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Poinsettia Production Four Foliar Diseases You Need to Know

Growing Poinsettias can be frustrating.

On the one hand, it’s one of the most reliable, profitable niche markets in the industry. In 2013, Poinsettia sales in the United States totalled $146 million (USDA Floriculture Crops Summary). It’s one crop consumers and businesses alike consistently buy every holiday season.

And what better way to end a year than by selling a nice crop of Poinsettias?

But at the same time, Poinsettias can be a difficult—and therefore risky—crop to grow. The inherent climate swings of their long growing season demand a lot of a grower who needs to shepherd them from propagation to finishing—without their succumbing to disease. One pest, one fungus, one bacterium left unchecked could quickly snowball and spell disaster.

Let’s leave the snowballs for wintertime and get to the business of raising healthy Poinsettias. In the spirit of know thy enemy so you can defeat them, we’ve compiled a list of four potentially devastating foliar diseases that tend to strike early in production: Erwinia, Xanthomonas, Scab, and Botrytis.

  1. Erwinia blight, caused by Erwinia carotovora. Also known as bacterial stem rot or bacterial soft rot, this is one of the most aggressive poinsettia propagation diseases. It thrives in the warm, moist conditions ideal for propagation and can develop rapidly and suddenly, leaving serious losses in its wake. One day your cuttings seem fine, and the next they are wilting, yellowing, and collapsing as the stems turn to mush. Within a few days, the cuttings turn brown and die.1 Since cuts and wounded tissue invite this disease, Erwinia usually begins at the base of the cutting.2 Note that Erwinia can sometimes be mistaken for another propagation disease, Rhizoctonia. If your diseased cuttings have a fishy odor to them and no sign of mycelium, then chances are you are dealing with Erwinia.3 Potential sources of the bacteria include surface, underground, and irrigation water; potting media; and plant debris. Insects may also play a role in its spread, creating a wound entry by feeding on the plant. High nitrogen levels are also associated with an increased susceptibility.4

    TIPS TO AVOID AND CONTROL ERWINIA BLIGHT

    Use a pasteurized, porous propagation

    Minimize leaf wetness; keep misting to a minimum.

    Minimize water splashing; avoid overhead irrigation if possible.

    Avoid high nitrogen levels.

    Follow a strict sanitation protocol: disinfect tools, knives, and benches with X3®. Employees should frequently wash hands.

    Aggressively remove any infected specimens or plant material at first indication of disease.

    Test your water. Erwinia has been isolated in surface, underground, and irrigation water sources. If you’re experiencing persistent problems with Erwinia, test to find out if it’s in your water.

    Use Phyton 27® or Phyton 35® at the preventive or therapeutic rates to help avoid or eliminate this disease. Use X3 to sanitize your equipment and destroy pathogens.

  2. Xanthomonas, caused by Xanthomonas campestris. A serious problem for the Poinsettia industry in 2010, Xanthomonas is a highly contagious and potentially serious disease for Poinsettia crops. The good news is that—as one grower’s story demonstrates—with early detection and diligence, the disease can be successfully managed. Symptoms to watch for include water-soaked, gray pinpoint spots that are typically most severe on lower leaves. As lesions develop, these spots turn yellow to tan and develop into an angular shape. The spots tend to be about 1/8” wide with irregularly raised edges and are often surrounded by a yellow halo. In severe cases, leaves may have a buckled appearance, turn yellow, and drop. New leaves will be distorted. Because this disease can be confused with scab, be sure to have any suspicious plants tested for an accurate diagnosis.5,6

    TIPS TO AVOID AND CONTROL XANTHOMONAS

    Reduce leaf wetness; keep the crop dry between waterings.

    Minimize water splash; avoid overhead irrigation if possible.

    Avoid high humidity and provide adequate spacing between plants.

    Use fans to improve air circulation.

    Follow a strict sanitation protocol: disinfect tools, knives, and benches with X3. Employees should frequently wash hands.

    Aggressively remove any infected specimens or plant material at first indication of disease.

    Use Phyton 27 or Phyton 35 at the preventive or therapeutic rates to help avoid or eliminate this disease. Use X3 to sanitize your equipment and destroy pathogens.

