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Four Common Poinsettia Diseases And what you can do to prevent them

Though growing Poinsettias can be challenging, it’s hard to argue they’re not worth the trouble: Poinsettias make up one of the most reliable niche markets in the industry. They are one of just a few greenhouse crops consistently sold in the final months of the year and account for the lion’s share of sales.

One of the keys to succeeding in this market is to deliver a healthy, vigorous, disease-free crop to your customers. This is easier said than done; Poinsettias are susceptible to many different diseases and problems over the course of their long growing season. This article will help you learn to identify and respond to four diseases that tend to strike early in the production cycle: Erwinia, Xanthomonas, Scab, and Botrytis. A brief description of each disease follows, along with a chart to give you at-a-glance guidance in managing these diseases.

  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
  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 with early detection and diligence, the disease can be successfully managed. (Learn how one grower conquered an early and pervasive Xanthomonas infection in this Grower Talks article.) 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
  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
  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

Since many diseases present similar symptoms, it’s always important to obtain an accurate diagnosis from a laboratory. If one or more of the above diseases strikes, Phyton 27 and Phyton 35 can be used at the curative rates—along with the appropriate cultural controls—to help your crops win the battle. See the Grower Talks article listed below for one grower’s story on how he conquered a Xanthomonas infection.

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.

RELATED:

Grower Talks Production: Xanthomonas Anxiety

Use the table below as a handy reference for identifying and managing these diseases.

PathogenSymptomsPrevention and Control
Erwinia Blight (caused by Erwinia Carotovora)
Plants wilt, yellow and collapse. Stems develop a mushy consistency. Cuttings turn brown and die. Wounded tissue susceptible, disease usually starts at the base of the cutting. Plants may have a fishy odor. Can be mistaken for Rhizoctonia; accurate diagnosis is important.
  • Use a pasteurized, porous propagation media that drains well.
  • Minimize leaf wetness. Keep misting to a minimum.
  • Avoid high nitrogen levels.
  • Follow a strict sanitation protocol. Disinfect tools, knives, and benches with a commercial-grade disinfectant such as X3®. Employees should wash hands frequently.
  • Aggressively remove any infected specimens or plant material at the first sign of disease.
  • Test your water. Erwinia has been isolated in surface, underground, and irrigation water sources.
  • Use Phyton 27® or Phyton 35® at the preventive or curative rates.
Xanthomonas (caused by Xanthomonas campestris)

Water-soaked, gray pinpoint spots, usually most severe on lower leaves. Spots turn yellow to tan and develop into an angular shape. Spots tend to be 1/8” wide with irregularly raised edges, often surrounded by a yellow halo. Can be confused with Scab; an accurate diagnosis is essential.
  • 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 a commercial-grade disinfectant such as X3®. Employees should wash hands frequently.
  • Aggressively remove any infected specimens or plant material at the first sign of disease.
  • Use Phyton 27® or Phyton 35® at the preventive or curative rates.
Scab (caused by Sphaceloma poinsettiae)
Slightly raised, circular or elongated lesions on the stems and petioles. These lesions are tan in the center and often surrounded by white, red, or purple margins. Affected leaves may become distorted, and may yellow and drop. In advanced stages, the stems will grow very tall while the leaves will remain small.
  • Minimize leaf wetness and water splash, avoid overhead irrigation if possible.
  • Scout for plants with symptoms, especially unusually tall plants with small leaves. Pinching will help in detecting this symptom.
  • Follow a strict sanitation protocol. Disinfect tools, knives, and benches with a commercial-grade disinfectant such as X3®. Employees should wash hands frequently.
  • Aggressively remove any infected specimens or plant material at the first sign of disease.
  • If disease is found and you’re using overhead irrigation, start a fungicide program10 using Phyton 27 or Phyton 35 at labeled curative rates.
Botrytis Blight (caused by Botrytis cinerea)
Fuzzy gray sporulation. Brown spots on flowers, leaves, or stems.
  • Remove all diseased plant material and use a protective fungicide, such as Phyton 27 or Phyton 35.
  • Avoid overhead irrigation if possible.
  • Improve air circulation. Use 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. This 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 article, Seven Ways to Stop Botrytis.

Download the above Disease Reference table


  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.”

* Grower Talks Production: Xanthomonas Anxiety, Roger McGaughey, head grower at Michael’s Greenhouses, © Copyright 2015 Ball Horticultural Company

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