Tomato (Solanum lycopersicum)-Bacterial Canker
Cause The bacterium, Clavibacter michiganensis subsp. michiganensis , is carried in or on seed and survives in infected tomato debris, weed hosts, volunteer tomatoes, or on contaminated stakes or equipment. Handling seedlings and normal watering may spread the bacterium in seed flats. In the field, handling or pruning plants, using contaminated equipment, cultivation, and rain or irrigation water may spread the bacterium. Plants may be infected at any growth stage.
Symptoms Early in the disease, leaflets wilt (petioles remain turgid) and edges curl up or turn brown. Lower leaves turn down. It is common for leaflets on one side to wilt while those on the other side of the midrib appear normal. Later, affected leaves become brown, wither, and die. Open cankers may be evident on petioles and/or midribs. Stems may have longitudinal discolored streaks or cankers. Vascular tissue in the stem and petioles almost always is discolored yellowish to reddish brown. Discoloration is most pronounced at the junction of the stem and petiole. If the stem is broken, often the pith can be pulled out of it as a result of the vascular tissue deterioration. Fruit, when infected, have approximately 0.25-inch spots with raised brown centers and white halos. If plants are from infected seed, the entire plant may wilt and die or fail to set fruit. If transplants are infected at clipping, seedlings may not show symptoms until transplanted to the field.
- Use only pathogen-free seed and transplants.
- When producing transplants, use pathogen-free soil and flats. Sterilize flats with boiling water or steam, or disinfect with a 5-min. soak in a bleach solution (1 part bleach to 3 parts water). Clean flats to remove all organic matter before treatment.
- Disinfect pruners between plants, or snap off suckers with fingers instead of pruning with a knife.
- Disinfect stakes, trellises, and wires.
- Plant in pathogen-free fields, or use a 4-year field rotation.
- Eradicate solanaceous weeds such as nightshades and volunteer tomatoes.
- Do not plant in fields receiving irrigation or drainage water from severely contaminated fields.
- Do not handle plants when they are wet.
- Seed treatment with sodium hypochlorite. Wrap seed in a cheesecloth bag and soak with agitation 40 min. in 1.05% sodium hypochlorite (one part household bleach to five parts water). Spread out seed and allow to dry. Prepare fresh solution for each batch of seed.
- Agri-Mycin 17 at 200 ppm of streptomycin sulfate. Apply first at the first-true-leaf stage, then at least twice more at 4- to 5-day intervals. Note: Resistance to this product may develop quickly. 12-hr reentry.
- Badge SC (Group M1) at 0.75 to 1.8 pints/A and 0.5 to 1.5 Tbsp/1000 sq ft in greenhouses on 3- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use 48-hr reentry for all other applications.
- Firewall at 200 ppm beginning when seedlings are in 2-leaf stage and continue on 4- to 5-day intervals until transplanted in the field. 12-hr reentry.
- LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
- Double Nickel LC at 0.5 to 4.5 pints/A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
Clavibacter michiganensis subsp. michiganensis
Bacterial canker may occur in tomato as a primary (systemic) or secondary (foliar) infection and shows a wide range of symptoms.
Primary infections originate from infected seed or from invasion of the vascular tissue of young seedlings. Symptoms, which may not show up until several weeks after infection, initially appear as wilting and downward turning of the lower leaves. The wilting generally progresses upwards, unless the site of infection is in the upper part of the plant. Wilting is often seen only on one side of the leaf or one side of the plant. Plants may collapse and die, especially if infected at a very early stage. Generally, plants survive but are stunted, showing some or all of the symptoms described here, depending on their environment and stage of growth.
Tomato foliage infected with the canker organism has distinctive black leaf edges with no spotting on the interior of the leaves. Sometimes a thin yellow border is present between the dead leaf margins and healthy tissue.
If an infected stem is cut lengthwise, a light brown discolouration may be present in the vascular tissue, most noticeable at nodes and just above the soil line. As the disease progresses, this turns reddish-brown. Light coloured streaks are often visible on the outside of the stem. These may later darken and break open into cankers. With severe infections, a yellow ooze may exude from a cut stem when it is squeezed.
Fruit may develop relatively small spots with light brown centres, generally surrounded by a greasy white halo (3- 6 mm, 1/8- Вј in. in diameter). These are known as birdвЂ™s-eye spots. With bacterial canker lesions, this white halo generally remains as the fruit ripens, while in the case of bacterial spot, it disappears with time. Bacterial canker may also cause a darkening of the vascular tissue in the fruit. The fruit may show a black peppering at the vascular bundles within the fruit, all the way to the seed. This can result in visible yellowish strands from the stem to the seeds and internal infections in the seed.
With a secondary foliar infection, leaves develop brown-black margins with a thin, yellow (chlorotic) band. Leaflet edges may curl upwards. Fruit may show birdвЂ™s-eye spotting, as in a systemic infection. Secondary infections (no vascular system involvement) often have minimal impact on the crop, especially when initiated later in the season.
Often Confused With
Early Blight (Look for the dark concentric rings that indicate early blight.В Early blight lesions enlarge and become angular over time.В No birdвЂ™s-eye spotting.)
Bacterial Spot (Bacterial canker and bacterial spot fruit lesions may develop as spots surrounded by a greasy white halo. With bacterial canker, this white halo generally remains as the fruit ripens in the case of bacterial spot, it disappears with time.)
Infected seed is probably the major source for primary (systemic) infections. The bacteria can be present on the surface of the seed as well as within the innermost layer of the seed coat. This makes the canker organism harder to eradicate with seed treatments than the spot and speck pathogens.
The organism can also be introduced from infected crop debris, weeds hosts or volunteer tomatoes, and contaminated equipment. Infections spread through splashing water, wind-driven rain and the fine water droplets or aerosols producing during storms. In the field, bacteria transfer by machinery or workers is probably not as significant as in the transplant greenhouse where plant density is high and growth conditions for the bacteria are optimal.
The canker bacteria enter the plant through natural openings and wounds, including root wounds. Pruning or transplant clipping operations can introduce the bacteria directly into the vascular system, resulting in the more serious systemic infections.
Period of Activity
The time for concern is from plant emergence through to harvest. Warm, wet weather conditions with temperatures of 24- 32В°C (75- 90В°F) favour the spread of this disease.
Although bacterial spot and speck can cause lesions on leaf edges in some conditions, often dark brown to black leaf margins are an indication of bacterial canker.В Bacterial canker will not cause leaf spots like bacterial speck or spot, but can be found on the same plant with these diseases.
Early bacterial spot fruit lesions can appear whitish, resembling bacterial canker вЂњbirdвЂ™s-eyeвЂќ spots, but only bacterial canker fruit lesions retain the whitish appearance.
To confirm bacterial canker, choose representative plants showing early symptoms to send for diagnosis. Submit as much of the plant as is practical, or several plants showing a range of symptoms.
OMAFRA Publication 838, Vegetable Crop Protection Guide, provides information on pest diagnostic services in Ontario.
None established. Fruit lesions can reduce marketability, while defoliation can lead to poor colour development, poor holding or sunscald of fruit.