Xanthomonas Campestris: What It Is and How to Control It

Xanthomonas campestris is a rod-shaped bacterium that includes the cause of black rot, a disease of cabbage, broccoli, cauliflower, kale and other brassicas. The pathovar that does the damage is Xanthomonas campestris pv. campestris, or Xcc. NC State Extension calls it the main pathovar behind black rot, and the University of Connecticut calls the disease the most common and destructive one of the cabbage family worldwide. The same name also appears on the label of xanthan gum, which comes from a harmless strain grown in a fermenter.

This guide explains what the bacterium is, how to spot black rot, what it has cost growers on record, and seven controls with the numbers that university and government sources give for each. It also covers the leaf-spot and canker diseases that older texts file under the same species name, and it includes a spray cost calculator you can fill in with your own prices. Always follow the product label and your local rules for any spray, and ask your state or provincial extension office what is registered where you farm.

What Xanthomonas campestris is

The genus Xanthomonas holds many plant-pathogenic bacteria. A 2025 study in Microbiology Spectrum says the genus causes over 400 different plant diseases across crops such as rice, wheat, citrus, tomato, pepper and cabbage (Microbiology Spectrum, 2025). Within the species X. campestris, the pathovar campestris attacks brassicas. A pathovar is a group of strains that attack one set of host plants.

Xcc is not one uniform enemy. A 2022 paper in Frontiers in Microbiology states that Xcc is divided into 11 races, and that races 1 and 4 are seen as the most widespread worldwide (Frontiers in Microbiology, 2022). The same paper says breeding for resistance is hard because each race reacts differently with each brassica genotype. So one resistant variety may not cover every strain.

Two other points help when you search or read older material:

• Other pathovars on brassicas. NC State Extension notes that other X. campestris pathovars also cause leaf spots on brassicas, but pv. campestris is the main cause of black rot (NC State Extension, 2022).
• Xanthan gum. The US food additive rule for xanthan gum describes a gum made from X. campestris by pure-culture fermentation, using a strain that is nonpathogenic and nontoxic, and the finished additive is processed so that it has no viable cells (21 CFR 172.695). It is the same species name, not the same risk.

Black rot: how to recognise it

Black rot starts at the leaf edge. NC State Extension describes yellow, V-shaped lesions that point toward the base of the leaf, followed by wilting and dead tissue (NC State Extension). Look inside the yellow V for veins that have turned dark. Blackened veins are the clue that separates black rot from drought stress, overwatering or too much fertilizer, which can look similar from a distance.

Three checks help you be sure before you spend money on a spray:

1. Hold the leaf to the light. The Pacific Northwest handbook says infected veins show up as a black net against a strong light (Pacific Northwest Pest Management Handbooks, revised March 2026).
2. Cut the stem. UConn says a crosswise cut of the stem, leaf stalk or veins shows a dark ring of vascular tissue (UConn IPM, updated 2023).
3. Look for bacterial streaming. If you have a microscope, NC State suggests placing a fresh piece of leaf that spans the edge of a lesion in water. After 3 to 5 minutes, a white stream of bacteria leaves the tissue if the plant is infected.

Lookalikes exist. NC State lists Fusarium and Verticillium wilt, which cause yellowing on one side of the plant or leaf but do not blacken the veins inside the lesion. For a firm answer, send a sample to your state plant diagnostic clinic. SDSU Extension notes that many soft rots and fungi move in as the plant dies, which makes late samples hard to read, so send plants that still show early yellowing.

▶ Verticillium wilt, one of the lookalike diseases: symptoms, treatment and control. · 14:46

When and how black rot spreads

Seed is the usual way in. NC State says infected seed is the most common source of inoculum in a field. Inside the field, splashing water and the movement of people and equipment spread the bacteria. They enter through water pores at the leaf margin (hydathodes) or through wounds from insects and handling.

Weather sets the pace. NC State and the Pacific Northwest handbook both give 80 to 86°F as the favoured range, with wet leaves from rain, dew or sprinklers. UConn gives 80 to 95°F for fast development. Symptoms often show more than a week after infection starts, and by then control is harder, according to NC State.

