Anthurium and Xanthomonas
Every Anthurium grower is familiar with the destructive disease caused by the Xanthomonas bacterium. In most cases, the culprit is the bacterium Xanthomonas phaseoli pv. dieffenbachiae (Xpd). Synonyms for this microbe are X. axonopodis pv. dieffenbachiae and X. campestris pv. dieffenbachiae.
Anthurium can be infected by many different Xanthomonas strains. Some variants are mild and affect only a limited part of the range, while others are very aggressive, spreading rapidly and extensively. The bacterium can also remain latent (without symptoms) in the plant and emerge under favourable circumstances.
It may also persist latently within other genera in the Araceae family, many of which show little or no sensitivity. However, this still poses a serious threat to Anthurium cultivation if appropriate hygiene measures are not followed.
Optimal conditions
Xanthomonas enters the Anthurium plant through wounds in the leaf or stem, as well as through natural openings such as stomata and hydathodes (guttation pores). Plants under stress, regardless of cause, are especially susceptible to infection. Warm and wet conditions, in particular, promote rapid disease spread. The bacterium reproduces through simple division, producing large numbers quickly. Infection is greatly facilitated when water comes into direct contact with the crop, especially if leaves are damaged. Overhead irrigation, drain water and workers handling the crop can then further spread the bacterium to healthy plants. Xanthomonas is not airborne.
In this article, we discuss three strategies for combating Xanthomonas:
- Preventive measures to keep the bacterium out
- Curative measures to minimise the effects and spread of an infection
- Restarting a crop after infection and preventing recontamination
Preventive measures to keep the bacterium out
Make clear agreements with your supplier
The disease can be introduced easily through stem or tip cuttings. Even visually healthy plants may carry the bacterium. Establish agreements with your supplier on hygiene measures, transport conditions, inspections and the use of clean crates.
Treat the packhouse as a contaminated area
Carts, crates, transport equipment, animals (pets) and people all pass through without sufficient or guaranteed hygiene standards.
Enforce strict hygiene practices
Hygiene must be safeguarded on entering the greenhouse. Visitors should wear clean overalls and disinfect footwear or preferably use disposable shoe covers. Employees should ideally change into clean work gear on-site. Everyone entering the greenhouse, visitors and employees alike, should disinfect their hands. And household pets should never be allowed inside.
In cut-flower cultivation, it is advisable to use at least one clean knife per bed, stored in a protective sheath at the top of the path.
Avoid contact with related plants
Do not keep genera related to Anthurium on the premises, including Aglaonema, Philodendron, Caladium, Dieffenbachia, Spathiphyllum and other Araceae. If unavoidable, ensure there is no contact whatsoever with Anthurium crops, including through drain water. These plants can be latently infected without any apparent disease symptoms. Never introduce Anthurium plants from external sources into the nursery.
Disinfection
Disinfect drainage water by heating for at least 30 seconds at 90°C or by UV treatment with a minimum dose of 100 mJ/cm². Clean silos thoroughly at least once a year. Use hydrogen peroxide (H2O2) to prevent organic build-up in pipelines and silos. Also, prevent water influx and pest intrusion from neighbouring areas.
Inform staff and inspect all areas
Ensure staff are informed about disease symptoms. When in doubt, use specialised laboratories for broad-spectrum diagnostics—not only for Xpd but for the full range of plant-pathogenic Xanthomonas species. Since non-pathogenic species also exist, comprehensive testing is essential.
There are symptoms of Xanthomonas that are difficult to recognize, and there are also symptoms that are easier to identify. The link provides an overview of both hard-to-recognize and easy-to-recognize symptoms caused by Xanthomonas. This is a PDF file that can be downloaded and printed: Xanthomonas in Anthurium – Easily and Difficult-to-Recognize Symptoms.
Consistently monitor for weak links within the company that may break the chain of phytosanitary measures.
Barrier theory
- Barrier 1: from outside to shed
- Barrier 2: from shed to greenhouse
- Barrier 3: from greenhouse to bed/ section
At each barrier disinfection/ hygiene measures.
Curative measures to minimise the effects and spread of an infection
It goes without saying that if infection is confirmed, the preventive measures mentioned above remain vital. However, there are also a number of additional measures that can help minimise infection.
- Always work from clean to infected sections.
- Isolate contaminated plots or sections, for instance, by using foil up to screen height. Treat each compartment as a separate unit with its own hygiene protocols.
- Scout weekly for diseased plants and ensure staff accurately recognise disease symptoms.
- Remove infected plants in sealed plastic bags, including neighbouring plants and substrate, and take them off-site immediately. Notify the waste processing company about the infection so that appropriate measures are taken to prevent further contamination.