  3. Scab, caused by Sphaceloma poinsettiae. Though primarily a mid-season issue, this disease is very contagious during propagation when conditions are warm and wet. Recently, infected cuttings from Central America have been the source of this disease, and all cultivars are susceptible.On the stems and leaf petioles, you’ll find slightly raised circular or elongated lesions that are tan in the center and often surrounded by white, red, or purple margins. Leaf spots may not be apparent in the early stages, but once they develop are usually small, round or angular and tan in color with purple margins. Affected leaves become distorted and may yellow and drop. Because the fungus interacts with plant growth regulators to stimulate growth, in more advanced stages the stems of affected plants grow very tall while the leaves remain small. Pinching will help make it easier to detect symptoms.7,8,9

    TIPS TO AVOID AND CONTROL

    Minimize leaf wetness and water splash; avoid overhead irrigation if possible.

    Scout for plants with symptoms, particularly unusually tall plants with small leaves.

    Follow a strict sanitation protocol: disinfect tools, knives, and benches with X3. Employees should frequently wash hands.

    Aggressively remove any infected specimens or plant material at first indication of disease.

    If disease is present and you’re using overhead irrigation, start a fungicide program10  using Phyton 27 or Phyton 35 at labeled rates.

  4. Botrytis. One of the most common and serious diseases in the greenhouse, Botrytis can strike at any time during the production cycle. Poinsettia leaves, bracts, and stems are all susceptible with wounded plant tissue being the most susceptible. Look for its trademark fuzzy gray sporulation on affected plants. High humidity, moderate temperatures, and prolonged leaf wetness all favor the formation of this disease.11

    TIPS TO AVOID AND CONTROL

    Remove all diseased plant material and use a protective fungicide.

    Avoid overhead irrigation if possible.

    Improve air circulation through open mesh benching and adequate plant spacing.

    Lower Relative Humidity (RH). A few hours after sunset exchange the air by turning up the heat and opening the vents for 5 to 10 minutes. Venting the heated air will carry moisture up and away from your plants and out of your greenhouse, while the incoming cool, moist air will heat up and have a lower RH.

    Follow a strict sanitation protocol: disinfect tools, knives, and benches with X3. Employees should frequently wash hands.

    For more tips, please see our previous article, Seven Ways to Stop Botrytis.

As with all diseases, it’s important to obtain an accurate diagnosis from a laboratory as many diseases present similar symptoms. For best results, regularly rotate fungicides and bactericides to combat resistance. Phyton 27 and Phyton 35 are excellent resistance management/rotation partners and have a low risk of phytotoxicity when used as directed.


  1. Brian E. Whipker, “Poinsettia Propagation: Erwinia and Rhizoctonia,” e-Gro Alert, Vol. 3, No. 48, August 2014, http://e-gro.org/pdf/348.pdf.
  2. J. Raymond Kessler, “Poinsettia Diseases and Their Control,” Auburn University, Alabama Cooperative Extension System. http://www.aces.edu/pubs/docs/A/ANR-1272/index2.tmpl.
  3. Brian E. Whipker, “Poinsettia Propagation: Erwinia and Rhizoctonia.”
  4. J. Raymond Kessler, “Poinsettia Diseases and Their Control.”
  5. Ibid.
  6. A. R. Chase, “Poinsettia Disease Timeline,” GrowerTalks Magazine, Vol. 79, No. 2., August 2011. http://www.ballpublishing.com/growertalks/ViewArticle.aspx?articleid=18660
  7. J. Raymond Kessler, “Poinsettia Diseases and Their Control.”
  8. A. R. Chase, “Poinsettia Disease Timeline.”
  9. Ecke Ranch, “Poinsettia Scab,” http://www.ecke.com/poinsettias/productionguidelines/poinsettiascab/
  10. Bess Dicklow, UMass Plant Diagnostic Lab and Tina Smith, UMass Extension
    “Poinsettia Diseases,” University of Massachusetts Amherst, The College of Natural Sciences, Agriculture & Landscape Program, Greenhouse Crops and Floriculture Program, https://negreenhouseupdate.info/updates/poinsettia-diseases.
  11. J. Raymond Kessler, “Poinsettia Diseases and Their Control.”

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