The bacterium also survives between crops. The sources differ slightly, which is worth knowing when you plan a rotation:

• NC State: 40 to 60 days in soil on its own, and up to 2 years on infected plant debris.
• The Pacific Northwest handbook and UConn: up to 2 years in plant refuse.
• SDSU Extension: up to 3 years on decaying plant material, and on brassica weeds such as shepherd’s purse.

Black rot losses on record

The Frontiers review gathers the best-known loss figures. Treat them as reports from different places and decades, not as an average.

• 1976, United States. About 70% of several million transplants from one seedbed were infected systemically, and losses were estimated at 1 million dollars.
• 1990s epidemics. Losses of 23% to 90% in susceptible brassica cultivars were reported in several countries (the review cites CABI, 2022).
• 2019, Georgia. Disease losses of about 35.4 thousand dollars were estimated, citing the University of Georgia plant disease loss estimates for 2019.
• New Zealand hybrid seed crops. Losses of 1.5 to 8.4 thousand dollars per hectare were reported.

These numbers show the pattern, not a forecast for your farm. A seedbed problem can spread to millions of plants at once, while a field outbreak depends on weather and on how far the bacteria had already moved.

Other Xanthomonas diseases and the names they go by

Older articles, including earlier versions of this one, file several diseases under X. campestris. Current names have changed, so check the pathogen name before you search for a control.

• Bacterial spot of tomato and pepper. UConn still names it Xanthomonas campestris pv. vesicatoria and says it is favoured by 75 to 86°F and high moisture (UConn IPM). The EPPO Global Database lists the pathogens behind bacterial spot as Xanthomonas euvesicatoria pv. euvesicatoria, X. euvesicatoria pv. perforans, X. hortorum pv. gardneri and X. vesicatoria (EPPO Global Database). Our guide to bacterial leaf spot control covers that disease.
• Citrus canker. The University of Florida names the cause as Xanthomonas citri subsp. citri. It says wind-driven rain is the main way the bacteria move, that winds above about 18 mph help them enter leaves, and that the entire state of Florida is under quarantine (UF/IFAS Florida Citrus Production Guide, 2026 to 2029).

The rest of this guide is about black rot, because the controls differ by crop and the black rot evidence is the strongest.

▶ Bacterial canker in tomatoes: symptoms, treatment and organic management. · 15:25

Seven controls compared

No single tactic holds up alone. NC State says the cultural practices are critical, that bactericides are only marginally effective once disease is established, and that symptoms often appear a week or more after infection begins. The table puts the seven controls side by side, in the order a grower would usually think about them: first what stops the bacteria arriving, then what limits spread, then what to spray.

The seven controls in detail

Each control below has its own section, with the numbers the sources give.

1. Clean seed and transplants

Start here, because infected seed is the most common source of the bacteria in a field. NC State advises buying certified disease-tested seed. The Pacific Northwest handbook notes that seed from Western States is generally clean of this disease, and UConn adds that most black rot epidemics it describes were introduced on infected transplants from the southern states, so it advises growing your own transplants or buying locally.

If seed health is unknown, hot-water treatment is a common step, though NC State warns it can kill the seed if done wrongly. The times differ by source and by crop, so confirm them with your seed supplier or extension office and test germination on a small lot first.

• UConn: 122°F for 25 minutes for cabbage and Brussels sprouts, and 20 minutes for broccoli and cauliflower (UConn and UMass, reviewed 2012).
• Pacific Northwest handbook: 122°F for 30 minutes.
• SDSU Extension: 122°F for 35 minutes for Brussels sprouts, collards and cabbage, and 20 minutes for broccoli, cauliflower, kale, kohlrabi, rutabaga and turnips (SDSU Extension).