Activities
Perform work only on dry crops; avoid early mornings when condensation is present, as the bacterium can spread easily across large distances via clothing.
Separated water flows
Avoid reusing drainage water from contaminated areas to minimise the risk of recontamination.
Climate
The bacterium spreads easily through moisture. Do not use misting systems that moisten the crop (e.g., Lego sprayers) or use them only minimally to prevent stress.
Keep the crop as dry as possible with proper climate control and avoid dripping of the plants (guttation). Morning heating to dry the crop is highly recommended. Ensure root-zone temperatures remain lower than the rest of the plant to prevent root pressure and guttation.
Plants that are not growing well are more susceptible to bacterial infection. Therefore, avoid extreme climate conditions and elevated temperatures. Xanthomonas reproduces optimally at 30°C, while Anthurium easily becomes stressed at this temperature.
Fertiliser
Glutamine, a key nutrient for Xanthomonas, is released through guttation. The plant produces less glutamine if ammonium and nitrate-nitrogen levels are kept as low as possible. Omit ammonium nitrate from the fertiliser regime; liquid calcium nitrate is preferable.
Pest control
Direct control of the bacterium is not possible. Antibiotics (Fytostrep) and copper-based agents previously used to inhibit Xanthomonas are now banned in horticulture due to phytotoxicity and bacterium resistance.
Some plant resilience products can be used in practice, however, including:
For more information, contact the specialists at Plantosys: https://www.plantosys.com/en/
Crop Protection
For regular (chemical) crop protection, switch from conventional spraying to space treatment methods such as fogging or LVM (Low Volume Method). Conventional spraying moistens the crop and greatly accelerates the spread of the bacterium.
Special notes for cut flowers:
To prevent spreading the bacterium from one plant to another through wounds caused by leaf and flower cutting, knives must be disinfected periodically. The more
thorough this procedure, the lower the risk of transmission via cutting tools. Although disinfecting after every cut is ideal, it is not always practical. Effective disinfections include 85% alcohol, chlorine or Menno Florades (available from Royal Brinkman). It is best to have at least five knives in rotation, allowing some to soak in disinfectant while others are in use.
Overhead irrigation
With overhead irrigation (pot culture), the risk of spreading the bacterium is considerable. The same applies in cut-flower production when overhead irrigation lines are used on growing beds. Splashing water facilitates the rapid spread of the bacterium from infected to healthy plants within the crop area. If overhead irrigation is unavoidable, adding stabilised hydrogen peroxide (H2O2) to the final part of the watering cycle is advisable to reduce bacterial spread. In practice, concentrations of up to 100 ppm are commonly used; however, frequent and prolonged peroxide use may damage the plant’s cuticle.
Restarting a crop after infection and preventing recontamination
Once the infection is under control, a new crop may be established. However, preventing recontamination is essential and can be achieved by the following measures.
- Seal off neighbouring compartments during crop clearance to protect against moisture, dust and debris.
- Remove all organic material from the infected compartment, including weeds, old leaves and organic substrates.
- Disinfection of surfaces, equipment, greenhouse structures and concrete is only effective after thorough cleaning to remove organic residues. Disinfectants work only on clean surfaces!
- In an empty greenhouse, disinfection may be carried out with formalin. Exercise extreme caution to avoid damage to adjacent crops. Irrigation lines can be treated with an acid solution for one day, followed by an alkaline solution for one day. Always ensure thorough flushing afterwards. As a guideline for acid treatment, use 1 litre nitric acid (HNO3, 38%) per 30 litres of water. For alkaline treatment, use 1 kg potassium hydroxide (KOH, 34%) per 30 litres of water. Irrigation lines must be free of root and plant remains and excessive algal growth.
- Replace existing cultivation materials wherever possible. If reuse is unavoidable, thoroughly disinfect any remaining materials. Never reuse ground cover fabric.
- If irrigation lines are reused, flush and disinfect both interior and exterior thoroughly.
- After clearing the crop, disinfect everything, including greenhouse structures and pathways.
- If possible, leave the greenhouse empty for at least six weeks before starting a new crop.
- Drip and drain lines should never be reused, as they are very difficult to disinfect.
Seek professional advice from a specialised agency for appropriate greenhouse sanitation procedures.
THIS PROBLEM CAN ONLY BE CONTROLLED THROUGH STRINGENT HYGIENE MEASURES!!
For more information, contact André Lont, Crop specialist Anthurium.
Email: al@anthura.nl
Follow the instructions for use on the label and the disinfection and cleaning rules applicable in your country. Disinfectants only work if the materials and surfaces to be disinfected have been thoroughly cleaned.