Heat is not perfect. In an Australian trial, hot water at 50°C (122°F) for 25 minutes cut the bacteria recovered from artificially infected cabbage seed by a factor of about 10,000, but did not eliminate them, and the author warned that even low levels left after treatment can start epidemics (Minchinton, Agriculture Victoria for HRDC, report VG204, mid-1990s). The Frontiers review adds that physical treatments work on the seed surface but are not always effective against bacteria deep in the seed. UConn also warns that the bath must stay at an even temperature and that tomato seed lost germination in an older UMass test at 125°F for 30 minutes (0.5% to 59% by variety). No treatment is a reason to skip clean seed.

Chart

Hot-water time for cabbage seed at 122°F

Minutes recommended by three extension sources; check your own seed supplier and test germination first

2. Rotation

Rotation gives crop debris time to break down. NC State recommends a non-host crop for at least 3 years, and gives 3 to 4 years in its list of practices. UConn advises 3 years between cole crops. SDSU Extension suggests 2 to 3 years, especially if residues are worked in after harvest. The Pacific Northwest handbook gives 2 years for production fields and 3 years for transplant beds.

Rotation only works if brassica weeds are kept down, since wild mustard and shepherd’s purse can carry the bacteria between crops. If you farm a short rotation, lean harder on clean seed and sanitation. Our guide to raised bed rotation shows how to lay out beds so brassicas do not return to the same ground too soon.

Chart

Years out of brassicas, by source

Rotation interval each source gives; Pacific Northwest figure is 2 years for fields and 3 for transplant beds

3. Sanitation and weed control

The extension sources in this guide all list residue and weed control. NC State says to remove infected plant material promptly, to manage brassica weeds, and to sanitize boots and equipment when moving between fields. UConn adds that cole crop fields should be ploughed after harvest to speed decomposition of residues. SDSU Extension adds that infected plants should not be composted unless the same precautions are taken.

• Scout seedlings often and remove infected plants and their neighbours quickly (UConn).
• Use several smaller seedbeds from different seed lots instead of one large bed (UConn).
• Stay out of fields when foliage is wet (UConn and NC State).
• Clean tools after working diseased plants before handling clean ones (SDSU).

4. Resistant cultivars

NC State says that in fields with a history of black rot, resistant varieties can reduce severe symptoms, but some bacterial strains can overcome resistance, so black rot may still appear. SDSU reports the same pattern in South Dakota. Treat resistance as one layer.

The Pacific Northwest handbook lists three cabbage varieties as resistant (Bobcat, Defender and Guardian) and sorts 21 more by tolerance in a Cornell study: 6 with low tolerance, 10 with medium and 5 with high. UConn lists resistant cabbages (Guardian, Defender and Gladiator) and tolerant cabbage and broccoli varieties, and adds that tolerant varieties withstand less disease pressure than resistant ones. UConn also notes one Connecticut field of a tolerant variety that was severely infected. Variety lists change, so check current extension trial results before you order seed.

Chart

Cabbage varieties by black rot tolerance

Number of varieties in each class of a Cornell study, as listed by the Pacific Northwest handbook

5. Water and field handling

Because the bacteria need water to move, the way you irrigate counts. NC State advises avoiding overhead irrigation and handling plants when they are wet. SDSU Extension suggests drip irrigation or soaker hoses where possible, and wider spacing, which can slow many diseases. UConn recommends raised beds, which drain better and may reduce spread, particularly in seedbeds, and plastic mulch on raised beds to reduce water splash. It also advises against low, wet sites and against planting beside fields with crucifer weeds.

6. Sprays and biocontrol

Sprays are a support layer. NC State says products with the active ingredient acibenzolar-S-methyl are rated fairly effective if used preventatively, that copper products mixed with mancozeb can be used, and that copper and streptomycin resistance is known in this pathogen, so rotating products is important. For organic growers, NC State says fixed copper is somewhat effective if timed correctly and if copper-resistant strains are absent, and that it is better to treat when the weather favours the disease than on a calendar.

The Pacific Northwest handbook gives label examples. Acibenzolar-S-methyl (Actigard 50WG) is listed at 0.5 to 1 oz per acre every 7 days, not within 7 days of harvest. Copper products are listed on 7- to 10-day intervals, for example Kocide 3000-O at 0.5 to 0.75 lb per acre with a 48-hour re-entry period. UConn says fixed copper or copper hydroxide every 7 to 10 days may slow the spread in dry seasons. SDSU Extension warns that sprays do not affect the disease once it is established in a plant, and that avoiding excessive copper use limits resistance in Xcc. These examples are not a recommendation. Rates, intervals, harvest limits and registered products differ by state and country, so read and follow the label on the product you buy.

Biocontrol is still being tested. A 2025 Microbiology Spectrum study isolated a phage against Xcc that killed 99.9% of the bacterial population in the lab after 5 hours, and kohlrabi plants treated with it had far less necrosis than untreated plants in a greenhouse test. The same paper says only a few phage products exist for plant disease, and the Pacific Northwest handbook lists the efficacy of its biological products as unknown in Oregon. A 2022 study found that carvacrol, thymol and eugenol inhibited Xcc in the lab. In seed tests only carvacrol and thymol were tried, and the lower dose of each left Xcc counts in germinated plants almost 100 times above the controls, while the doubled dose cleared them. These are research results, not field programs.

7. Scouting and satellite monitoring

NC State warns that symptoms often appear more than a week after infection, so scouting should start before the disease is obvious. Walk the field edges and low spots after warm, wet spells, check seedlings, and sample suspicious plants. Satellite vegetation indices such as NDVI show where a crop is greener or weaker than the rest of the field. They cannot tell black rot from drought, waterlogging, a nutrient problem or wilt, so use them to decide where to walk first and confirm with the leaf, stem and streaming checks above.

The Farmonaut Satellite + AI Farm Monitoring System shows field-level vegetation maps through the Farmonaut mobile app and web portal. Teams that want the same data inside their own software can use the Satellite & Weather API, described in the API developer docs. A repeat map of the same field also gives you a record of where problems started in earlier seasons, which helps when you plan rotation.

▶ A walkthrough of satellite crop monitoring: reading NDVI and spotting crop stress early. · 19:36

Spray program cost calculator

Use this to compare the product spend of two spray programs on your own acreage. It does not model disease outcomes, labour beyond the per-pass cost you enter, or yield. The numbers it starts with are examples only.

Try the numbers for your own farm below.

What to do first

Put clean seed, rotation, sanitation and careful water handling ahead of any spray. Add resistant varieties where the disease has been seen before, and use sprays preventively and on the label. Scout often, sample early symptoms, and treat what the lab confirms.

Related pages on our site: bacterial leaf spot, product traceability, carbon footprinting, farm team management, crop loan and insurance records, farm monitoring, the iOS app, and the web app badge.

FAQ

What is Xanthomonas campestris?

It is a bacterial species that includes the pathovar campestris, the cause of black rot in cabbage, broccoli, cauliflower, kale and other brassicas. NC State Extension calls pv. campestris the main black rot pathovar. A nonpathogenic strain of the species is also used to make xanthan gum by fermentation.

How do you treat Xanthomonas campestris?

There is no cure for a plant that is already infected. SDSU Extension says sprays do not affect the disease once it is established. Growers prevent it with clean seed, rotation, sanitation, resistant varieties and careful irrigation, and may add preventive acibenzolar-S-methyl or copper sprays following the label.

What are the first signs of black rot?

Yellow, V-shaped patches at the leaf edge that point toward the base of the leaf, with dark or black veins inside the patch. Later the stem shows a dark ring when cut, and the plant may wilt or rot.

How long does the bacterium survive in a field?

NC State gives 40 to 60 days in soil on its own and up to 2 years on infected plant debris. SDSU Extension says up to 3 years on decaying residue. That is why sources suggest rotations of 2 to 4 years away from brassicas.

Is black rot the same as bacterial leaf spot or citrus canker?

No. They are separate diseases with separate crops, and the current scientific names for bacterial spot and citrus canker are no longer X. campestris. The controls overlap, mainly clean planting material and keeping leaves dry, but the crop-specific advice differs.

Can satellite images detect black rot?

They can show uneven growth or stress in a field. They cannot name the cause, so confirm any flagged area by walking it and checking leaves and stems, or by sending a sample to a diagnostic clinic.